Patent Publication Number: US-7225244-B2

Title: Common command interface

Description:
This application is a continuation-in-part of U.S. Ser. No. 09/803,783, filed Mar. 12, 2001, now abandoned entitled “VPI/VCI Availability Index”, which is a continuation-in-part of U.S. Ser. No. 09/789,665 filed Feb. 21, 2001, entitled “Out-Of-Band Network Management Channels” still pending, which is a continuation-in-part of U.S. Ser. No. 09/777,468, filed Feb. 5, 2001, entitled “Signatures for Facilitating Hot Upgrades of Modular Software Components”, still pending, which is a continuation-in-part of U.S. Ser. No. 09/756,936, filed Jan. 9, 2001, entitled “Network Device Power Distribution Scheme”, which is a continuation-in-part of U.S. Ser. No. 09/718,224, filed Nov. 21, 2000, entitled “Internal Network Device Dynamic Health Monitoring, which is a continuation-in-part of U.S. Ser. No. 09/711,054, filed Nov. 9, 2000, entitled “Network Device Identity Authentication”, which is a continuation-in-part of U.S. Ser. No. 09/703,856, filed Nov. 1, 2000, entitled “Accessing Network Device Data Through User Profiles”, which is a continuation-in-part of U.S. Ser. No. 09/687,191, filed Oct. 12, 2000 entitled “Utilizing Managed Object Proxies in Network Management Systems”, which is a continuation-in-part of U.S. Ser. No. 09/669,364, filed Sep. 26, 2000 entitled “Distributed Statistical Data Retrieval in a Network Device”, which is a continuation-in-part of U.S. Ser. No. 09/663,947, filed Sep. 18, 2000, entitled “Network Management System Including Custom Object Collections, which is a continuation-in-part of U.S. Ser. No. 09/656,123, filed Sep. 6, 2000, entitled “Network Management System Including Dynamic Bulletin Boards”, which is a continuation-in-part of U.S. Ser. No. 09/653,700, filed Aug. 31, 2000, entitled “Network Management System Including SONET Path Configuration Wizard”, which is a continuation-in-part of U.S. Ser. No. 09/637,800, filed Aug. 11, 2000, entitled “Processing Network Management Data In Accordance with Metadata Files”, which is a continuation-in-part of U.S. Ser. No. 09/633,675, filed Aug. 7, 2000, entitled “Integrating Operations Support Services with Network Management Systems”, which is a continuation-in-part of U.S. Ser. No. 09/625,101, filed Jul. 24, 2000, entitled “Model Driven Synchronization of Telecommunications Processes”, which is a continuation-in-part of U.S. Ser. No. 09/616,477, filed Jul. 14, 2000, entitled “Upper Layer Network Device Including a Physical Layer Test Port”, which is a continuation-in-part of U.S. Ser. No. 09/613,940, filed Jul. 11, 2000, entitled “Network Device Including Central and Distributed Switch Fabric Sub-Systems”, which is a continuation-in-part of U.S. Ser. No. 09/596,055, filed Jun. 16, 2000, entitled “A Multi Layer Device in One Telco Rack”, which is a continuation-in-part of U.S. Ser. No. 09/593,034, filed Jun. 13, 2000, entitled “A Network Device for Supporting Multiple Upper Layer Protocols Over a Single Network Connection”, which is a continuation and part of U.S. Ser. No. 09/574,440, filed May 20, 2000, entitled Vertical Fault Isolation in a Computer System” and U.S. Ser. No. 09/591,193, filed Jun. 9, 2000 entitled “A Network Device for Supporting Multiple Redundancy Schemes”, which is a continuation-in-part of U.S. Ser. No. 09/588,398, filed Jun. 6, 2000, entitled “Time Synchronization Within a Distributed Processing System”, which is a continuation-in-part of U.S. Ser. No. 09/574,341, filed May 20, 2000, entitled “Policy Based Provisioning of Network Device Resources” and U.S. Ser. No. 09/574,343, filed May 20, 2000, entitled “Functional Separation of Internal and External Controls in Network Devices”. 

   BACKGROUND 
   Initially, telecommunications and data communications equipment (hereinafter referred to as network devices) were administered/controlled through a Command Line Interface (CLI) that provided the user (i.e., administrator) with a textual interface through which the administrator could type in commands. CLI connections are typically made either directly with the device through a console or remotely through a telnet connection. With the growth of the Internet, web interfaces were also created to allow administrators to remotely control network devices through web pages. In general, web interfaces provide easier access with a more visually rich format through Hypertext Markup Language (HTML). For example, commands may be grouped and displayed according to particular categories and hyperlinks may be used to allow the administrator to jump between different web pages. 
   To accommodate the preferences of a large number of users and because both interfaces have advantages, often, both a CLI interface and a web interface are provided to a network device. Additional interfaces may also be provided. This flexibility, however, can be costly to maintain because although many of the commands provided on the interfaces are the same, the applications corresponding to the commands must include separate code for each interface. Thus, within, for example, an Asynchronous Transfer Mode (ATM) application, a command such as “Show ATM Stats” is essentially multiple commands: a different one for each interface. While some functions may be shared, for the most part the code for each command/interface is separate. Thus, if a command needs to be changed or upgraded, each set of code must be modified. Similarly, to add a single, new command, the application writer must develop a set of code for each interface. 
   In addition, applications running on the network device must maintain an Application Programming Interface (API) for each external interface and must be knowledgeable about the source of each received command so that responses will be provided in the appropriate format, for example, HTML for a web interface or ASCII for a CLI. If an interface is modified or the interaction between the interface and the command within the application changes, the application will likely need to be changed. For certain software architectures, this may require a new release of the software running the network device, and the network device may need to be brought down while the software is re-installed. Thus, providing different types of interfaces increases flexibility but also increases the complexity of maintaining consistent commands across each interface and the complexity of responding to commands. 
   SUMMARY 
   A common command interface (CCI) provides an interface abstraction allowing network device applications to maintain one set of code for each command regardless of which command interface (e.g., web, CLI, NMS, etc.) initiates the command. That is, the command code in each application may be shared across multiple command interfaces. The interface abstraction allows new applications including additional commands to be added to a network device and existing applications to be dynamically upgraded to include new and/or modified commands without having to modify the CCI. Thus, the network device may provide the increased flexibility of having multiple command interfaces while minimizing the complexity required to maintain commands across those interfaces. In addition, a community command interface may be used to connect the common command interfaces of multiple network devices. 
   In one aspect, the present invention provides a method of managing a telecommunications network device including registering at least one command executable by an application with a command interface, receiving the command at the command interface from a user interface, forwarding the command to the application, and completing execution of the command. 
   In another aspect, the present invention provides a method of managing a telecommunications network device including registering at least one command executable by an application with a first command proxy, wherein the first command proxy is local to the application, registering the command through the first command proxy with a central command daemon, receiving the command at a user interface, forwarding the command to a second command proxy, wherein the second command proxy is local to the user interface, forwarding the command through the second command proxy to the central command daemon, forwarding the command through the central command daemon to the first command proxy, forwarding the command through the first command proxy to the application, and completing execution of the command. 
   In yet another aspect, the present invention provides a method of managing a telecommunications network including a first network device and a second network device including executing a community command daemon on one of the first or second network devices, executing a first application on the first network device, executing a second application on the second network device, registering a first command executable by the first application with a first command interface on the first network device, registering a second command executable by the second application with a second command interface on the second network device and registering the first and second commands with the community command daemon. 
   In still another aspect, the present invention provides a telecommunications network device including an application capable of executing a command and a common command interface, wherein the application is capable of registering the command with the common command interface and the common command interface is capable of receiving the command from a user interface and forwarding the received command to the application. 
   In another aspect, the present invention provides a telecommunications network device including a common command interface and an application capable of executing a command, wherein the application includes a command application programming interface (API) for registering the command with the common command interface. 
   In yet another aspect, the present invention provides a telecommunications network including a first network device, a second network device connected to the first network device, a community command daemon executing on the first or second network device, and a first common command interface executing on the first network device and capable of registering a first command with the community command daemon, and a second common command interface executing on the second network device and capable of registering a second command with the community command daemon. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a computer system with a distributed processing system; 
       FIGS. 2   a – 2   b  are block and flow diagrams of a distributed network management system; 
       FIGS. 2   c – 2   j  are block and flow diagrams of distributed network management system clients and servers; 
       FIG. 3   a – 3   b  are block diagrams of a logical system model; 
       FIGS. 3   c  and  3   e – 3   g  are flow diagrams depicting a software build process using a logical system model; 
       FIG. 3   d  is a flow diagram illustrating a method for allowing applications to view data within a database; 
       FIG. 3   h  is a flow diagram depicting a configuration process; 
       FIGS. 3   i  and  3   l  are flow diagrams depicting template driven network services provisioning processes; 
       FIGS. 3   j – 3   k  and  3   m – 3   o  are screen displays of an OSS client and various templates; 
       FIGS. 3   n  and  3   o  are ordered list of tasks, including execute commands followed by a provisioning template type, making up a batch template type; 
       FIGS. 4   a – 4   z,    5   a – 5   z,    6   a – 6   p,    7   a – 7   y,    8   a – 8   e,    9   a – 9   n,    10   a – 10   i,    11   a – 11   m,    11   p – 11   q,    11   u  and  11   z  are screen displays of graphical user interfaces; 
       FIGS. 11   n – 11   o  are tables representing data in a configuration database; 
       FIGS. 11   r – 11   t  and  11   v – 11   w  are tables representing data in a network management system (NMS) database; 
       FIG. 11   x  is a block and flow diagram representing the creation of a user profile logical managed object including one or more groups; 
       FIG. 11   y  is a block and flow diagram of a network management system implementing user profiles and groups across multiple databases; 
       FIG. 11   z  is a representative diagram of an NMS server or a pop-up menu; 
       FIGS. 12   a  and  13   a  are block and flow diagrams of a computer system incorporating a modular system architecture and illustrating a method for accomplishing hardware inventory and setup; 
       FIGS. 12   b – 12   c  and  14   a – 14   f  are tables representing data in a configuration database; 
       FIG. 13   b  is a block and flow diagram of a computer system incorporating a modular system architecture and illustrating a method for configuring the computer system using a network management system; 
       FIGS. 13   c  and  13   d  are block and flow diagrams of an accounting subsystem for pushing network device statistics to network management system software; 
       FIG. 15  is a block and flow diagram of a line card and a method for executing multiple instances of processes; 
       FIGS. 16   a – 16   b  are flow diagrams illustrating a method for assigning logical names for inter-process communications; 
       FIG. 16   c  is a block and flow diagram of a computer system incorporating a modular system architecture and illustrating a method for using logical names for inter-process communications; 
       FIG. 16   d  is a chart representing a message format; 
       FIGS. 17–19  are block and flow diagrams of a computer system incorporating a modular system architecture and illustrating methods for making configuration changes; 
       FIG. 20   a  is a block diagram of a packaging list; 
       FIG. 20   b  is a flow diagram of a software component signature generating process; 
       FIGS. 20   c  and  20   e  are screen displays of graphical user interfaces; 
       FIG. 20   d  is a block and flow diagram of a network device incorporating a modular system architecture and illustrating a method for installing a new software release; 
       FIG. 21   a  is a block and flow diagram of a network device incorporating a modular system architecture and illustrating a method for upgrading software components; 
       FIGS. 21   b  and  21   g  are tables representing data in a configuration database; 
       FIGS. 21   c – 21   f  are screen displays of graphical user interfaces; 
       FIG. 22  is a block and flow diagram of a network device incorporating a modular system architecture and illustrating a method for upgrading a configuration database within the network device; 
       FIG. 23  is a block and flow diagram of a network device incorporating a modular system architecture and illustrating a method for upgrading software components; 
       FIG. 24  is a block diagram representing processes within separate protected memory blocks; 
       FIG. 25  is a block and flow diagram of a line card and a method for accomplishing vertical fault isolation; 
       FIG. 26  is a block and flow diagram of a computer system incorporating a hierarchical and configurable fault management system and illustrating a method for accomplishing fault escalation. 
       FIG. 27  is a block diagram of an application having multiple sub-processes; 
       FIG. 28  is a block diagram of a hierarchical fault descriptor; 
       FIG. 29  is a block and flow diagram of a computer system incorporating a distributed redundancy architecture and illustrating a method for accomplishing distributed software redundancy; 
       FIG. 30  is a table representing data in a configuration database; 
       FIGS. 31   a – 31   c,    32   a – 32   c,    33   a – 33   d  and  34   a – 34   b  are block and flow diagrams of a computer system incorporating a distributed redundancy architecture and illustrating methods for accomplishing distributed redundancy and recovery after a failure; 
       FIGS. 35   a – 35   b  are block diagrams of a network device; 
       FIGS. 36   a – 36   b  are block diagrams of a portion of a data plane of a network device; 
       FIG. 37  is a block and flow diagram of a network device incorporating a policy provisioning manager; 
       FIGS. 38 and 39  are tables representing data in a configuration database; 
       FIG. 40  is an isometric view of a network device; 
       FIGS. 41   a – 41   c  are front, back and side block diagrams, respectively, of components and modules within the network device of  FIG. 40 ; 
       FIGS. 42   a – 42   b  are block diagrams of dual mid-planes; 
       FIG. 43  is a block diagram of two distributed switch fabrics and a central switch fabric; 
       FIG. 44  is a block diagram of the interconnections between switch fabric central timing subsystems and switch fabric local timing subsystems; 
       FIGS. 45   a – 45   b  are block diagrams of a switch fabric central timing subsystem; 
       FIG. 46  is a state diagram of master/slave selection for switch fabric central timing subsystems; 
       FIGS. 47   a – 47   b  are block diagrams of a switch fabric local timing subsystem; 
       FIG. 48  is a state diagram of reference signal selection for switch fabric local timing subsystems; 
       FIG. 49  is a block diagram of the interconnections between external central timing subsystems and external local timing subsystems; 
       FIGS. 50   a – 50   c  are block diagrams of an external central timing subsystem; 
       FIG. 51  is a timing diagram of a first timing reference signal with an embedded second timing signal; 
       FIG. 52  is a block diagram of an embeddor circuit; 
       FIG. 53  is a block diagram of an extractor circuit; 
       FIGS. 54   a – 54   b  are block diagrams of an external local timing subsystem; 
       FIGS. 55   a – 55   c  are block diagrams of an external central timing subsystem; 
       FIG. 56  is a block diagram of a network device connected to test equipment through programmable physical layer test ports; 
       FIG. 57  is a block and flow diagram of a network device incorporating programmable physical layer test ports; 
       FIG. 58  is a block diagram of a test path table; 
       FIG. 59  is a block and flow diagram of a network management system incorporating proxies to improve NMS server scalability; 
       FIGS. 60   a – 60   n  are tables representing data in a configuration database; 
       FIG. 61   a  is a block diagram representing a physical managed object; 
       FIG. 61   b  is a block diagram representing a proxy; 
       FIG. 62  is a screen display of a dialog box; 
       FIGS. 63   a – 63   b  are block diagrams of a network device connected to an NMS; 
       FIG. 64  is a table representing data in an NMS database; 
       FIG. 65  is a block and flow diagram of a threshold management system; 
       FIG. 66   a – 66   e  are screen displays of a graphical user interface; 
       FIG. 67  is a screen display of a threshold dialog box; 
       FIGS. 68 ,  69   a – 69   b,    70   a – 70   b  and  71  are tables representing data in a configuration database; 
       FIG. 72   a  is a front, isometric view of a power distribution unit; 
       FIG. 72   b  is a rear, isometric view of the power distribution unit of  FIG. 72   a  without a cover; 
       FIG. 73   a  is a rear, isometric view of a network device chassis including dual midplanes; 
       FIGS. 73   b – 73   c  are enlarged views of portions of  FIG. 73   a;    
       FIG. 74  is a block and schematic diagram of a portion of a module including a power supply circuit; 
       FIGS. 75 ,  76  and  79  are screen displays of a Virtual Connection Wizard; 
       FIG. 77  is a screen display of a VPI dialog box; 
       FIG. 78  is a screen display of a VPI/VCI dialog box; 
       FIGS. 80 and 81  are block and flow diagrams of a common command interface; 
       FIG. 82  is a block and flow diagram of an application including a command API and a display API; and 
       FIG. 83  is a block and flow diagram of an extended common command interface. 
   

   DETAILED DESCRIPTION 
   Modular Software: 
   A modular software architecture solves some of the more common scenarios seen in existing architectures when software is upgraded or new features are deployed. Software modularity involves functionally dividing a software system into individual modules or processes, which are then designed and implemented independently. Inter-process communication (IPC) between the processes is carried out through message passing in accordance with well-defined application programming interfaces (APIs) generated from the same logical system model using the same code generation system. A database process is used to maintain a primary data repository within the computer system/network device, and APIs for the database process are also generated from the same logical system model and using the same code generation system ensuring that all the processes access the same data in the same way. Another database process is used to maintain a secondary data repository external to the computer system/network device; this database receives all of its data by exact database replication from the primary database. 
   A protected memory feature also helps enforce the separation of modules. Modules are compiled and linked as separate programs, and each program runs in its own protected memory space. In addition, each program is addressed with an abstract communication handle, or logical name. The logical name is location-independent; it can live on any card in the system. The logical name is resolved to a physical card/process during communication. If, for example, a backup process takes over for a failed primary process, it assumes ownership of the logical name and registers its name to allow other processes to re-resolve the logical name to the new physical card/process. Once complete, the processes continue to communicate with the same logical name, unaware of the fact that a switchover just occurred. 
   Like certain existing architectures, the modular software architecture dynamically loads applications as needed. Beyond prior architectures, however, the modular software architecture removes significant application dependent data from the kernel and minimizes the link between software and hardware. Instead, under the modular software architecture, the applications themselves gather necessary information (i.e., metadata and instance data) from a variety of sources, for example, text files, JAVA class files and database views, which may be provided at run time or through the logical system model. 
   Metadata facilitates customization of the execution behavior of software processes without modifying the operating system software image. A modular software architecture makes writing applications—especially distributed applications—more difficult, but metadata provides seamless extensibility allowing new software processes to be added and existing software processes to be upgraded or downgraded while the operating system is running (hot upgrades and downgrades). In one embodiment, the kernel includes operating system software, standard system services software and modular system services software. Even portions of the kernel may be hot upgraded under certain circumstances. Examples of metadata include, customization text files used by software device drivers; JAVA class files that are dynamically instantiated using reflection; registration and deregistration protocols that enable the addition and deletion of software services without system disruption; and database view definitions that provide many varied views of the logical system model. Each of these and other examples are described below. 
   The embodiment described below includes a network computer system with a loosely coupled distributed processing system. It should be understood, however, that the computer system could also be a central processing system or a combination of distributed and central processing and either loosely or tightly coupled. In addition, the computer system described below is a network switch for use in, for example, the Internet, wide area networks (WAN) or local area networks (LAN). It should be understood, however, that the modular software architecture can be implemented on any network device (including routers) or other types of computer systems and is not restricted to a network switch. 
   A distributed processing system is a collection of independent computers that appear to the user of the system as a single computer. Referring to  FIG. 1 , computer system  10  includes a centralized processor  12  with a control processor subsystem  14  that executes an instance of the kernel  20  including master control programs and server programs to actively control system operation by performing a major portion of the control functions (e.g., booting and system management) for the system. In addition, computer system  10  includes multiple line cards  16   a – 16   n.  Each line card includes a control processor subsystem  18   a – 18   n,  which runs an instance of the kernel  22   a – 22   n  including slave and client programs as well as line card specific software applications. Each control processor subsystem  14 ,  18   a – 18   n  operates in an autonomous fashion but the software presents computer system  10  to the user as a single computer. 
   Each control processor subsystem includes a processor integrated circuit (chip)  24 ,  26   a – 26   n,  for example, a Motorola 8260 or an Intel Pentium processor. The control processor subsystem also includes a memory subsystem  28 ,  30   a – 30   n  including a combination of non-volatile or persistent (e.g., PROM and flash memory) and volatile (e.g., SRAM and DRAM) memory components. Computer system  10  also includes an internal communication bus  32  connected to each processor  24 ,  26   a – 26   n.  In one embodiment, the communication bus is a switched Fast Ethernet providing 100 Mb of dedicated bandwidth to each processor allowing the distributed processors to exchange control information at high frequencies. A backup or redundant Ethernet switch may also be connected to each board such that if the primary Ethernet switch fails, the boards can fail-over to the backup Ethernet switch. 
   In this example, Ethernet  32  provides an out-of-band control path, meaning that control information passes over Ethernet  32  but the network data being switched by computer system  10  passes to and from external network connections  31   a – 31   xx  over a separate data path  34 . External network control data is passed from the line cards to the central processor over Ethernet  32 . This external network control data is also assigned a high priority when passed over the Ethernet to ensure that it is not dropped during periods of heavy traffic on the Ethernet. 
   In addition, another bus  33  is provided for low level system service operations, including, for example, the detection of newly installed (or removed) hardware, reset and interrupt control and real time clock (RTC) synchronization across the system. In one embodiment, this is an Inter-IC communications (I 2 C) bus. 
   Alternatively, the control and data may be passed over one common path (in-band). 
   Network/Element Management System (NMS): 
   Exponential network growth combined with continuously changing network requirements dictates a need for well thought out network management solutions that can grow and adapt quickly. The present invention provides a massively scalable, highly reliable comprehensive network management system, intended to scale up (and down) to meet varied customer needs. 
   Within a telecommunications network, element management systems (EMSs) are designed to configure and manage a particular type of network device (e.g., switch, router, hybrid switch-router), and network management systems (NMSs) are used to configure and manage multiple heterogeneous and/or homogeneous network devices. Hereinafter, the term “NMS” will be used for both element and network management systems unless otherwise noted. To configure a network device, the network administrator uses the NMS to provision services. For example, the administrator may connect a cable to a port of a network device and then use the NMS to enable the port. If the network device supports multiple protocols and services, then the administrator uses the NMS to provision these as well. To manage a network device, the NMS interprets data gathered by programs running on each network device relevant to network configuration, security, accounting, statistics, and fault logging and presents the interpretation of this data to the network administrator. The network administrator may use this data to, for example, determine when to add new hardware and/or services to the network device, to determine when new network devices should be added to the network, and to determine the cause of errors. 
   Preferably, NMS programs and programs executing on network devices perform in expected ways (i.e., synchronously) and use the same data in the same way. To avoid having to manually synchronize all integration interfaces between the various programs, a logical system model and associated code generation system are used to generate application programming interfaces (APIs)—that is integration interfaces/integration points—for programs running on the network device and programs running within the NMS. In addition, the APIs for the programs managing the data repositories (e.g., database programs) used by the network device and NMS programs are also generated from the same logical system model and associated code generation system to ensure that the programs use the data in the same way. Further, to ensure that the NMS and network device programs for managing and operating the network device use the same data, the programs, including the NMS programs, access a single data repository for configuration information, for example, a configuration database within the network device. 
   Referring to  FIG. 2   a,  in the present invention, the NMS 60 includes one or more NMS client programs  850   a – 850   n  and one or more NMS server programs  851   a – 851   n.  The NMS client programs provide interfaces for network administrators. Through the NMS clients, the administrator may configure multiple network devices (e.g., computer system  10 ,  FIG. 1 ; network device  540 ,  FIGS. 35   a – 35   b ). The NMS clients communicate with the NMS servers to provide the NMS servers with configuration requirements from the administrators. In addition, the NMS servers provide the NMS clients with network device management information, which the clients then make available to the administrators. “Pushing” data from a server to multiple clients synchronizes the clients with minimal polling. Reduced polling means less management traffic on the network and more device CPU cycles available for other management tasks. Communication between the NMS client and server is done via Remote Method Invocation (RMI) over Transmission Control Protocol (TCP), a reliable protocol that ensures no data loss. 
   The NMS client and server relationship prevents the network administrator from directly accessing the network device. Since several network administrators may be managing the network, this mitigates errors that may result if two administrators attempt to configure the same network device at the same time. 
   The present invention also includes a configuration relational database  42  within each network device and an NMS relational database  61  external to the network device. The configuration database program may be executed by a centralized processor card or a processor on another card (e.g.,  12 ,  FIG. 1 ;  542 ,  FIGS. 35   a – 35   b ) within the network device, and the NMS database program may be executed by a processor within a separate computer system (e.g.,  62 ,  FIG. 13   b ). The NMS server stores data directly in the configuration database via JAVA Database Connectivity (JDBC) over TCP, and using JDBC over TCP, the configuration database, through active queries, automatically replicates any changes to NMS database  61 . By using JDBC and a relational database, the NMS server is able to leverage database transactions, database views, database journaling and database backup technologies that help provide unprecedented system availability. Relational database technology also scales well as it has matured over many years. An active query is a mechanism that enables a client to post a blocked SQL query for asynchronous notification by the database when data changes are made after the blocked SQL query was made. 
   Similarly, any configuration changes made by the network administrator directly through console interface  852  are made to the configuration database and, through active queries, automatically replicated to the NMS database. Maintaining a primary or master repository of data within each network device ensures that the NMS and network device are always synchronized with respect to the state of the configuration. Replicating changes made to the primary database within the network device to any secondary data repositories, for example, NMS database  61 , ensures that all secondary data sources are quickly updated and remain in lockstep synchronization. 
   Instead of automatically replicating changes to the NMS database through active queries, only certain data, as configured by the network administrator, may be replicated. Similarly, instead of immediate replication, the network administrator may configure periodic replication. For example, data from the master embedded database (i.e., the configuration database) can be uploaded daily or hourly. In addition to the periodic, scheduled uploads, backup may be done anytime at the request of the network administrator. 
   Referring again to  FIG. 2   a,  for increased availability, the network device may include a backup configuration database  42 ′ maintained by a separate, backup centralized processor card (e.g.,  12 ,  FIG. 1 ;  543 ,  FIGS. 35   a – 35   b ). Any changes to configuration database  42  are replicated to backup configuration database  42 ′. If the primary centralized processor card experiences a failure or error, the backup centralized processor card may be switched over to become the primary processor and configuration database  42 ′ may be used to keep the network device operational. In addition, any changes to configuration database  42  may be written immediately to flash persistent memory  853  which may also be located on the primary centralized processor card or on another card, and similarly, any changes to backup configuration database  42 ′ may be written immediately to flash persistent memory  853 ′ which may also be located on the backup centralized processor card or another card. These flash-based configuration files protect against loss of data during power failures. In the unlikely event that all copies of the database within the network device are unusable, the data stored in the NMS database may be downloaded to the network device. Instead of having a single central processor card (e.g.,  12 ,  FIG. 1 ;  543 ,  FIGS. 35   a – 35   b ), the external control functions and the internal control functions may be separated onto different cards as described in U.S. patent application Ser. No. 09/574,343, filed May 20, 2000 and entitled “Functional Separation of Internal and External Controls in Network Devices”, which is hereby incorporated herein by reference. As shown in  FIGS. 41   a  and  41   b,  the chassis may support internal control (IC) processor cards  542   a  and  543   a  and external control (EC) processor cards  542   b  and  543   b.  In this embodiment, configuration database  42  may be maintained by a processor on internal control processor card  542   a  and configuration database  42 ′ may be maintained by a processor on internal control processor card  543   a,  and persistent memory  853  may be located on external control processor card  542   b  and persistent memory  853 ′ may be located on external control processor card  543   b.  This increases inter-card communication but also provides increased fault tolerance. 
   The file transfer protocol (FTP) may provide an efficient, reliable transport out of the network device for data intensive operations. Bulk data applications include accounting, historical statistics and logging. An FTP push (to reduce polling) may be used to send accounting, historical statistics and logging data to a data collector server  857 , which may be a UNIX server. The data collector server may then generate network device and/or network status reports  858   a – 858   n  in, for example, American Standard Code for Information Interchange (ASCII) format and store the data into a database or generate Automatic Message Accounting Format (AMA/BAF) outputs. 
   Selected data stored within NMS database  61  may also be replicated to one or more remote/central NMS databases  854   a – 854   n,  as described below. NMS servers may also access network device statistics and status information stored within the network device using SNMP (multiple versions) traps and standard Management Information Bases (MIBs and MIB-2). The NMS server augments SNMP traps by providing them over the conventional User Datagram Protocol (UDP) as well as over Transmission Control Protocol (TCP), which provides reliable traps. Each event is generated with a sequence number and logged by the data collector server in a system log database for in place context with system log data. These measures significantly improve the likelihood of responding to all events in a timely manner reducing the chance of service disruption. 
   The various NMS programs—clients, servers, NMS databases, data collector servers and remote NMS databases—are distributed programs and may be executed on the same computer or different computers. The computers may be within the same LAN or WAN or accessible through the Internet. Distribution and hierarchy are fundamental to making any software system scale to meet larger needs over time. Distribution reduces resource locality constraints and facilitates flexible deployment. Since day-to-day management is done in a distributed fashion, it makes sense that the management software should be distributed. Hierarchy provides natural boundaries of management responsibility and minimizes the number of entities that a management tool must be aware of. Both distribution and hierarchy are fundamental to any long-term management solution. The client server model allows for increased scalability as servers and clients may be added as the number of network managers increase and as the network grows. 
   The various NMS programs may be written in the JAVA programming language to enable the programs to run on both Windows/NT and UNIX platforms, such as Sun Solaris. In fact the code for both platforms may be the same allowing consistent graphical interfaces to be displayed to the network administrator. In addition to being native to JAVA, RMI is attractive as the RMI architecture includes (RMI) over Internet Inter-Orb Protocol (IIOP) which delivers Common Object Request Broker Architecture (CORBA) compliant distributed computing capabilities to JAVA. Like CORBA, RMI over IIOP uses IIOP as its communication protocol. IIOP eases legacy application and platform integration by allowing application components written in C++, SmallTalk, and other CORBA supported languages to communicate with components running on the JAVA platform. For “manage anywhere” purposes and web technology integration, the various NMS programs may also run within a web browser. In addition, the NMS programs may integrate with Hewlett Packard&#39;s (HP&#39;s) Network Node Manager (NNM™) to provide the convenience of a network map, event aggregation/filtering, and integration with other vendor&#39;s networking. From HP NNM a context-sensitive launch into an NMS server may be executed. 
   The NMS server also keeps track of important statistics including average client/server response times and response times to each network device. By looking at these statistics over time, it is possible for network administrators to determine when it is time to grow the management system by adding another server. In addition, each NMS server gathers the name, IP address and status of other NMS servers in the telecommunication network, determines the number of NMS clients and network devices to which it is connected, tracks its own operation time, the number of transactions it has handled since initialization, determines the “top talkers” (i.e., network devices associated with high numbers of transactions with the server), and the number of communications errors it has experienced. These statistics help the network administrator tune the NMS to provide better overall management service. 
   NMS database  61  may be remote or local with respect to the network device(s) that it is managing. For example, the NMS database may be maintained on a computer system outside the domain of the network device (i.e., remote) and communications between the network device and the computer system may occur over a wide area network (WAN) or the Internet. Preferably, the NMS database is maintained on a computer system within the same domain as the network device (i.e., local) and communications between the network device and the computer system may occur over a local area network (LAN). This reduces network management traffic over a WAN or the Internet. 
   Many telecommunications networks include domains in various geographical locations, and network managers often need to see data combined from these different domains to determine how the overall network is performing. To assist with the management of wide spread networks and still minimize the network management traffic sent over WANs and the Internet, each domain may include an NMS database  61  and particular/selected data from each NMS database may be replicated (or “rolled up”) to remote NMS databases  854   a – 854   n  that are in particular centralized locations. Referring to  FIG. 2   b,  for example, a telecommunications network may include at least three LAN domains  855   a – 855   c  where each domain includes multiple network devices  540  and an NMS database  61 . Domain  855   a  may be located in the Boston, Mass. area, domain  855   b  may be located in the Chicago, Ill. area and domain  855   c  may be located in the San Francisco, Calif. area. NMS servers  851   a – 851   f  may be located within each domain or in a separate domain. Similarly, one or more NMS clients may be coupled to each NMS server and located in the same domain as the NMS server or in different domains. In addition, one NMS client may be coupled with multiple NMS servers. For example, NMS servers  851   a – 851   c  and NMS clients  850   a – 850   k  may be located in domain  856   a  (e.g., Dallas, Tex.) while NMS servers  851   d – 851   f  and NMS clients  850   m – 850   u  may be located in domain  856   b  (e.g., New York, N.Y.). Each NMS server may be used to manage each domain  855   a – 855   c  or, preferably, one NMS server in each server domain  856   a – 856   b  is used to manage all of the network devices within one network device domain  855   a – 855   c.  A single domain may include network devices and NMS clients and servers. 
   Network administrators use the NMS clients to configure network devices in each of the domains through the NMS servers. The network devices replicate changes made to their internal configuration databases ( 42 ,  FIG. 2   a ) to a local NMS database  61 . In addition, the data collector server copies all logging data into NMS database  61  or a separate logging database (not shown). Each local NMS database may also replicate selected data to central NMS database(s)  854   a – 854   n  in accordance with instructions from the network administrator. Other programs may then access the central database to retrieve and combine data from multiple network devices in multiple domains and then present this data to the network administrator. Importantly, network management traffic over WANs and the Internet are minimized since all data is not copied to the central NMS database. For example, local logging data may only be stored in the local NMS databases 61 (or local logging database) and not replicated to one of the central NMS database. 
   NMS Out-Of-Band Management Channels: 
   Typically communication between an NMS client and server starts with the client connecting to the server through an application programming interface (API). For security purposes, the client generally provides a password and other user credentials, and the server provides the client with a handle. The client uses the handle in all subsequent asynchronous API calls to the server, and in each call, the client provides the server with a call back address. The server uses the call back address to respond to the client after executing the client request included in the call. Synchronous interfaces may also be provided by the server for operations that require the client to wait for a server response before proceeding. In addition, clients may register for traps with a server such that network devices connected to that server may asynchronously notify the server and, hence, clients of problems. 
   For each client connected to a server, the server allocates certain resources such as the handle assigned to each client and memory space. In addition, the server maintains a queue of client requests. Server threads are used to execute the queued client requests, and the server may allocate one thread per device or the server may maintain a pool of worker threads across all clients or for each client. 
   Since client requests are executed in the order in which they are queued, one disadvantage is that a client request to respond to a high priority situation will have to sit in the queue until all previous requests are executed. Moreover synchronous calls into the server often suspend the client until the server responds. During this period of time, the situation to be addressed by the client request may cause network errors or a complete network failure. As an example, if the control room containing the network device is on fire, the administrator would send a client request to cause the server to shut down the network device. If the request must wait in a queue, the network device may send out erroneous messages and/or cause the network to fail as it suffers damage in the fire before the server executes the client request to shut down the device. 
   Similarly, if an NMS client receives multiple notifications from one or more NMS servers, the NMS client may respond to the notifications in the order in which they were received. If a high priority notification is sent from a server to a client, for example, a notification that a network device has gone down, and the client is busy, network errors or a complete network failure may occur before the client can respond to the notification. 
   In addition, when an NMS client sends a request to an NMS server, the client typically waits for a timer to expire before acknowledging that the NMS server is experiencing difficulty and cannot respond. Moreover, once the timer expires, the NMS client has no information as to what problems the NMS server was experiencing. For example, the server may have been overloaded, the server may have crashed or the client may have lost connectivity. If an NMS server has gone down or the client has lost connectivity, during the time that the client is waiting for its timer to expire, the client will not be receiving server notifications and, thus, cannot monitor the five functional areas of network management as defined by the International Organization for Standardization (ISO), specifically, Fault, Configuration, Accounting, Performance and Security (FCAPS). As a result, the network administrator through the NMS client will not be monitoring their network. 
   Ultimately, delays in responding to high priority client requests and server notifications and disconnects between NMS clients and NMS servers affect management availability and possibly network availability. 
   To avoid these problems, one or more out-of-band management channels are provided between each NMS client and each NMS server. High priority client requests and server notifications may be sent over the out-of-band management channels to ensure fast response times. In addition, periodic roll calls between NMS clients and NMS servers may be executed over the out-of-band management channels to allow for quick discovery of any disconnects and reclaiming associated client resources. Further, periodic roll calls may be conducted between the NMS servers and the network devices to which they are connected, and if a server discovers that a network device has gone down, it may send a high priority notification to appropriate NMS clients over the out-of-band management channels to insure a fast response by the clients. 
   Referring to  FIG. 2   c,  as in typical NMS client/server connections, when an NMS client, for example, NMS client  850   a,  connects through an API  1261  with an NMS server, for example, NMS server  851   a,  the NMS client provides a password  1260  and other user credentials  1262 , and if accepted, the NMS server sends the NMS client a handle  1264  to use for all future calls to the NMS server. For additional security, the password may be encrypted. In accordance with the invention, in addition to providing a password and standard user credentials during the initial connection, the NMS client further registers a high priority API  1265  with the NMS server by providing a high priority call back address  1266 . The server may then use the high priority call back address to establish a separate connection  1268  through the high priority API (i.e., client out-of-band management channel) and send a high priority server notification to the NMS client. For example, the NMS server may send an emergency notification indicating that a network device has crashed. The connection may be established through RMI or another connection-oriented protocol such as RPC or CORBA. The client out-of-band management channel, therefore, provides an immediate communication channel between the server and client for high priority server notifications. 
   Referring to  FIG. 2   d,  each NMS client (e.g.,  850   a ) may register a high priority channel via API  1274  with each NMS server (e.g.,  851   a,    851   b,    851   e ) with which it connects. Referring to  FIG. 2   e,  instead, each NMS client (e.g.,  850   a ) may register a different high priority channel via APIs  1276   a – 1276   c  with each NMS server (e.g.,  851   a,    851   b,    851   e ) with which it connects or, referring to  FIG. 2   f,  if a limited number of high priority APIs  1278   a – 1278   b  are available to the NMS client (e.g.,  850   a ), the client may share them among the NMS servers (e.g.,  851   a,    851   b,    851   e ) with which it connects. Moreover, each client may register multiple channels via multiple APIs with each server and each channel may have a different level of priority. 
   Referring to  FIG. 2   g,  in addition to sending high priority server notifications over the client out-of-band management channels established between a server and one or more clients, the servers may periodically send roll call messages  1280   a – 1280   e  to each of the clients to which they are connected over the client out-of-band management channels to determine if the connections between each server and the clients are still valid. If a client does not respond  1282   a – 1282   e,  then a server knows the connection has been lost, and the server may take back all the resources it allocated to that client. Optionally the server may also notify one or more other clients of the lost connection. 
   Each server may also send periodic roll call messages to the network devices to which they are connected. Again, if a network device does not respond, the server knows the connection has been lost or the network device has gone down. In either case, the server sends a high priority message to the clients that are managing that device over one or more client out-of-band management channels. 
   Referring again to  FIG. 2   c,  in addition to having the client register a high priority API, the server may also register a high priority API by sending the client a high priority call back address  1270  when the server sends the client the handle. The client may then use the high priority call back address  1270  to establish a separate connection  1272  through the high priority API (i.e., server out-of-band management channel) and send high priority (e.g., emergency) client requests to the NMS server. For example, if a control room is on fire or a network device is causing network errors, the NMS client may send an emergency client request to shut down a particular network device over RMI connection  1272  using high priority call back address  1270 . 
   Different administrators may assign high priority to different situations. For example, an important customer may demand immediate resources to handle an important video conference. If given a high priority, the NMS client could then send the client request to set up the resources needed to handle the video conference through the server out-of-band management channel. 
   Referring to  FIG. 2   h,  each NMS server (e.g.,  851   a ) may register the same high priority API  1284  with each NMS client (e.g.,  850   a,    850   d,    850   g ) with which it connects. Referring to  FIG. 2   i,  instead, each NMS server (e.g.,  851   a ) may register a different high priority API  1286   a – 1286   c  with each NMS client (e.g.,  850   a,    850   d,    850   g ) with which it connects or, referring to  FIG. 2   j,  if a limited number of high priority APIs  1288   a – 1288   b  are available to the NMS server (e.g.,  851   a ), the server may share them among the NMS clients (e.g.,  850   a,    850   d,    850   g ) with which it connects. 
   In addition to sending high priority server notifications over the server out-of-band management channels established between each server and one or more clients, the clients may periodically send roll call messages to each of the servers to which they are connected over the server out-of-band management channels to determine if the connections between each client and the servers are still valid. If a server does not respond, then a client knows the connection has been lost, and the client can immediately notify the system administrator. The administrator may then cause the client to connect with another server that can also connect with the same network devices with which the previous server had been connected. During this reconnection to a new server, the NMS client may continue to run. 
   Sending high priority messages over out-of-band management channels (client and/or server) maximizes client/server management availability and, hence, network availability. Periodic roll calls between distributed points of communication—clients to servers, servers to clients and servers to devices—ensure fast discovery of lost connections, and sending notifications of lost connections over the out-of-band management channels ensures fast responses to lost connections—all of which maximizes overall management availability. 
   Logical System Model: 
   As previously mentioned, to avoid having to manually synchronize all integration interfaces between the various programs, the APIs for both NMS and network device programs are generated using a code generation system from the same logical system model. In addition, the APIs for the data repository software used by the programs are also generated from the same logical system model to ensure that the programs use the data in the same way. Each model within the logical system model contains metadata defining an object/entity, attributes for the object and the object&#39;s relationships with other objects. Upgrading/modifying an object is, therefore, much simpler than in current systems, since the relationship between objects, including both hardware and software, and attributes required for each object are clearly defined in one location. When changes are made, the logical system model clearly shows what other programs are affected and, therefore, may also need to be changed. Modeling the hardware and software provides a clean separation of function and form and enables sophisticated dynamic software modularity. 
   A code generation system uses the attributes and metadata within each model to generate the APIs for each program and ensure lockstep synchronization. The logical model and code generation system may also be used to create test code to test the network device programs and NMS programs. Use of the logical model and code generation system saves development, test and integration time and ensures that all relationships between programs are in lockstep synchronization. In addition, use of the logical model and code generation system facilitates hardware portability, seamless extensibility and unprecedented availability and modularity. 
   Referring to  FIGS. 3   a – 3   b,  a logical system model  280  is created using the object modeling notation and a model generation tool, for example, Rational Rose 2000 Modeler Edition available from Rational Software Corporation in Lexington, Mass. A managed device  282  represents the top level system connected to models representing both hardware  284  and data objects used by software applications  286 . Hardware model  284  includes models representing specific pieces of hardware, for example, chassis  288 , shelf  290 , slot  292  and printed circuit board  294 . The logical model is capable of showing containment, that is, typically, there are many shelves per chassis (1:N), many slots per shelf (1:N) and one board per slot (1:1). Shelf  290  is a parent class generalizing multiple shelf models, including various functional shelves  296   a – 296   n  as well as one or more system shelves, for example, for fans  298  and power  300 . Board  294  is also a parent class having multiple board models, including various functional boards without external physical ports  302   a – 302   n  (e.g., central processor  12 ,  FIG. 1 ;  542 – 543 ,  FIG. 35   a ; and switch fabric cards,  FIGS. 35   a  and  35   b ) and various functional boards  304   a – 304   n  (e.g., cross connection cards  562   a – 562   b  and forwarding cards  546   a – 546   e,    FIG. 35   a ) that connect to boards  306  with external physical ports (e.g., universal port cards  554   a – 554   h,    FIG. 35   a ). Hardware model  284  also includes an external physical port model  308 . Port model  308  is coupled to one or more specific port models, for example, synchronous optical network (SONET) protocol port  310 , and a physical service endpoint model  312 . 
   Hardware model  284  includes models for all hardware that may be available on computer system  10  (FIG.  1 )/network device  540  ( FIGS. 35   a – 35   b ) whether a particular computer system/network device uses all the available hardware or not. The model defines the metadata for the system whereas the presence of hardware in an actual network device is represented in instance data. All shelves and slots may not be populated. In addition, there may be multiple chassis. It should be understood that SONET port  310  is an example of one type of port that may be supported by computer system  10 . A model is created for each type of port available on computer system  10 , including, for example, Ethernet, Dense Wavelength Division Multiplexing (DWDM) or Digital Signal, Level 3 (DS3). The NMS (described below) uses the hardware model and instance data to display a graphical picture of computer system  10 /network device  540  to a user. 
   Service endpoint model  314  spans the software and hardware models within logical model  280 . It is a parent class including a physical service endpoint model  312  and a logical service endpoint model  316 . Since the links between the software model and hardware model are minimal, either may be changed (e.g., upgraded or modified) and easily integrated with the other. In addition, multiple models (e.g.,  280 ) may be created for many different types of managed devices (e.g.,  282 ). The software model may be the same or similar for each different type of managed device even if the hardware—and hardware models—corresponding to the different managed devices are very different. Similarly, the hardware model may be the same or similar for different managed devices but the software models may be different for each. The different software models may reflect different customer needs. 
   Software model  286  includes models of data objects used by each of the software processes (e.g., applications, device drivers, system services) available on computer system  10 /network device  540 . All applications and device drivers may not be used in each computer system/network device. As one example, ATM model  318  is shown. It should be understood that software model  286  may also include models for other applications, for example, Internet Protocol (IP) applications, Frame Relay and Multi-Protocol Label Switching (MPLS) applications. Models of other processes (e.g., device drivers and system services) are not shown for convenience. 
   For each process, models of configurable objects managed by those processes are also created. For example, models of ATM configurable objects are coupled to ATM model  318 , including models for a soft permanent virtual path (SPVP)  320 , a soft permanent virtual circuit (SPVC)  321 , a switch address  322 , a cross-connection  323 , a permanent virtual path (PVP) cross-connection  324 , a permanent virtual circuit (PVC) cross-connection  325 , a virtual ATM interface  326 , a virtual path link  327 , a virtual circuit link  328 , logging  329 , an ILMI reference  330 , PNNI  331 , a traffic descriptor  332 , an ATM interface  333  and logical service endpoint  316 . As described above, logical service endpoint model  316  is coupled to service endpoint model  314 . It is also coupled to ATM interface model  333 . 
   The logical model is layered on the physical computer system to add a layer of abstraction between the physical system and the software applications. Adding or removing known (i.e., not new) hardware from the computer system will not require changes to the logical model or the software applications. However, changes to the physical system, for example, adding a new type of board, will require changes to the logical model. In addition, the logical model is modified when new or upgraded processes are created. Changes to an object model within the logical model may require changes to other object models within the logical model. It is possible for the logical model to simultaneously support multiple versions of the same software processes (e.g., upgraded and older). In essence, the logical model insulates software applications from changes to the hardware models and vice-versa. 
   To further decouple software processes from the logical model—as well as the physical system—another layer of abstraction is added in the form of version-stamped views. A view is a logical slice of the logical model and defines a particular set of data within the logical model to which an associated process has access. Version stamped views allow multiple versions of the same process to be supported by the same logical model since, each version-stamped view limits the data that a corresponding process “views” or has access to, to the data relevant to the version of that process. Similarly, views allow multiple different processes to use the same logical model. 
   Code Generation System: 
   Referring to  FIG. 3   c,  logical model  280  is used as input to a code generation system  336 . The code generation system creates a view identification (id) and an application programming interface (API)  338  for each process that requires configuration data. For example, a view id and an API may be created for each ATM application  339   a – 339   n,  each SONET application  340   a – 340   n,  each MPLS application  342   a – 342   n  and each IP application  341   a – 341   n.  In addition, a view id and API is also created for each device driver process, for example, device drivers  343   a – 343   n,  and for modular system services (MSS)  345   a – 345   n  (described below), for example, a Master Control Driver (MCD), a System Resiliency Manager (SRM), and a Software Management System (SMS). The code generation system provides data consistency across processes, centralized tuning and an abstraction of embedded configuration and NMS databases (described below) ensuring that changes to their database schema (i.e., configuration tables and relationships) do not affect existing processes. 
   The code generation system also creates a data definition language (DDL) file  344  including structured query language (SQL) commands used to construct the database schema, that is, the various tables and views within a configuration database  346 , and a DDL file  348  including SQL commands used to construct various tables and SQL views within a network management (NMS) database  350  (described below). This is also referred to as converting the logical model into a database schema and various SQL views look at particular portions of that schema within the database. If the same database software is used for both the configuration and NMS databases, then one DDL file may be used for both. 
   The databases do not have to be generated from a logical model for views to work. Instead, database files can be supplied directly without having to generate them using the code generation system. Similarly, instead of using a logical model as an input to the code generation system, a MIB “model” may be used. For example, relationships between various MIBs and MIB objects may be written (i.e., coded) and then this “model” may be used as input to the code generation system. 
   Referring to  FIG. 3   d,  applications  352   a – 352   n  (e.g., SONET driver  863 , SONET application  860 , MSS  866 , etc.) each have an associated view  354   a – 354   n  of configuration database  42 . The views may be similar allowing each application to view similar data within configuration database  42 . For example, each application may be ATM version 1.0 and each view may be ATM view version 1.3. Instead, the applications and views may be different versions. For example, application  352   a  may be ATM version 1.0 and view  354   a  may be ATM view version 1.3 while application  352   b  is ATM version 1.7 and view  354   b  is ATM view version 1.5. A later version, for example, ATM version 1.7, of the same application may represent an upgrade of that application and its corresponding view allows the upgraded application access only to data relevant to the upgraded version and not data relevant to the older version. If the upgraded version of the application uses the same configuration data as an older version, then the view version may be the same for both applications. In addition, application  352   n  may represent a completely different type of application, for example, MPLS, and view  354   n  allows it to have access to data relevant to MPLS and not ATM or any other application. Consequently, through the use of database views, different versions of the same software applications and different types of software applications may be executed on computer system  10  simultaneously. 
   Views also allow the logical model and physical system to be changed, evolved and grown to support new applications and hardware without having to change existing applications. In addition, software applications may be upgraded and downgraded independent of each other and without having to re-boot computer system  10 /network device  540 . For example, after computer system  10  is shipped to a customer, changes may be made to hardware or software. For instance, a new version of an application, for example, ATM version 2.0, may be created or new hardware may be released requiring a new or upgraded device driver process. To make this a new process and/or hardware available to the user of computer system  10 , first the software image including the new process must be re-built. 
   Referring again to  FIG. 3   c,  logical model  280  may be changed ( 280 ′) to include models representing the new software and/or hardware. Code generation system  336  then uses new logical model  280 ′ to re-generate view ids and APIs  338 ′ for each application, including, for example, ATM version two  360  and device driver  362 , and DDL files  344 ′ and  348 ′. The new application(s) and/or device driver(s) processes then bind to the new view ids and APIs. A copy of the new application(s) and/or device driver process as well as the new DDL files and any new hardware are sent to the user of computer system  10 . The user can then download the new software and plug the new hardware into computer system  10 . The upgrade process is described in more detail below. Similarly, if models are upgraded/modified to reflect upgrades/modifications to software or hardware, then the new logical model is provided to the code generation system which re-generates view ids and APIs for each process/program/application. Again, the new applications are linked with the new view ids and APIs and the new applications and/or hardware are provided to the user. 
   Again referring to  FIG. 3   c,  the code generation system also creates NMS JAVA interfaces  347  and persistent layer metadata  349 . The JAVA interfaces are JAVA class files including get and put methods corresponding to attributes within the logical model, and as described below, the NMS servers use the NMS JAVA interfaces to construct models of each particular network device to which they are connected. Also described below, the NMS servers use the persistent layer metadata as well as run time configuration data to generate SQL configuration commands for use by the configuration database. 
   Prior to shipping computer system  10  to customers, a software build process is initiated to establish the software architecture and processes. The code generation system is the first part of this process. Following the execution of the code generation system, each process when pulled into the build process links the associated view id and API into its image. For example, referring to  FIG. 3   e,  to build a SONET application, source files, for example, a main application file  859   a,  a performance monitoring file  859   b  and an alarm monitoring file  859   c,  written in, for example, the C programming language (.c) are compiled into object code files (.o)  859   a ′,  859   b ′ and  859   c ′. Alternatively, the source files may be written in other programming languages, for example, JAVA (.java) or C++ (.cpp). The object files are then linked along with view ids and APIs from the code generation system corresponding to the SONET application, for example, SONET API  340   a.  The SONET API may be a library (.a) of many object files. Linking these files generates the SONET Application executable file (.exe)  860 . 
   Referring to  FIG. 3   f,  each of the executable files for use by the network device/computer system are then provided to a kit builder  861 . For example, several SONET executable files (e.g.,  860 ,  863 ), ATM executable files (e.g.,  864   a – 864   n ), MPLS executable files (e.g.,  865   a – 865   n ), MSS executable files  866   a – 866   n,  MKI executable  873   a – 873   n  files for each board and a DDL configuration database executable file  867  may be provided to kit builder  861 . The OSE operating system expects executable load modules to be in a format referred to as Executable &amp; Linkable Format (.elf). Alternatively, the DDL configuration database executable file may be executed and some data placed in the database prior to supplying the DDL file to the kit builder. The kit builder creates a computer system/network device installation kit  862  that is shipped to the customer with the computer system/network device or, later, alone after modifications and upgrades are made. To save space, the kit builder may compress each of the files included in the Installation Kit (i.e., .exe.gz, .elf.gz), and when the files are later loaded in the network device, they are de-compressed. Referring to  FIG. 3   g,  similarly, each of the executable files for the NMS is provided separately to the kit builder. For example, a DDL NMS database executable file  868 , an NMS JAVA interfaces executable file  869 , a persistent layer metadata executable file  870 , an NMS server  885  and an NMS client  886  may be provided to kit builder  861 . The kit builder creates an NMS installation kit  871  that is shipped to the customer for installation on a separate computer  62  ( FIG. 13   b ). In addition, new versions of the NMS installation kit may be sent to customers later after upgrades/modifications are made. When installing the NMS, the customer/network administrator may choose to distribute the various NMS processes as described above. Alternatively, one or more of the NMS programs, for example, the NMS JAVA interfaces and Persistent layer metadata executable files may be part of the network device installation kit and later passed from the network device to the NMS server, or part of both the network device installation kit and the NMS installation kit. 
   When the computer system is powered-up for the first time, as described below, configuration database software uses DDL file  867  to create a configuration database  42  with the necessary configuration tables and active queries. The NMS database software uses DDL file  868  to create NMS database  61  with corresponding configuration tables. Memory and storage space within network devices is typically very limited. The configuration database software is robust and takes a considerable amount of these limited resources but provides many advantages as described below. 
   As described above, logical model  280  ( FIG. 3   c ) may be provided as an input to code generation system  336  in order to generate database views and APIs for NMS programs and network device programs to synchronize the integration interfaces between those programs. Where a telecommunications network includes multiple similar network devices, the same installation kit may be used to install software on each network device to provide synchronization across the network. Typically, however, networks include multiple different network devices as well as multiple similar network devices. A logical model may be created for each different type of network device and a different installation kit may be implemented on each different type of network device. 
   Instead, of providing a logical model (e.g.,  280 ,  FIG. 3   b ) that represents a single network device, a logical model may be provided that represents multiple different managed devices—that is, multiple network devices and the relationship between the network devices. Alternatively, multiple logical models  280  and  887   a – 887   n —representing multiple network devices—may be provided, including relationships with other logical models. In either case, providing multiple logical models or one logical model representing multiple network devices and their relationships as an input(s) to the code generation system allows for synchronization of NMS programs and network device programs (e.g.,  901   a – 901   n ) across an entire network. The code generation system in combination with one or more logical models provides a powerful tool for synchronizing distributed telecommunication network applications. 
   The logical model or models may also be used for simulation of a network device and/or a network of many network devices, which may be useful for scalability testing. 
   In addition to providing view ids and APIs, the code generation system may also provide code used to push data directly into a third party code API. For example, where an API of a third party program expects particular data, the code generation system may provide this data by retrieving the data from the central repository and calling the third-party programs API. In this situation, the code generation system is performing as a “data pump”. 
   Configuration: 
   Once the network device programs have been installed on network device  540  ( FIGS. 35   a – 35   b ), and the NMS programs have been installed on one or more computers (e.g.,  62 ), the network administrator may configure the network device/provision services within the network device. Hereinafter, the term “configure” includes “provisioning services”. Referring to  FIG. 4   a,  the NMS client displays a graphical user interface (GUI)  895  to the administrator including a navigation tree/menu  898 . Selecting a branch of the navigation tree causes the NMS client to display information corresponding to that branch. For example, selecting Devices branch  898   a  within the tree causes the NMS client to display a list  898   b  of IP addresses and/or domain name server (DNS) names corresponding to network devices that may be managed by the administrator. The list corresponds to a profile associated with the administrator&#39;s user name and password. Profiles are described in detail below. 
   If the administrator&#39;s profile includes the appropriate authority, then the administrator may add new devices to list  898   b.  To add a new device, the administrator selects Devices branch  898   a  and clicks the right mouse button to cause a pop-up menu  898   c  ( FIG. 4   b ) to appear. The administrator then selects the Add Devices option to cause a dialog box  898   d  ( FIG. 4   c ) to appear. The administrator may then type in an IP address (e.g., 192.168.9.203) or a DNS name into field  898   e  and select an Add button  898   f  to add the device to Device list window  898   g  ( FIG. 4   d ). The administrator may then add one or more other devices in a similar manner. The administrator may also delete a device from the Device list window by selecting the device and then selecting a Delete button  898   h,  or the administrator may cancel out of the dialog box without adding any new devices by selecting Cancel button  898   i.  When finished, the administrator may select an OK button  898   j  to add any new devices in Device list  898   g  to navigation tree  898   a  ( FIG. 4   e ). 
   To configure a network device, the administrator begins by selecting (step  874 ,  FIG. 3   h ) a particular network device to configure, for example, the network device corresponding to IP address 192.168.9.202 ( FIG. 4   f ). The NMS client then informs (step  875 ,  FIG. 3   h ) an NMS server of the particular network device to be configured. Since many NMS clients may connect to the same NMS server, the NMS server first checks its local cache to determine if it is already managing the network device for another NMS client. If so, the NMS server sends data from the cache to the NMS client. If not, the NMS server using JDBC connects to the network device and reads the data/object structure for the physical aspects of the device from the configuration database within the network device into its local cache and uses that information with the JAVA interfaces to construct (step  876 ) a model of the network device. The server provides (step  877 ) this information to the client, which displays (step  878 ) a graphical representation  896   a  ( FIG. 4   f ) of the network device to the administrator indicating the hardware and services available in the selected network device and the current configuration and currently provisioned services. Configuration changes received by an NMS server—from either an NMS client or directly from the network device&#39;s configuration database when changes are made through the network device&#39;s CLI interface—are sent by the NMS server to any other NMS clients connected to that server and managing the same network device. This provides scalability, since the device is not burdened with multiple clients subscribing for traps, and ensures each NMS client provides an accurate view of the network device. 
   Referring to  FIGS. 4   f – 4   l , graphical representation  896   a  (i.e., device view, device mimic) in graphic window  896   b  may include many views of the network device. For example, device mimic  896   a  is shown in  FIG. 4   f  displaying a front view of the components in the upper portion of network device  540  ( FIGS. 35   a – 35   b ). The administrator may use scroll bar  926   a  to scroll down and view lower portions of the front of the network device as shown in  FIG. 4   g.  The administrator may also use image scale button  926   b  to change the size of graphic  896   a.  For example, the administrator may shrink the network device image to allow more of the device image to be visible in graphic window  896   b,  as shown in  FIG. 4   h.  This view corresponds to the block diagram of network device  540  shown in  FIG. 41   a.  For instance, upper fan tray  634  and middle fan trays  630  and  632  are shown. In addition, forwarding cards (e.g.,  546   a  and  548   e ), cross-connection cards (e.g.,  562   a,    562   b,    564   b,    566   a,    568   b ), and external processor control cards (e.g.,  542   b  and  543   b ) are shown. 
   GUI  895  also includes several splitter bars  895   a – 895   c  ( FIG. 4   f ) to allow the administrator to change the size of the various panels (e.g.,  896   b,    897  and  898 ). In addition, GUI  895  includes a status bar  895   d.  The status bar may include various fields such as a server field  895   e,  a Mode field  895   f,  a Profile field  895   g  and an active field  895   h.  The server filed may provide the IP address or DNS name of the NMS server, and the profile field may provide the username that the administrator logged in under. The active field will provide updated status, for example, ready, or ask the administrator to take particular steps. The mode field will indicate an on-line mode (i.e., typical operation) or an off-line mode (described in detail below). 
   Device mimic  896   a  may also provide one or more visual indications as to whether a card is present in each slot or whether a slot is empty. For example, in one embodiment, the forwarding cards (e.g.,  546   a  and  548   e ) in the upper portion of the network device are displayed in a dark color to indicate the cards are present while the lower slots (e.g.,  928   a  and  929   e ) are shown in a lighter color to indicate that the slots are empty. Other visual indications may also be used. For example, a graphical representation of the actual card faceplate may be added to device mimic  896   a  when a card is present and a blank faceplate may be added when the slot is empty. Moreover, this may be done for any of the cards that may or may not be present in a working network device. For example, the upper cross-connection cards may be displayed in a dark color to indicate they are present while the lower cross-connection card slots may be displayed in a lighter color to indicate the slots are empty. 
   In addition, a back view and other views of the network device may also be shown. For example, the administrator may use a mouse to move a cursor into an empty portion of graphic window  896   b  and click the right mouse button to cause a pop-up menu to appear listing the various views available for the network device. In one embodiment, the only other view is a back view and pop-up menu  927  is displayed. Alternatively, short cuts may be set up. For example, double clicking the left mouse button may automatically cause graphic  896   a  to display the back view of the network device, and another double click may cause graphic  896   a  to again display the front view. As another alternative, a pull down menu may be provided to allow an administrator to select between various views. 
   Device mimic  896   a  is shown in  FIG. 4   i  displaying a back view of the components in the upper portion of network device  540  ( FIGS. 35   a – 35   b ). Again the administrator may use scroll bar  926   a  and/or image scale button  926   b  to view lower portions ( FIGS. 4   j  and  4   k ) of the back of the network device or more of the network device by shrinking the graphic (FIG.  4   l ). These views correspond to the block diagram of network device  540  shown in  FIG. 41   b.  For example, upper fan tray  628  ( FIG. 4   i ), management interface (MI) card  621  ( FIG. 4   i ) and lower fan tray  626  ( FIG. 4   k ) are shown. In addition, universal port cards (e.g.,  556   h,    554   a  and  560   h,    FIG. 41 ), switch fabric cards (e.g.,  570   a  and  570   b ) and internal processor control cards (e.g.,  542   a  and  543   a ) are also shown. Again, graphic  896   a  may use a visual indicator to clearly show whether a card is present in a slot or whether the slot is empty. In this example, the visual indicator for universal port cards is the display of the ports available on each card. For example, universal port card  554   a  is present as indicated by the graphical representation of ports (e.g.,  930 ,  FIG. 4   l ) available on that card, while universal port card  558   a  ( FIG. 41   b ) is not present as indicated by a blank slot  931 . 
   Since the GUI has limited screen real estate and the network device may be large and loaded with many different types of components (e.g., modules, ports, fan trays, power connections), in addition to the device mimic views described above, GUI  895  may also provide a system view menu option  954  ( FIG. 4   m ). If an administrator selects this option, a separate pull away window  955  ( FIG. 4   n ) is displayed for the administrator including both a front view  955   a  and a back view  955   b  of the network device corresponding to the front and back views displayed by the device mimic. The administrator may keep this separate pull away window up and visible while provisioning services through the GUI. Moreover, the GUI remains linked with the pull away window such that if the administrator selects a component in the pull away window, the device mimic displays that portion of the device and highlights that component. Similarly, if the administrator selects a component within the device mimic, the pull away window also highlights the selected component. Thus, the pull away window may further help the administrator navigate in the device mimic. 
   Device mimic  896   a  may also indicate the status of components. For example, ports and/or cards may be green for normal operation, red if there are errors and yellow if there are warnings. In one embodiment, a port may be colored, for example, light green or gray if it is available but not yet configured and colored dark green after being configured. Other colors or graphical textures may also be used show visible status. To further ease a network administrator&#39;s tasks, the GUI may present pop-up windows or tool tips containing information about each card and/or port when the administrator moves the cursor over the card or port. For example, when the administrator moves the cursor over universal port card  556   f  ( FIG. 4   o ), pop-up window  932   a  may be displayed to tell the administrator that the card is a 16 Port OC3 Universal Port Module in Shelf 11/Slot 3. Similarly, if the administrator moves the cursor over universal port card  556   e  ( FIG. 4   p ), pop-up window  932   b  appears indicating that the card is a 16 Port OC12 Universal Port Module in Shelf 11/Slot 4, and if the cursor is moved over universal port cards  556   d  ( FIG. 4   q ) or  556   c  ( FIG. 4   r ), then pop-up windows  932   c  and  932   d  appear indicating the cards are 4 Port OC48 Universal Port Module in Shelf 11/Slot 5 and 8 Port OC12 Universal Port Module in Shelf 11/Slot 6, respectively. If the administrator moves the cursor over a port, for example, port  933  ( FIG. 4   s ), then pop-up window  932   e  appears indicating the port is an OC12 in Shelf 11/Slot 4/Port 1. 
   The views are used to provide management context. The GUI may also include a configuration/service status window  897  for displaying current configuration and service provisioning details. Again, these details are provided to the NMS client by the NMS server, which reads the data from the network device&#39;s configuration database. The status window may include many tabs/folders for displaying various data about the network device configuration. In one embodiment, the status window includes a System tab  934  ( FIG. 4   s ), which is displayed when the server first accesses the network device. This tab provides system level data such as the system name  934   a,  System Description  934   b,  System Contact  934   c,  System Location  934   d,  System IP Address  934   e  (or DNS name), System Up Time  934   f,  System identification (ID)  934   g  and System Services  934   h.  Modifications to data displayed in  934   a – 934   e  may be made by the administrator and committed by selecting the Apply button  935 . The NMS client then passes this information to the NMS server, which then writes a copy of the data in the network device&#39;s configuration database and broadcasts the changes to any other NMS clients managing the same network device. The administrator may also reset the network device by selecting the Reset System button  935   b  and then refresh the System tab data by selecting the Refresh button  935   c.    
   The status window may also include a Modules tab  936  ( FIG. 4   t ), which includes an inventory of the available modules in the network device and various details about those modules such as where they are located (e.g., shelf and slot, back or front). The inventory may also include a description of the type of module, version number, manufacturing date, part number, etc. In addition, the inventory may include run time data such as the operational status and temperature. The NMS server may continuously supply the NMS client(s) with the run time data by reading the network device configuration database or NMS database. Device mimic  896   a  is linked with status window  897 , such that selecting a module in device mimic  896   a  causes the Module tab to highlight a line in the inventory corresponding to that card. For example, if an administrator selects universal port card  556   d,  device mimic  896   a  highlights that module and the Module tab highlights a line  937  in the inventory corresponding to the card in Shelf 11/Slot 5. Similarly, if the administrator selects a line in the Module tab inventory, device mimic  896   a  highlights the corresponding module. Double clicking the left mouse button on a selected module may cause a dialog box to appear and the administrator may modify particular parameters such as an enable/disable parameter. 
   The status window may also include a Ports tab  938  ( FIG. 4   u ), which displays an inventory of the available ports in the network device and various details about each port such as where they are located (shelf, slot and port; back or front). The inventory may also include a description of the port name, type and speed as well as run time data such as administrative status, operational status and link status. Again, device mimic  896   a  is linked with status window  897  such that selecting a port within device mimic  896   a  causes the Port tab to highlight a line in the inventory corresponding to that port. For example, if the administrator selects port  939   a  (port 1, slot 4) on card  556   e,  then the Port tab highlights a line  939   b  within the inventory corresponding to that port. Similarly, if the administrator selects a line from the inventory in the Port tab, device mimic  896   a  highlights the corresponding port. Again double clicking the left mouse button on a selected port may cause a dialog box to appear and the administrator may modify particular parameters such as an enable/disable parameter. 
   Another tab in the status window may be a SONET Interface tab  940  ( FIG. 4   v ), which includes an inventory of SONET ports in the network device and various details about each port such as where they are located (shelf and slot; back or front). Medium type (e.g., SONET, Synchronous Digital Hierarchy (SDH)) may also be displayed as well as circuit ID, Line Type, Line Coding, Loopback, Laser Status, Path Count and other details. Again, device mimic  896   a  is lined with status window  897  such that selecting a port within device mimic  896   a  causes the SONET Interface tab to highlight a line in the inventory corresponding to that SONET port. For example, if the administrator selects port  941   a  (port 2, slot 5) on card  556   d,  then the SONET Interface tab highlights line  941   b  corresponding to that port. Similarly, if the administrator selects a line from the inventory in the SONET Interface tab, device mimic  896   a  highlights the corresponding port. Again, double clicking the left mouse button on a selected SONET interface may cause a dialog box to appear and the administrator may modify particular parameters such as an enable/disable parameter. 
   The System tab data as well as the Modules tab, Ports tab and SONET Interface tab data all represent physical aspects of the network device. The remaining tabs, including SONET Paths tab  942  ( FIG. 4   w ), ATM Interfaces tab  946 , Virtual ATM Interfaces tab  947  and Virtual Connections tab  948 , display configuration details and, thus, display no data until the device is configured. In addition, these configuration tabs  942 ,  946 – 948  are dialog chained together with wizard-like properties to guide an administrator through configuration details. Through these tabs within the GUI (i.e., graphical context), therefore, the administrator then makes (step  879 ,  FIG. 3   h ) configuration selections. For example, to configure a SONET path, the administrator may begin by selecting a port (e.g.,  939   a  on card  556   e,    FIG. 5   a ) within device mimic  896   a  and clicking the right mouse button (i.e., context sensitive) to cause a pop-up menu  943  to be displayed listing available port configuration options. The administrator may then select the “Configure SONET Paths” option, which causes the GUI to display a SONET Path configuration wizard  944  ( FIG. 5   b ). 
   The SONET Path configuration wizard guides the administrator through the task of setting up a SONET Path by presenting the administrator with valid configuration options and inserting default parameter values. As a result, the process of configuring SONET paths is simplified, and required administrator expertise is reduced since the administrator does not need to know or remember to provide each parameter value. In addition, the SONET Path wizard allows the administrator to configure multiple SONET Paths simultaneously, thereby eliminating the repetition of similar configuration process steps required by current network management systems and reducing the time required to configure many SONET Paths. Moreover, the wizard validates configuration requests from the administrator to minimize the potential for mis-configuration. 
   In one embodiment, the SONET Path wizard displays SONET line data  944   a  (e.g., slot 4, port 1, OC12) and three configuration choices  944   b,    944   c  and  944   d.  The first two configuration choices provide “short cuts” to typical configurations. If the administrator selects the first configuration option  944   b  ( FIG. 5   c ), the SONET Path wizard creates a single concatenated path. In the current example, the selected port is an OC12, and the single concatenated path is an STS-12c. The wizard assigns and graphically displays the position  944   e  and width  944   f  of the STS-12c path and also displays a SONET Path table  944   g  including an inventory having an entry for the SONET STS-12c path and each of the default parameters assigned to that SONET path. The position of each SONET path is chosen such that each path lines up on a valid boundary based on SONET protocol constraints. 
   If the administrator selects the second configuration option  944   c  ( FIGS. 5   d  and  5   e ), the SONET Path wizard creates one or more valid SONET paths that fully utilize the port capacity. In the current example, where the selected port is an OC12 port, in one embodiment, the second configuration option  944   c  allows the administrator to quickly create four STS-3c paths ( FIG. 5   d ) or one concatenated STS-12c ( FIG. 5   e ). The user may select the number of paths in window  944   s  or the type of path in window  944   t.  Windows  944   s  and  944   t  are linked and, thus, always present the user with consistent options. For example, if the administrator selects 4 paths in window  944   s,  window  944   t  displays STS-3c and if the administrator selects STS-12c in window  944   t,  window  944   s  displays 1 path. Again, the SONET path wizard graphically displays the position  944   d  and width  944   f  of the SONET paths created and also displays them in SONET Path table  944   g  along with the default parameters assigned to each SONET path. 
   The third configuration option allows the administrator to custom configure a port thereby providing the administrator with more flexibility. If the administrator selects the third configuration option  944   d  ( FIG. 5   f ), the SONET Path wizard displays a function window  944   h.  The function window provides a list of available SONET Path types  944   i  and also displays an allocated SONET path window  944   j.  In this example, only the STS-3c path type is listed in the available SONET Path types window, and if the administrator wishes to configure a single STS-12c path, then they need to select the first or second configuration option  944   b  or  944   c.  To configure one or more SONET STS-3c paths, the administrator selects the STS-3c SONET path type and then selects ADD button  944   k.  The SONET Path wizard adds STS-3c path  944   l  to the allocated SONET paths window and then displays the position  944   e  and width  944   f  of the SONET path and updates Path table  944   g  with a listing of that SONET path including the assigned parameters. In this example, two STS-3c paths  944   l  and  944   m  are configured in this way on the selected port. The administrator may select an allocated path (e.g.,  944   m  or  944   n ) in window  944   j  and then select the remove button  944   n  to delete a configured path, or the administrator may select the clear button  944   o  to delete each of the configured paths from window  944   j.  Moreover, the administrator may select an allocated path and use up arrow  944   u  and down arrow  944   v  to change the position  944   e.    
   In any of the SONET Path windows ( FIGS. 5   c – 5   f ), the administrator may select a path in the SONET path table and double click on the left mouse button or select a modify button  944   p  to cause the GUI to display a dialog box through which the administrator may modify the default parameters assigned to each path. The wizard validates each parameter change and prevents invalid values from being entered. The administrator may also select a cancel button  944   q  to exit the SONET path wizard without accepting any of the configured or modified paths. If, instead, the administrator wants to exit the SONET Path wizard and accept the configured SONET Paths, the administrator selects an OK button  944   r.    
   Once the administrator selects the OK button, the NMS client validates the parameters as far as possible within the client&#39;s view of the device and passes (step  880 ,  FIG. 3   h ) this run time/instance configuration data, including all configured SONET path parameters, to the NMS server. The NMS server validates (step  881 ) the data received based on its view of the world and if not correct, sends an error message to the NMS client, which notifies the administrator. Thus, the NMS server re-validates all data from the NMS clients to ensure that it is consistent with changes made by any other NMS client or by an administrator using the network device&#39;s CLI. After a successful NMS server validation, the Persistent layer software within the server uses this data to generate (step  882 ) SQL commands, which the server sends to the configuration database software executing on the network device. This is referred to as “persisting” the configuration change. Receipt of the SQL commands triggers a validation of the data within the network device as well. If the validation is not successful, then the network device sends an error message to the NMS server, and the NMS server sends an error message to the NMS client, which displays the error to the administrator. If the validation is successful, the configuration database software then executes (step  883 ) the SQL commands to fill in or change the appropriate configuration tables. 
   As just described, the configuration process provides a tiered approach to validation of configuration data. The NMS client validates configuration data received from an administrator according to its view of the network device. Since multiple clients may manage the same network device through the same NMS server, the NMS server re-validates received configuration data. Similarly, because the network device may be managed simultaneously by multiple NMS servers, the network device itself re-validates received configuration data. This tiered validation provides reliability and scalability to the NMS. 
   The configuration database software then sends (step  884 ) active query notices, described in more detail below, to appropriate applications executing within the network device to complete the administrator&#39;s configuration request (step  885 ). Active query notices may also be used to update the NMS database with the changes made to the configuration database. In addition, a Configuration Synchronization process running in the network device may also be notified through active queries when any configuration changes are made or, perhaps, only when certain configuration changes are made. As previously mentioned, the network device may be connected to multiple NMS Servers. To maintain synchronization, the Configuration Synchronization program broadcasts configuration changes to each attached NMS server. This may be accomplished by issuing reliable (i.e., over TCP) SNMP configuration change traps to each NMS server. Configuration change traps received by the NMS servers are then multicast/broadcast to all attached NMS clients. Thus, all NMS servers, NMS clients, and databases (both internal and external to the network device) remain synchronized. 
   Even a simple configuration request from a network administrator may require several changes to one or more configuration database tables. Under certain circumstances, all the changes may not be able to be completed. For example, the connection between the computer system executing the NMS and the network device may go down or the NMS or the network device may crash in the middle of configuring the network device. Current network management systems make configuration changes in a central data repository and pass these changes to network devices using SNMP “sets”. Since changes made through SNMP are committed immediately (i.e., written to the data repository), an uncompleted configuration (series of related “sets”) will leave the network device in a partially configured state (e.g., “dangling” partial configuration records) that is different from the configuration state in the central data repository being used by the NMS. This may cause errors or a network device and/or network failure. To avoid this situation, the configuration database executes groups of SQL commands representing one configuration change as a relational database transaction, such that none of the changes are committed to the configuration database until all commands are successfully executed. The configuration database then notifies the server as to the success or failure of the configuration change and the server notifies the client. If the server receives a communication failure notification, then the server re-sends the SQL commands to re-start the configuration changes. Upon the receipt of any other type of failure, the client notifies the user. 
   If the administrator now selects the same port  939   a  ( FIG. 5   a ), clicks the right mouse button and selects the Configure SONET Paths option in pop-up menu  943 , the SONET path wizard may be displayed as shown in  FIG. 5   f,  or alternatively, a SONET Path Configuration dialog box  945  ( FIG. 5   g ) may be displayed. The SONET Path dialog box is similar to the SONET Path wizard except that it does not include the three configuration options  944   b – 944   d.  Similar to the SONET Path wizard, dialog box  945  displays SONET line data  945   a  (e.g., slot 4, port 1, OC12), SONET Path table  945   g  and SONET path position  945   e  and width  945   f.  The administrator may modify parameters of a configured SONET path by selecting the path in the Path table and double clicking the right mouse button or selecting a Modify button  945   p.  The administrator may also add a SONET path by selecting an Add button  945   k,  which causes the SONET path dialog box to display another SONET path in the path table. Again, the administrator may modify the parameters by selecting the new SONET path and then the Modify button. The administrator may also delete a SONET path by selecting it within the SONET Path table and then selecting a Delete button  945   m.  The administrator may cancel any changes made by selecting a Cancel button  945   n,  or the administrator may commit any changes made by selecting an OK button  945   r.    
   The SONET path wizard provides the administrator with available and valid configuration options. The options are consistent with constraints imposed by the SONET protocol and the network device itself. The options may be further limited by other constraints, for example, customer subscription limitations. That is, ports or modules may be associated with particular customers and the SONET Path wizard may present the administrator with configuration options that match services to which the customer is entitled and no more. For example, a particular customer may have only purchased service on two STS-3c SONET paths on an OC12 SONET port, and the SONET Path wizard may prevent the administrator from configuring more than these two STS-3c SONET paths for that customer. 
   By providing default values for SONET Path parameters and providing only configuration options that meet various protocol, network device and other constraints, the process of configuring SONET paths is made simpler and more efficient, the necessary expertise required to configure SONET paths is reduced and the potential for mis-configurations is reduced. In addition, as the administrator provides input to the SONET path configuration wizard, the wizard validates the input and presents the administrator with configuration options consistent with both the original constraints and the administrator&#39;s configuration choices. This further reduces the necessary expertise required to configure SONET paths and further minimizes the potential for mis-configurations. Moreover, short cuts presented to the administrator may increase the speed and efficiency of configuring SONET paths. 
   If the administrator now selects SONET path tab  942  ( FIG. 5   h ), GUI  895  displays an inventory including the two STS-3c paths ( 942   a  and  942   b ) just configured. The SONET path tab includes information about each SONET path, such as SONET line information (e.g., shelf, slot and port), Path Position, Path Width, Ingress Connection and Egress Connection. It may also include Path Type and Service (e.g., Terminated ATM, Switched SONET), and a Path Name. The SONET Path configuration wizard may automatically assign the Path Name based on the shelf, slot and port. Parameters, such as Path Name, Path Width, Path Number and Path Type, may be changed by selecting a SONET path from the inventory and double clicking on that SONET path or selecting a Modify button (not shown) causing a dialog box to appear. The administrator may type in different parameter values or select from a pull-down list of available options within the dialog box. 
   Similarly, if the administrator selects an ATM Interfaces button  942   c  or directly selects the ATM Interfaces tab  946  ( FIG. 5   i ), GUI  895  displays an inventory including two ATM interfaces ( 946   a  and  946   b ) corresponding to the two STS-3c paths just configured. The SONET Path configuration wizard automatically assigns an ATM interface name based again on the shelf, slot and port. The SONET Path wizard also automatically assigns a minimum VPI bits and maximum VPI bits and a minimum and maximum VCI bits. Again, the ATM Interfaces tab lists information such as the shelf, port and slot as well as the Path name and location of the card. The ATM Interfaces tab also lists the Virtual ATM (V-ATM) interfaces (IF) count. Since no virtual ATM interfaces have yet been configured, this value is zero and Virtual ATM Interfaces tab  947  and Virtual Connections tab  948  do not yet list any information. The administrator may return to the SONET Paths tab to configure additional SONET paths by selecting a Back button  946   h  or by directly selecting the SONET Paths tab. 
   A Referring to  FIG. 5   j,  instead of selecting a port (e.g.,  939   a,    FIG. 5   a ) and then selecting a Configure SONET Paths option from a pop-up menu, the administrator may instead select a path from the inventory of paths in SONET Interfaces tab  940  and then select a Paths button  940   a  to cause SONET Path wizard  944  ( FIG. 5   k ) to be displayed. For example, the administrator may select line  949   a  corresponding to port  941   a  on card  556   d  and then select Paths button  940   a  to cause SONET Path wizard  944  to be displayed. As shown, SONET line data  944   a  indicates that this is port two in slot  5  and is an OC48 type port. Again, the administrator is presented with three configuration options  944   b,    944   c  and  944   d.    
   If the administrator selects option  944   b  ( FIG. 51 ), then the SONET Path Wizard creates a single STS-48c concatenated SONET Path and inventories the new path in Path table  944   g  and displays the path position  944   e  and path width  944   f.  If the administrator instead selects option  944   c  ( FIGS. 5   m – 5   o ), the SONET Path wizard creates one or more valid SONET paths that fully utilize the port capacity. For example, as pull down window  944   s  ( FIG. 5   n ) shows one single concatenated STS-48c path ( FIG. 5   n ) may be created, four STS-12c paths ( FIG. 5   m ), or sixteen STS-3c paths (FIG. S o ) may be created. 
   Instead, the administrator may select option  944   d  ( FIG. 5   p ) to custom configure the port. Again, function window  944   h  is displayed including a list of Available SONET Path types  944   i  and a list of Allocated SONET Paths  944   j.  In this instance where the port is an OC48, both an STS-3c and STS-12c are listed as available SONET Path types. The administrator may select one and then select Add button  944   k  to add a path to the Allocated SONET Paths list and cause the wizard to display the path in Path Table  944   g  and to display the path position  944   e  and width  944   f.  In this example, two STS-3c paths are added in positions  1  and  4  and two STS-12c paths are added in positions  22  and  34 . Now when the administrator selects SONET Paths tab  942  ( FIG. 5   q ), the inventory of paths includes the four new paths ( 942   c – 942   f ). Similarly, when the administrator selects ATM Interfaces tab  946  ( FIG. 5   r ), the inventory of ATM interfaces includes four new interfaces ( 946   c – 946   f ) corresponding to the newly created SONET paths. 
   Instead of selecting a port in device mimic  896   a  and then the Configure SONET Paths option from a pop-up menu and instead of selecting a SONET interface in the SONET Interfaces tab and then selecting the Paths button, the SONET Path wizard may be accessed by the administrator from any view in the GUI by simply selecting a Wizard menu button  951  and then selecting a SONET Path option  951   a  ( FIG. 5   q ) from a pull-down menu  951   b.  When the SONET path wizard appears, the SONET line data (i.e., slot, port and type) will be blank, and the administrator simply needs to provide this information to allow the SONET path wizard to select the appropriate port. If the administrator selects a port in the Ports tab prior to selecting the SONET path option from the wizard pull-down menu, then the SONET wizard will appear with this information displayed as the SONET line data but the administrator may modify this data to select a different port from the SONET wizard. 
   To create virtual connections between various ATM Interfaces/SONET Paths within the network device, the administrator first needs to create one or more virtual ATM interfaces for each ATM interface. At least two virtual ATM interfaces are required since two discrete virtual ATM interfaces are required for each virtual connection. In the case of a multipoint connection there will be one root ATM interface and many leafs. To do this, the administrator may select an ATM interface (e.g.,  946   b ) from the inventory in the ATM Interfaces tab and then select a Virtual Interfaces button  946   g  to cause Virtual Interfaces tab  947  ( FIG. 5   s ) to appear and display an inventory of all virtual interfaces associated with the selected ATM interface. In this example, no virtual ATM interfaces have yet been created, thus, none are displayed. 
   The Virtual ATM Interfaces tab also includes a device navigation tree  947   a.  The navigation tree is linked with the Virtual Interfaces button  946   g  ( FIG. 5   r ) such that the device tree highlights the ATM interface (e.g., ATM-Path2 — 11/4,  FIG. 5   s ) that was selected when the Virtual Interfaces button was selected. When the Virtual Interfaces button is selected, the NMS client automatically requests virtual interface data corresponding to the selected ATM interface from the NMS server and then the NMS client displays this data in the Virtual ATM Interfaces tab. This saves memory space within the NMS client since only a small amount of data relevant to the virtual ATM interfaces associated with the selected ATM interface must be stored. In addition, since the amount of data is small, the data transfer is quick and reduces network traffic. 
   Instead the administrator may directly select Virtual ATM Interfaces tab  947  and then use the device tree  947   a  to locate the ATM interface they wish to configure with one or more virtual ATM interfaces. In this instance, the NMS client may again automatically request virtual interface data from the NMS server, or instead, the NMS client may simply use data stored in cache. 
   To return to the ATM Interfaces tab, the administrator may select a Back button  947   d  or directly select the ATM Interfaces tab. Once the appropriate ATM interface has been selected (e.g., ATM-Path2 — 11/4/1) in the Virtual ATM Interfaces tab device tree  947   a,  then the administrator may select an ADD button  947   b  to cause a virtual ATM (V-ATM) Interfaces dialog box  950  ( FIG. 5   t ) to appear. GUI  895  automatically fills in dialog box  950  with default values for Connection type  950   a,  Version  950   b  and Administration Status  950   c.  The administrator may provide a Name or Alias  950   d  and may modify the other three parameters by selecting from the options provided in pull down menus. This and other dialog boxes may also have wizard-like properties. For example, only valid connection types, versions and administrative status choices are made available in corresponding pull-down menus. For instance, Version may be UNI Network 3.1, UNI Network 4.0, IISP User 3.0, IISP User 3.1, PNNI, IISP Network 3.0 or IISP Network 3.1, and Administration Status may be Up or Down. When Down is selected, the virtual ATM interface is created but not enabled. With regard to connection type, for the first virtual ATM interface created for a particular ATM interface, the connection type choices include Direct Link or Virtual Uni. However, for any additional virtual ATM interfaces for the same ATM interface the connection type choices include only Logical Link. Hence the dialog box provides valid options to further assist the administrator. When finished, the administrator selects an OK button  950   e  to accept the values in the dialog box and cause the virtual ATM interface (e.g.,  947   c,    FIG. 5   u ) to be inventoried in Virtual ATM tab  947 . 
   The administrator may then select ADD button  947   b  again to add another virtual ATM interface to the selected ATM interface (ATM-Path2 — 11/4/1). Instead, the administrator may use device tree  947   a  to select another ATM interface, for example, ATM path  946   c  ( FIG. 5   r ) designated ATM-Path1 — 11/5/2 ( FIG. 5   v ) in device tree  947   a.  The administrator may again select the ADD button or the administrator may select port  941   a  on card  556   d,  click the right mouse button and select the “Add Virtual Connection” option from pop-up menu  943 . This will again cause dialog box  950  ( FIG. 5   t ) to appear, and the administrator may again modify parameters and then select OK button  950   e  to configure the virtual ATM interface. 
   To create a virtual connection, the administrator selects a virtual ATM interface (e.g.,  947   c,    FIG. 5   v ) and then selects a Virtual Connections button  947   d  or a Virtual Connection option  951   c  ( FIG. 5   q ) from wizard pull-down menu  951   b.  This causes GUI  895  to start a Virtual Connection configuration wizard  952  ( FIG. 5   w ). Just as the SONET Path configuration wizard guides the administrator through the task of setting up a SONET Path, the Virtual Connection configuration wizard guides the administrator through the task of setting up a virtual connection. Again, the administrator is presented with valid configuration options and default parameter values are provided as a configuration starting point. As a result, the process of configuring virtual connections is simplified, and required administrator expertise is reduced since the administrator does not need to know or remember to provide each parameter value. In addition, the wizard validates configuration requests from the administrator to minimize the potential for mis-configuration. 
   The Virtual Connection configuration wizard includes a Connection Topology panel  952   a  and a Connection Type panel  952   b.  Within the Connection Topology panel the administrator is asked whether they want a point-to-point or point-to-multipoint connection, and within the Connection Type panel, the administrator is asked whether they want a Virtual Path Connection (VPC) or a Virtual Channel Connection (VCC). In addition, the administrator may indicate that they want the VPC or VCC made soft (SPVPC/SPVCC). Where the administrator chooses a point-to-point, VPC connection, the Virtual Connection wizard presents dialog box  953  ( FIG. 5   x ). 
   The source (e.g., test 1  in End Point 1 window  953   a ) for the point-to-point connection is automatically set to the virtual ATM interface (e.g.,  947   c,    FIG. 5   v ) selected in Virtual ATM Interface tab  947  when the virtual connection button  947   d  was selected. The administrator may change the source simply by selecting another virtual ATM interface in device tree  953   b,  for example, test 2 . Similarly, the administrator selects a destination (e.g., test 3  in End Point 2 window  953   c ) for the point-to-point connection by selecting a virtual ATM interface in device tree  953   d,  for example, test 3 . If the administrator had selected point-to-multipoint in Connection Topology panel  952   a  ( FIG. 5   w ), then the user would select multiple destination devices from device tree  953   d  or the wizard may present the administrator with multiple End Point 2 windows in which to select the multiple destination devices. In addition, if within Connection Topology panel  952   b  ( FIG. 5   w ) the administrator had elected to make the VPC or VCC soft (SPVPC/SPVCC), then the user may select in End Point 2 window  953   c  ( FIG. 5   x ) a virtual ATM interface in another network device. 
   The virtual Connection wizard also contains a Connections Parameters window  953   e,  an End Point 1 Parameters window  953   f  and an End Point 2 Parameters window  953   g.  Again for point-to-multipoint, there will be multiple End Point 2 Parameters windows. Within the Connections Parameters window, the administrator may provide a Connection name (e.g., test). The administrator also determines whether the connection will be configured in an Up or Down Administration Status, and may provide a Customer Name (e.g., Walmart) or select one from a customer list, which may be displayed by selecting Customer List button  953   h.    
   Within the End Point 1 and 2 Parameters windows, the administrator provides a Virtual Path Identifier (VPI) in window  953   i,    953   j  or selects a Use Any VPI Value indicator  953   k,    953   l.  If the administrator chooses a VCC connection in Connection Type window  952   b  ( FIG. 5   w ), then the administrator must also provide a Virtual Channel Indicator (VCI) in window  953   m,    953   n  or select a Use Any VCI Value indicator  953   o,    953   p.  The administrator also selects a Transmit and a Receive Traffic Descriptor (e.g., Variable Bit Rate (VBR)-high, VBR-low, Constant Bit Rate (CBR)-high, CBR-low) from a pull down menu or selects an Add Traffic Descriptor button  953   q,    953   r.  If the administrator selects one of the Add Traffic Descriptor buttons, then a traffic descriptor window  956  ( FIG. 5   y ) is displayed and the administrator may add a new traffic descriptor by providing a name and selecting a quality of service (QoS) class and a traffic descriptor type from corresponding pull down menus. Depending upon the QoS class and type selected, the administrator may also be prompted to input peak cell rate (PCR), sustainable cell rate (SCR), maximum burst size (MBS) and minimum cell rate (MCR), and for each PCR, SCR, MBS and MCR, the administrator will be prompted for a cell loss priority (CLP) value where CLP=0 corresponds to high priority traffic and CLP=0+1 corresponds to combined/aggregated high and low priority traffic. The traffic descriptors indicate the priority of the traffic to be sent over the connection thereby allowing parameterization of quality of service. The administrator may select a Use the same Traffic Descriptor for both Transmit and Receive indicator  953   s,    953   t  ( FIG. 5   x ). 
   Within the Virtual Connection wizard, the administrator may select a Back button  953   u  ( FIG. 5   x ) to return to screen  952  ( FIG. 5   w ) or a Cancel button  953   v  to exit out of the wizard without creating a virtual connection. On the other hand, if the administrator has provided all parameters and wants to commit the virtual connection, then the administrator selects a Finish button  953   w.  The NMS client passes the parameters to the NMS server, which validates the data and then writes the data into the network device&#39;s configuration database. The data is validated again within the network device and then through active queries modular processes throughout the device are notified of the configuration change to cause these processes to implement the virtual connection. GUI  895  then displays the newly created virtual connection  948   a  ( FIG. 5   z ) in a list within Virtual Connections tab  948 . The administrator may then create multiple virtual connections between the various virtual ATM interfaces, each of which will be listed in the Virtual Connections tab  948 . The administrator may also select a Back button  948   b  to return to the Virtual ATM Interfaces tab or select the Virtual ATM Interfaces tab directly. 
   The Virtual Connections tab also includes a device navigation tree  948   c.  The device tree is linked with Virtual Connections button  947   d  such that the device tree highlights the virtual ATM interface that was selected in Virtual ATM Interfaces tab  947  when the Virtual Connections button was selected. The Virtual Connections tab then only displays data relevant to the highlighted portion of the device tree. 
   As described above, the SONET Paths tab, ATM Interfaces tab, Virtual ATM Interfaces tab and Virtual Connections tabs are configuration tabs that are chained together providing wizard-like properties. Both the order of the tabs from right to left and the forward buttons (e.g., ATM Interfaces button  942   c ) and back buttons (e.g., Back button  946   h ) allow an administrator to easily and quickly sequence through the steps necessary to provision services. Although device navigation trees were shown in only the Virtual ATM Interface tab and the Virtual Connection tab, a device navigation tree may be included in each tab and only data relevant to the highlighted portion of the navigation tree may be displayed. 
   In addition to the SONET Interface and SONET Paths tabs, the status window may include tabs for other physical layer protocols, for example, Ethernet. Moreover, in addition to the ATM Interfaces and Virtual ATM Interfaces tabs, the status window may include tabs for other upper layer protocols, including MPLS, IP and Frame Relay. Importantly, other configuration wizards in addition to the SONET Path configuration wizard and Virtual Connection configuration wizard may also be used to simplify service provisioning. 
   VPI/VCI Availability Index: 
   When configuring a Permanent Virtual Circuit (PVC) or a Soft Permanent Virtual Circuit (SPVC) on a virtual Asynchronous Transfer Mode (ATM) interface, a network administrator must specify at least a Virtual Path Identifier (VPI) and, in many instances, both a VPI and a Virtual Channel Identifier (VCI). If the network device being configured is not the first end-point of the connection being established, then the network administrator will simply provide the VPI or VPI/VCI value supplied by the connection request. If, however, the network device being configured is the first end-point in the connection being established, the network administrator must provide an unused (i.e., available) VPI or VPI/VCI value. 
   Providing an available VPI or VPI/VCI can be very difficult due to the large number of possible VPIs and VCIs on a network. In an ATM cell header, a VPI is identified using 8 bits for a User Network Interface (UNI) and 12 bits for a Network Node Interface (NNI). Thus, for a UNI ATM connection there are 256 possible VPIs and for an NNI ATM connection there are 4000 possible VPIs. Each VCI is identified by 16 bits, for a total of 64,000 possible VCIs for each possible VPI. 
   Typically, allocated VPIs and VCIs are tracked manually. Thus, tracking each allocated VPI and VCI is cumbersome and error prone. Without accurate checking, however, the network administrator&#39;s task of assigning an unused VPI or VPI/VCI to a first end-point in a connection becomes a frustrating and time consuming guessing game. The administrator inputs what they believe is an available value and waits to see if it is accepted or rejected. If it is rejected, they repeat the process of inputting another value they believe is available and again waiting to see if it is accepted or rejected. In a network where thousands and, perhaps, millions of virtual connections (PVCs) need to be configured, this guessing game is an unacceptable waste of time. In addition, if an invalid value is not rejected, misconfiguration errors may occur on the network. 
   Newer network/element management systems (“NMSs”) offer automatic selection of VPI and VPI/VCI values. This eliminates the tracking burden and guess work frustration but the administrator loses control over which values are selected. In addition, the administrator is often unaware of which value is selected. 
   In Virtual Connection Wizard  953  ( FIG. 5   x ), a network administrator may input an available VPI value in windows  953   i  and  953   j  or allow the wizard to automatically input an available VPI value by selecting Use Any VPI Value indicators  953   k  and  953 L. Similarly, a network administrator may input an available VCI value in windows  953   m  and  953   n  or allow the wizard to automatically input an available VCI value by selecting Use Any VCI Value indicators  953   o  and  953   p.  The automatic inputting of available VPIs and VCIs removes any requirement that network administrators track allocated VPIs and VCIs and eliminates the frustrating guessing game that often occurs when the tracking is inaccurate. Automatic selection, however, removes the network administrator&#39;s control over which available VPI or VCI is chosen. 
   To provide the network administrator with more control while also eliminating the need to track allocated VPIs and VCIs, a Virtual Connection Wizard may provide VPI Index buttons and VPI/VCI Index buttons. When selected the Index buttons provide the administrator with a list of available VPIs and VCIs from which the administrator may choose. For example, a Virtual Connection Wizard  1102  provides VPI Index buttons  1102   a  and  1102   b  ( FIG. 75 ) if the network administrator selects the Virtual Path Connection option in Connection Type panel  952   b  ( FIG. 5   w ) and provides VPI/VCI Index buttons  1102   c  and  1102   d  ( FIG. 76 ) if the network administrator selects the Virtual Channel Connection option in Connection Type panel  952   b.    
   Selecting VPI Index buttons  1102   a  or  1102   b  causes a VPI Index dialog box  1104  ( FIG. 77 ) to appear. Dialog box  1104  includes a VPI window  1104   a  and backward and forward scroll buttons  1104   b  and  1104   c,  respectively. When dialog box  1104  first appears, the VPI window lists the first available VPI (e.g., 10). The administrator may then use forward scroll button  1104   c  to cause succeeding available VPI values (e.g., 14, 16, 25, etc.) to appear in dialog VPI window  1104   a.  Similarly, the administrator may use backward scroll button  1104   b  to cause previous available VPI values (e.g., 16, 14, 10) to appear in dialog VPI window  1104   a.  Once the administrator determines which VPI they wish to allocate to the new connection, the administrator may click on cancel button  1104   d  and type the value into wizard VPI windows  1102   e  and  1102   f  ( FIG. 75 ) or, if the administrator has the desired value showing in dialog VPI window  1104   a,  the administrator need only select OK button  1104   e  and the Virtual Connection Wizard will automatically add that value to wizard VPI windows  1102   e  and  1102   f.    
   Similarly, selecting VPI/VCI Index buttons  1102   c  or  1102   d  ( FIG. 76 ) causes a VPI/VCI Index dialog box  1106  ( FIG. 78 ) to appear. Dialog box  1106  includes a VPI window  1106   a  and a VCI window  1106   b  and backward and forward scroll buttons  1106   c – 1106   f.  When dialog box  1106  first appears, the VPI window lists the first available VPI (e.g., 10) and the VCI window lists the first available VCI (e.g., 4). The administrator may then use forward scroll button  1106   d  to cause succeeding available VPI values (e.g., 14, 16, 25, etc.) to appear in dialog VPI window  1106   a  and forward scroll button  106   f  to cause succeeding available VCI values (e.g., 8, 9, 15, 22, etc.) to appear in dialog VCI window  1106   b.  Similarly, the administrator may use backward scroll button  1106   c  to cause previous available VPI values (e.g., 16, 14, 10) to appear in dialog VPI window  1106   a  and backward scroll button  1106   e  to cause previous available VCI values (e.g., 15, 9, 8, 4) to appear in dialog VCI window  1106   b.  Once the administrator determines which VPI/VCI they wish to allocate to the new connection, the administrator may click on cancel button  1106   g  and type the desired VPI number into wizard VPI windows  1102   e  and  1102   f  ( FIG. 76 ) and type the desired VCI number into wizard VCI windows  1102   g  and  1102   h  or, if the administrator has the desired VPI/VCI values showing in dialog VPI and VCI windows  1106   a  and  1106   b,  the administrator need only select OK button  1106   h  and the Virtual Connection Wizard will automatically add those values to wizard VPI and VCI windows  1102   e – 1102   h.    
   Referring to  FIG. 79 , instead of providing VPI and VPI/VCI Index buttons and using VPI and VPI/VCI dialog boxes, the wizard VPI windows  1102   e  and  1102   f  and the VCI windows  1102   g  and  1102   h  may be “spin boxes” including up and down arrows  1102   i  and  1102   j,  respectively. Using the up and down arrows, preceding and succeeding values may be scrolled through the corresponding window, and the administrator would simply stop scrolling when the desired values were displayed. The indexes of available VPIs and VCIs may be displayed to an administrator in a variety of ways, each such way will be referred to hereinafter as an Availability Index. 
   Availability Indexes present administrators with valid, available values. Thus, the guesswork and tracking burden are removed from the VPI/VCI selection process and less time and frustration is required to configure connections. Yet, the administrator retains control over exactly which paths and channels are allocated for each connection. Consequently, an administrator may choose to keep all connections for a particular customer on a particular path or set of paths. Similarly, the administrator may designate a certain set of paths for virtual path connections and a different set of paths for virtual channel connections. Since only valid, available values are presented to the administrator, less experienced administrators may easily configure connections without fear of misconfiguration errors. 
   Custom Navigator: 
   In typical network management systems, the graphical user interface (GUI) provides static choices and is not flexible. That is, the screen flow provided by the GUI is predetermined and the administrator must walk through a predetermined set of screens each time a service is to be provisioned. To provide flexibility and further simplify the steps required to provision services within a network device, GUI  895 , described in detail above, may also include a custom navigator tool that facilitates “dynamic menus”. When the administrator selects the custom navigator menu button  958  ( FIG. 4   x ), a pop-up menu  958   a  displays a list of available “screen marks”. The list of screen marks may include default screen marks (e.g., Virtual ATM IF  958   b  and Virtual Connection  958   c ) and/or administrator created screen marks (e.g., test  958   d ). 
   When the administrator selects a particular screen mark, the custom navigator shortcuts the configuration process by jumping forward past various configuration screens to a particular configuration screen corresponding to the screen mark. For example, if the administrator selects a Virtual ATM IF screen mark  958   b,  the custom navigator presents the Virtual ATM Interface tab ( FIG. 5   u ). The administrator may then select an ATM interface from device tree  947   a  and select Add button  947   b  to add a virtual ATM interface. Similarly, the administrator may select a Virtual Connection screen mark  958   c,  and the custom navigator automatically presents Virtual Connection wizard  952  ( FIG. 5   w ). 
   Moreover, the custom navigator allows the administrator to create unique screen marks. For example, the administrator may provision SONET paths and ATM interfaces as described above, then select an ATM interface (e.g.,  946   b,    FIG. 5   r ) in ATM interfaces tab  946  and select Virtual Interfaces button  946   g  to display Virtual ATM Interfaces tab  947  ( FIG. 5   s ), and as described above, the devices tree  947   a  will highlight the selected ATM interface. If the administrator believes they may want to return to the Virtual Interfaces tab multiple times to provision multiple virtual ATM interfaces for the selected ATM interface or other ATM interfaces near the selected ATM interface in device tree  947   a,  then the administrator would select a screen mark button  959  to create a screen mark for this configuration position. A dialog box would appear in which the administrator enters the name of the new screen mark (e.g., test  958   d,    FIG. 4   x ) and this new screen mark name is added to the list of screen marks  958   a.  The custom navigator then takes a “snap shot” of the metadata necessary to recreate the screen and the current configuration position (i.e., highlight ATM-Path2 — 11/4/1). If the administrator now selects this screen mark while another tab is displayed, the custom navigator uses the metadata associated with the screen mark to present the screen shot displayed in  FIG. 5   s  to the administrator updated with any other configuration changes made subsequent to the creation of the screen mark. 
   As a result, the administrator is provided with configuration short cuts, both default short cuts and ones created by the administrator himself. Many other screen marks may be created through GUI  895 , and in each case, the screen marks may simplify the configuration process and save the administrator configuration time. 
   Custom Wizard: 
   To provide additional flexibility and efficiency, an administrator may use a custom wizard tool to create unique custom wizards to reflect common screen sequences used by the administrator. To create a custom wizard, the administrator begins by selecting a Custom Wizard menu button  960  ( FIG. 4   y ) to cause a pull-down menu  960   a  to appear and then selecting a Create Wizard  960   b  option from the pull-down menu. The administrator then begins using the particular sequence of screens that they wish to turn into a custom wizard and the custom wizard tool records this sequence of screens. For example, the administrator may begin by selecting a port within device mimic  896   a,  clicking the right mouse button and selecting the Configure SONET Paths option to cause the SONET Path configuration wizard  944  ( FIG. 5   b ) to appear. The custom wizard tool records the first screen to be included in the new custom wizard as the SONET Path configuration wizard screen  944 . After filling in the appropriate data for the current port configuration, the administrator presses the OK button and the SONET Paths tab  942  ( FIG. 5   h ) appears. The custom wizard records the SONET Paths tab screen as the next screen in the new custom wizard. The administrator may then select Virtual ATM interfaces tab  947  ( FIG. 5   s ) to cause this tab to be displayed. Again, the custom navigator records this screen as the next screen in the new custom wizard. 
   The administrator may continue to select further screens to add to the new custom wizard (for example, by selecting an ATM interface from device tree  947   a  and then selecting the Add button  947   b  to cause the Add V-ATM Interface dialog box  950  ( FIG. 5   t ) to appear) or, if the administrator is finished sequencing through all of the screens that the administrator wants added to the new custom wizard, the administrator again selects Custom Wizard menu button  960  ( FIG. 4   y ) and then selects a Finish Wizard option  960   c.  This causes a dialog box  960   d  to appear, and the administrator enters a name (e.g., test) for the custom wizard just created. 
   To access a custom wizard, the administrator again selects Custom Wizard  960  menu button and then selects a Select Wizard option  960   e  to cause an inventory  960   f  of custom wizards to be displayed. The administrator then selects a custom wizard (e.g., test), and the custom wizard automatically presents the administrator with the first screen of that wizard. In the continuing example, the custom navigator presents SONET Path configuration wizard screen  961  ( FIG. 4   z ). Since the administrator may start a custom wizard from any screen within GUI  895 , SONET Path wizard screen  961  is different from the screen  944  displayed in  FIG. 5   b  because SONET line data  961   a  (i.e., slot, port, type) is not provided. That is, the administrator may not have selected a particular SONET Path to configure prior to selecting the custom wizard. Hence, the SONET line data is blank and the administrator must fill this in. After the administrator enters and/or modifies the SONET line data and any other data within the first screen, the administrator selects a Next button  961   b  (or an OK button) to move to the next screen in the sequence of screens defined by the custom wizard. In the next and subsequent screens, the administrator may also select a Back button to return to a previous screen within the custom wizard screen sequence. Thus, the custom wizard tool allows an administrator to make their provisioning tasks more efficient by defining preferred screen sequences for each task. 
   Off-Line Configuration: 
   There may be times when a network manager/administrator wishes to jump-start initial configuration of a new network device before the network device is connected into the network. For example, a new network device may have been purchased and be in the process of being delivered to a particular site. Generally, a network manager will already know how they plan to use the network device to meet customer needs and, therefore, how they would like to configure the network device. Because configuring an entire network device may take considerable time once the device arrives and because the network manager may need to get the network device configured as soon as possible to meet network customer needs, many network managers would like the ability to perform preparatory configuration work prior to the network device being connected into the network. 
   In the current invention, network device configuration data is stored in a configuration database within the network device and all changes to the configuration database are copied in the same format to an external NMS database. Since the data in both databases (i.e., configuration and NMS) is in the same format, the present invention allows a network device to be completely configured “off-line” by entering all configuration data into an NMS database using GUI  895  in an off-line mode. When the network device is connected to the network, the data from the NMS database is reliably downloaded to the network device as a group of SQL commands using a relational database transaction. The network device then executes the SQL commands to enter the data into the internal configuration database, and through the active query process (described below), the network device may be completely and reliably configured. 
   Referring to  FIG. 6   a,  the network manager begins by selecting Devices branch  898   a  in navigation tree  898 , clicking the right mouse button to cause pop-up menu  898   c  to appear and selecting the Add Devices option causing dialog box  898   d  ( FIG. 6   b ) to be displayed. The network manager then enters the intended IP address or DNS name (e.g., 192.168.9.201) of the new network device into field  898   e  and de-selects a Manage device in on-line mode option  898   k —that is, the network manager moves the cursor over box  898   l  and clicks the left mouse button to clears box  898   l.  De-selecting the Manage device in on-line mode option indicates that the network device will be configured in off-line mode. The network manager then selects Add button  898   f  to cause dialog box  898   d  to add the IP address to window  898   g  ( FIG. 6   c ). However, in this example, box  898   m  is blank indicating the network device is to be configured off-line. 
   Referring to  FIG. 6   d,  the new network device (e.g., 192.168.9.201) is now added to the list of devices  898   b  to be managed. However, the icon includes a visual indicator  898   n  (e.g., red “X”) indicating the off-line status of the device. To begin off-line configuration, the network manager selects the new device. Since the NMS client and NMS server are not connected to the actual network device, no configuration data may be read from the network device&#39;s configuration database. The network manager must, therefore, populate a device mimic with modules representing the physical inventory that the network device will include. To do this, the network manager begins by clicking on the right mouse button to display pop-up menu  898   o,  and selects the Add Chassis option to cause a device mimic  896   a  ( FIG. 6   e ) to be displayed in window  896   b  including only a chassis. All slots in the chassis may be empty and visually displayed, for example, in a gray or light color. Alternatively, particular modules that are required for proper network device operation may be automatically included in the chassis. If more than one chassis type is available, a dialog box would appear and allow the network manager to select a particular chassis. In the current example, only one chassis is available and is automatically displayed when the network manager selects the Add Chassis option. 
   Again, the cursor provides context sensitive pop-up windows. For example, the network manager may move the cursor over a particular slot (e.g.,  896   c,    FIG. 6   e ) to cause a pop-up window (e.g.,  896   d ) to appear and describe the slot (e.g., Empty Forwarding Processor Slot Shelf 3/Slot 1). The network manager may then select an empty slot (e.g.,  896   c,    FIG. 6   f ) to cause the device mimic to highlight that slot, click the right mouse button to cause a pop-up menu (e.g.,  896   e ) to appear and select the Add Module option. In this example, only one type of forwarding card is available. Thus, it is automatically added (visually indicated in dark green,  FIG. 6   g ) to the device mimic. This forwarding card corresponds to forwarding card  546   a  in  FIG. 41   a.  The network manager may also remove a module by selecting the module (e.g.,  546   a ), clicking the right mouse button to cause a pop-up menu  896   t  to appear and then selecting the Remove Module option. 
   If there are multiple types of modules that may be inserted in a particular slot, then a dialog box will appear after the network manager selects the Add Module option and the network manager will select the particular module that the network device will include in this slot upon delivery. For example, while viewing the back of the chassis ( FIG. 6   h ), the manager may select an empty universal port card slot (e.g.,  896   f ), click the right mouse button causing pop-up menu  896   g  ( FIG. 6   i ) to appear and select the Add Module option. Since multiple universal port cards are available, selecting the Add Module option causes a dialog box  896   h  ( FIG. 6   j ) to appear. The network manager may then select the type of universal port card to be added into the empty slot from an inventory provided in pull-down menu  896   i  ( FIG. 6   k ). Once the network manager selects the appropriate card and an OK button  896   j,  the device mimic adds a representation of this card (e.g.,  556   h,    FIG. 61  and see also  FIG. 41   b ). 
   Typically, a network device may include many similar modules, for example, many 16 port OC3 universal port cards and many forwarding cards. Instead of having the network manager repeat each of the steps described above to add a universal port card or a forwarding card, the network manager may simply select an inserted module (e.g., 16 port OC3 universal port card  556   h,    FIG. 6L ) by pressing down on the left mouse button, dragging an icon to an empty slot (e.g.,  556   i ) also requiring a similar module and releasing the left mouse button to drop a similar module (e.g., 16 port OC3 universal port card  556   g,    FIG. 6   m ) into that empty slot. Similarly, the network manager may drag and drop a forwarding card module to an empty forwarding card slot and other inserted modules into other empty slots. The network manager may use the drag and drop method to quickly populate the entire network device with the appropriate number of similar modules. To add a different type of universal port card, the network manager will again select the empty slot, click on the right mouse button, select the Add Module button from the pop-up menu and then select the appropriate type of universal port card from the dialog box. 
   Once the network manager is finished adding appropriate modules into the empty slots such that the device mimic represents the physical hardware that will be present in the new network device, then the network manager may configure/provision services within the network device. Off-line configuration is the same as on-line configuration, however, instead of sending the configuration data to the configuration database within the network device, the NMS server stores the configuration data in an external NMS database. After the network device arrives and the network manager connects the network device&#39;s ports into the network, the network manager selects the device (e.g., 192.168.9.201,  FIG. 6   n ), clicks the right mouse button to cause pop-up menu  868   o  to appear and selects the Manage On-line option. 
   The NMS client notifies the NMS server that the device is now to be managed on-line. The NMS server first reconciles the physical configuration created by the network manager and stored in the NMS database against the physical configuration of the actual network device and stored in the internal configuration database. If there are any mis-matches, the NMS server notifies the NMS client, which then displays any discrepancies to the network manager. After the network manager fixes any discrepancies, the network manager may again select the Manage On-Line option in pop-up menu  898   o.  If there are no mis-matches between the physical device tables in the NMS database and the configuration database, then the NMS server reconciles all service provisioning data in the NMS database against the service provisioning data in the configuration database. In this example, the network device is new and thus, the configuration database has no service provisioning data. Thus, the reconciliation will be successful. 
   The NMS server then instructs the network device to stop replication between the primary configuration database within the network device and the backup configuration database within the network device. The NMS server then pushes the NMS database data into the backup configuration database, and then instructs the network device to switchover from the primary configuration database to the backup configuration database. If any errors occur after the switchover, the network device may automatically switch back to the original primary configuration database. If there are no errors, then the network device is quickly and completely configured to work properly within the network while maximizing network device availability. 
   In the previous example, the network manager configured one new network device off-line. However, a network manager may configure many new network devices off-line. For example, a network manager may be expecting the receipt of five or more new network devices. Referring to  FIG. 6   o,  to simplify the above process, a network manager may select an on-line device (e.g., 192.168.9.202) or off-line device (e.g., 192.168.9.201) by pressing and holding the left mouse button down, dragging an icon over to a newly added off-line device (e.g., 192.168.203) and dropping the icon over the newly added off-line device by releasing the left mouse button. The NMS client notifies the NMS server to copy the configuration data from the NMS database associated with the first network device (e.g., 192.168.9.202 or 192.168.9.201) to a new NMS database associated with the new network device and to change the data in the new NMS database to correspond to the new network device. The network manager may then select the new network device and modify any of the configuration data, as described above, to reflect the current network device requirements. As a result, off-line mode configuration is also made more efficient. 
   A network manager may also choose to re-configure an operational device in off-line mode without affecting the operation of the network device. For example, the network manager may want to add one or more new modules or provision services in a network device during a time when the network sees the least amount of activity, for example, midnight. Through the off-line mode, the network manager may prepare the configuration data ahead of time. 
   Referring to  FIG. 6   p,  the network manager may select an operational network device (e.g., 192.168.9.202), click on the right mouse button to cause pop-up menu  898   o  to appear and select the Manage On-Line option, which de-selects the current on-line mode and causes the GUI to enter an off-line mode for this device. Although the GUI has entered the off-line mode, the network device is still operating normally. The network manager may then add one or more modules and/or provision services as described above just as if the GUI were still in on-line mode, however, all configuration changes are stored by the NMS server in the NMS database corresponding to the network device instead of the network device&#39;s configuration database. Alternatively, when the NMS server is notified that a network device is to be managed off-line, the NMS server may copy the NMS database data to a temporary NMS database and store all off-line configuration changes there. When the network manager is ready (i.e., at the appropriate time and/or after adding any new modules to the network device) to download the configuration changes to the operational network device, the network manager again selects the network device (e.g., 192.168.9.202), clicks on the right mouse button to cause pop-up menu  898   a  to appear and selects the Manage On-Line option. 
   The NMS client notifies the NMS server that the device is now to be managed on-line. The NMS server first reconciles the physical configuration stored in the NMS database (or the temporary NMS database) against the physical configuration of the actual network device stored in the internal configuration database. If there are any mis-matches, the NMS server notifies the NMS client, which then displays any discrepancies to the network manager. After the network manager fixes any discrepancies, the network manager may again select the Manage On-Line option in pop-up menu  898   o.  If there are no mis-matches between the physical device tables in the NMS database and the configuration database, then the NMS server reconciles all service provisioning data in the NMS database (or the temporary NMS database) against the service provisioning data in the configuration database. If any conflicts are discovered, the NMS server notifies the NMS client, which displays the discrepancies to the network manager. After fixing any discrepancies, the network manager may again select the Manage On-Line option in pop-up menu  898   o.    
   If there are no conflicts, the NMS server instructs the network device to stop replication between the primary configuration database within the network device and the backup configuration database within the network device. The NMS server then pushes the NMS database data into the backup configuration database, and then instructs the network device to switchover from the primary configuration database to the backup configuration database. If any errors occur after the switchover, the network device may automatically switch back to the original primary configuration database. If there are no errors, then the network device is quickly re-configured to work properly within the network. 
   Off-line configuration, therefore, provides a powerful tool to allow network managers to prepare configuration data prior to actually implementing any configuration changes. Such preparation, allows a network manager to carefully configure a network device when they have time to consider all their options and requirements, and once the network manager is ready, the configuration changes are implemented quickly and efficiently. 
   FCAPS Management: 
   Fault, Configuration, Accounting, Performance and Security (FCAPS) management are the five functional areas of network management as defined by the International Organization for Standardization (ISO). Fault management is for detecting and resolving network faults, configuration management is for configuring and upgrading the network, accounting management is for accounting and billing for network usage, performance management is for overseeing and tuning network performance, and security management is for ensuring network security. Referring to  FIG. 7   a,  GUI  895  provides a status button  899   a – 899   f  for each of the five FCAPS. By clicking on one of the status buttons, a status window appears and displays the status associated with the selected FCAPS button to the network administrator. For example, if the network administrator clicks on the F status button  899   a,  a fault event summary window  900  ( FIG. 7   b ) appears and displays the status of any faults. 
   Each FCAP button may be colored according to a hierarchical color code where, for example, green means normal operation, red indicates a serious error and yellow indicates a warning status. Today there are many NMSs that indicate faults through color coded icons or other graphics. However, current NMSs do not categorize the errors or warnings into the ISO five functional areas of network management—that is, FCAPS. 
   The color-coding and order of the FCAPS buttons provide a “status bar code” allowing a network administrator to quickly determine the category of error or warning and quickly take action to address the error or warning. 
   As with current NMSs, a network administrator may actively monitor the FCAPS buttons by sitting in front of the computer screen displaying the GUI. Unfortunately, network administrators do not have time to actively monitor the status of each network device—passive monitoring is required. To assist passive monitoring, the FCAPS buttons may be enlarged or “stretched” to fill a large portion of the screen, as shown in  FIG. 7   c.  The FCAPS buttons may be stretched in a variety of ways, for example, a stretch option in a pull down menu may be selected or a mouse may be used to drag and drop the boarders of the FCAPS buttons. Stretching the FCAPS buttons allows a network administrator to view the status of each FCAP button from a distance of 40 feet or more. Once stretched, each of the five OSI management areas can be easily monitored at a distance by looking at the bar-encoded FCAPS strip. The “stretchy FCAPS” provide instant status recognition at a distance. 
   The network administrator may set the FCAPS buttons to represent a single network device or multiple network devices or all the network devices in a particular network. Alternatively, the network administrator may have the GUI display two or more FCAPS status bars each of which represents one or more network devices. 
   Although the FCAPS buttons have been described as a string of multiple stretched bars, many different types of graphics may be used to display FCAPS status. For example, different colors may be used to represent normal operation, warnings and errors, and additional colors may be added to represent particular warnings and/or errors. Instead of a bar, each letter (e.g., F) may be stretched and color-coded. Instead of a solid color, each FCAPS button may repeatedly flash or strobe a color. For example, green FCAPS buttons may remain solid (i.e., not flashing) while red errors and yellow warnings are displayed as a flashing FCAPS button to quickly catch a network administrator&#39;s attention. As another example, green/normal operation FCAPS buttons may be a different size relative to yellow/warnings and red/errors FCAPS buttons. For example, an FCAPS button may be automatically enlarged if status changes from good operation to a warning status or an error status. In addition, the FCAPS buttons may be different sizes to allow the network administrator to distinguish between each FCAPS button from a further distance. For example, the buttons may have a graduated scale where the F button is the largest and each button is smaller down to the S button, which is the smallest. Alternatively, the F button may be the smallest while the S button is the largest, or the A button in the middle is the largest, the C and P buttons are smaller and the F and S buttons are smallest. Many variations are possible for quickly alerting a network administrator of the status of each functional area. 
   Referring to  FIG. 7   d,  for more detailed FCAPS information, the network administrator may double click the left mouse button on a particular network device (e.g., 192.168.9.201) to cause device navigation tree  898  to expand and display FCAPS branches, for example, Fault branch  898   p,  Configuration branch  898   q,  Accounting branch  898   r,  Performance branch  898   s  and Security branch  898   t.  The administrator may then select one of these branches to cause status window  897  to display tabs/folders of data corresponding to the selected branch. For example, if Fault branch  898   p  is selected ( FIG. 7   e ), an Events tab  957   a  is displayed in status window  897  as well as tab holders for other tabs (e.g., System Log tab  957   b  ( FIG. 7   f ) and Trap Destinations  957   c  ( FIG. 7   g )). If the administrator double clicks the left mouse button on the Fault branch, then device tree  898  displays a list  958   a  of the available fault tabs. The administrator may then select a tab by selecting the tab holder from status window  897  or device tree  898 . 
   Events tab  957   a  ( FIG. 7   e ) displays an event number, date, time, source, category and description of each fault associated with a module or port selected in device mimic  896   a.  System Log tab  957   b  ( FIG. 7   f ) displays an event number, date, time, source, category and description of each fault associated with the entire network device (e.g., 192.168.9.201), and Trap Destination tab  957   c  ( FIG. 7   g ) displays a system/network device IP address or DNS name, port and status corresponding to each detected trap destination. Various other tabs and formats for displaying fault information may also be provided. 
   Referring to  FIG. 7   h,  if the administrator double clicks the left mouse button on Configuration branch  898   q,  then device tree  898  expands to display a list  958   b  of available configuration sub-branches, for example, ATM protocol sub-branch  958   c,  System sub-branch  958   d  and Virtual Connections sub-branch  958   e.  When the device branch (e.g., 192.168.9.201), Configuration branch  898   q  or System branch  958   d  is selected, System tab  934 , Module tab  936 , Ports tab  938 , SONET Interface tab  940 , SONET Paths tab  942 , ATM Interfaces tab  946 , Virtual ATM Interfaces tab  947  and Virtual Connections tab  948  are displayed. These configuration tabs are described above in detail (see  FIGS. 4   s – 4   z  and  5   a – 5   z ). 
   If ATM protocol branch  958   c  is selected, then tabs/folders holding ATM protocol information are displayed, for example, Private Network-to-Network Interface (PNNI) tab  959  ( FIG. 7   i ). The PNNI tab may display PNNI cache information such as maximum path (per node), maximum entries (nodes), timer frequency (seconds), age out (seconds) and recently referenced (seconds) data. The PNNI tab may also display PNNI node information for each PNNI node such as domain name, administrative status, ATM address and node level. The PNNI cache and PNNI node information may be for a particular ATM interface, all ATM interfaces in the network device or ATM interfaces corresponding to a port or module selected by the administrator in device mimic  896   a.  Various other tabs displaying ATM information, for example, an Interim Link Management Interface (ILMI) tab, may also be provided. In addition, various other upper layer network protocol branches may be included in list  958   b,  for example, MuliProtocol Label Switching (MPLS) protocol, Frame Relay protocol or Internet Protocol (IP) branches, depending upon the capabilities of the selected network device. Moreover, various physical layer network protocol branches (and corresponding tabs) may also be included, for example, Synchronous Optical NETwork (SONET) protocol and/or Ethernet protocol branches, depending upon the capabilities of the selected network device. 
   If Virtual Connections branch  958   e  is selected, then tabs/folders holding virtual connection information are displayed, for example, Soft Permanent Virtual Circuit (PVC) tab  960   a  ( FIG. 7   j ) and Switched Virtual Circuits tab  960   b  ( FIG. 7   k ). Soft PVC tab  960   a  may display information relating to source interface, Virtual Path Identifier (VPI), Virtual Channel Identifier (VCI), status, date and time. Switched Virtual Circuits tab  960   b  may display information relating to interface, VPI, VCI, address format, address, status, date and time. The information in either tab may be for a particular virtual connection, all virtual connections in the network device or only those virtual connections corresponding to a port or module selected by the administrator in device mimic  896   a.  Various other tabs displaying virtual connection information, for example, virtual connections established through various different upper layer network protocols, may also be provided, depending upon the capabilities of the selected network device. 
   For detailed accounting information, the administrator may select Accounting branch  898   r  ( FIG. 71 ). This will cause one or more tabs/folders to be displayed which contain accounting data. For example, a Collection Setup tab  961  may be displayed that provides details on a primary and a backup archive host—that is, the system executing the Data Collection Server (described above). The Collection Setup tab may also provide statistics timer data and backup file storage data. Various other tabs displaying accounting information may also be provided. For example, a tab may be created for each particular customer to track the details of each account. 
   For detailed performance information, the administrator may select Performance branch  898   s  ( FIG. 7   m ) and double click the left mouse button to review a list  958   f  of available sub-branches, for example, ATM sub-branch  958   g,  Connections sub-branch  958   h,  Interfaces sub-branch  958   i,  System sub-branch  958   j,  and SONET sub-branch  958   k.  Selecting Performance branch  898   s  or System sub-branch  958   j  provides general performance tabs in stats window  897 , for example, System tab  962   a  and Fans tab  962   b  ( FIG. 7   n ). System tab  962   a  may provide graphical representations of various system performance parameters, for example, an odometer style graphic may be used to display CPU Utilization  962   c  and power supply voltage level  962   e  and  962   f  and a temperature gauge may be used to show Chassis Temperature  962   d.  Fans tab  962   b  may provide graphical representations of the status of the network device&#39;s fans. For example, fans may be colored green and shown spinning for normal operation, yellow and spinning for a warning status and red and not spinning for a failure status. Various other graphical representations may be used, for example, bar graphs or pie charts, and instead of graphical representations, the data may be provided in a table or other type of format. Moreover, the data in the other tabs displayed in status window  897  may also be displayed in various formats including graphical representations. 
   If the administrator selects ATM sub-branch  958   g  ( FIG. 7   o ), various tabs are displayed containing ATM related performance information, for example, ATM Stats In tab  963   a,  ATM Stats out tab  963   b  ( FIG. 7   p ), Operations Administration Maintenance (OAM) Performance tab  963   c  ( FIG. 7   q ), OAM Loopback tab  963   d  ( FIG. 7   r ), ATM Switched Virtual Circuit (SVC) In tab  963   e  ( FIG. 7   s ), ATM SVC Out tab  963   f  ( FIG. 7   t ), ATM Signaling ATM Adaptation Layer (SAAL) In tab  963   g  ( FIG. 7   u ) and ATM SAAL Out tab  963   h  ( FIG. 7   v ). The data displayed in each of these tabs may correspond to a particular ATM path (e.g., ATM-Path1 — 11/2/1), to all ATM paths corresponding to a particular port or module selected by the administrator in device mimic  896   a  or to all the ATM paths in the network device. ATM Stats In tab  963   a  ( FIG. 7   o ) and ATM Stats Out tab  963   b  ( FIG. 7   p ) may display, for example, the type, description, cells, cells per second and bits per second for each ATM path. OAM Performance tab  963   c  ( FIG. 7   q ) may display, for example, VPI, VCI, status, session type, sink source, block size and end point statistics for each ATM path, while OAM Loopback tab  963   d  ( FIG. 7   r ) may display, for example, VPI, VCI, status, send count, send trap, endpoint and flow statistics for each ATM path. ATM SVC In tab  963   e  ( FIG. 7   s ) and ATM SVC Out tab  963   f  ( FIG. 7   t ) may display, for example, type, description, total, connected, failures, last cause and setup Protocol Data Unit (PDU) data for each path, and ATM SAAL In tab  963   g  ( FIG. 7   u ) and ATM SAAL Out tab  963   h  ( FIG. 7   v ) may display, for example, type, description, errors, discards, begin PDUs, begin acknowledge, PDU begin and End PDUs for each ATM path. Various other upper layer network protocol sub-branches may also be displayed in list  958   f,  including a sub-branch for MPLS, Frame Relay and/or IP, depending upon the capabilities of the selected network device. 
   If the administrator selects Connections sub-branch  958   h  ( FIG. 7   w ), various tabs are displayed containing connection related performance information, for example, ATM Connection tab  964   a  and Priority tab  964   b  ( FIG. 7   x ). ATM Connection tab  964   a  may include, for example, connection name, transmit, receive cell loss ratio, cell discard total and throughput data for particular ATM connections. Priority tab  964   b  may include, for example, connection name, Cell Loss Priority (CLP) 0 transmit, CLP1 receive, transmit total, CLP0 receive, CLP1 receive and receive total data for particular ATM connections. The data in either tab may be for a particular selected ATM connection, each ATM connection in the network device or only those ATM connections corresponding to a particular port or module selected by the administrator in device mimic  896   a.    
   If the administrator selects Interfaces sub-branch  958   i  ( FIG. 7   y ), various tabs are displayed containing interface related performance information, for example, Interfaces tab  965 . Interfaces tab  965  may include, for example, slot and port location, description, type, speed, in octets, out octets, in errors, out errors, in discards and out discards data for particular ATM interfaces. The data in the tab may be for a particular selected ATM interface, each ATM interface in the network device or only those ATM interfaces corresponding to a particular port or module selected by the administrator in device mimic  896   a.    
   Referring to  FIG. 8   a,  if the administrator selects SONET sub-branch  958   k,  various tabs are displayed containing SONET related performance information, for example, Section tab  966   a,  Line tab  966   b  ( FIG. 8   b ) and Synchronous Transport Signal (STS) Path tab  966   c  ( FIG. 8   c ). Each of the three tabs displays a shelf/slot/port location, port descriptor, status, errored seconds, severely errored seconds and coding violation data for each port. The data may correspond to a particular port selected by the administrator, all ports in a selected module or all ports in the entire network device. Various other physical layer network protocol sub-branches may also be displayed in list  958   f,  including a sub-branch for Ethernet, depending upon the capabilities of the selected network device. 
   Referring to  FIG. 8   d,  if the administrator selects Security branch  898   t,  various tabs are displayed containing security related information, for example, Simple Network Management Protocol (SNMP) tab  967   a  and Configuration Changes tab  967   b  ( FIG. 8   e ). SNMP tab  967   a  may display, for example, read and read/write community strings and a command line interpreter (CLI) administrator password for the network device. Configuration Changes tab  967   b  may display configuration changes made to the network device including event, time, configurer and workstation identification from where the change was made. Various other security tabs may also be provided. 
   Dynamic Bulletin Boards: 
   Graphical User Interface (GUI)  895  described in detail above provides a great deal of information to a network administrator to assist the administrator in managing each network device in a telecommunications network. As shown, however, this information is contained in a large number of GUI screens/tabs. There may be many instances when a network administrator may want to simultaneously view multiple screens/tabs. To provide network managers with more control and flexibility personal application bulletin boards (PABBs, i.e., dynamic bulletin boards) are provided that allow the network administrator to customize the information they view by dragging and dropping various GUI screens/tabs (e.g., windows, table entries, dialog boxes, panels, device mimics, etc.) from GUI  895  onto one or more dynamic bulletin boards. This allows the administrator to consolidate several GUI screens and/or dialog boxes into a single view. The information in the dynamic bulletin board remains linked to the GUI such that both the GUI and the bulletin boards are dynamically updated if the screens in either the GUI or in the bulletin boards are changed. As a result, the administrator may manage and/or configure network devices through the GUI screens or the dynamic bulletin board. Within the dynamic bulletin boards, the administrator may change the format of the data and, perhaps, view the same data in multiple formats simultaneously. Moreover, the administrator may add information to one dynamic bulletin board from multiple different network devices to allow the administrator to simultaneously manage and/or configure the multiple network devices. The dynamic bulletin boards provide an alternative viewing environment, and administrators can, therefore, choose what they want to view, when they want to view it and how they want to view it. 
   Referring to  FIG. 9   a,  to open a dynamic bulletin board, a network administrator selects a Bulletin Bd option  968   a  from a view pull-down menu  968   b.  A bulletin board  970   a  ( FIG. 9   b ) is then displayed for the administrator. Instead, a bulletin board may automatically be opened whenever an administrator logs into an NMS client to access GUI  895 . Once the bulletin board is opened, the administrator may use a mouse to move a cursor over a desired GUI screen, press and hold down a left mouse button and drag the selected item onto the bulletin board (i.e., “drag and drop”). If an item within a GUI screen is capable of being dragged and dropped (i.e., posted) to the bulletin board—that is, the bulletin board supports/recognizes the GUI object—, a drag and drop icon appears as the administrator drags the cursor over to the bulletin board. If no icon appears, then the selected item is not supported by the bulletin board. Thus, the administrator is provided with visual feedback as to whether or not an item is supported by the PABB. 
   Referring to  FIG. 9   b,  as one example, an administrator may select ATM Stats In tab  963   a  corresponding to a particular network device (e.g., system 192.168.9.201) and drag and drop (indicated by arrow  969   a ) that tab onto bulletin board  970   a.  Since this is the first item dropped into the bulletin board, the ATM Stats In tab is sized and positioned to use the entire space (or a large portion of the space) dedicated to the bulletin board. Instead of selecting the entire ATM Stats In tab, the administrator may drag and drop only one or only a few entries from the tab, for example, entry  963   i,  and only those entries would then be displayed in the bulletin board. An item in bulletin board  970   a  may be removed by clicking on delete button  971   a.  The size of the bulletin board may be increased or decreased by clicking on expand button  971   b  or by selecting, dragging and dropping a bulletin board boarder (e.g.,  971   c – 971   f ), and the bulletin board may be minimized by clicking on minimize button  971   g.    
   The administrator may then select other GUI data to drag and drop onto bulletin board  970   a.  Referring to  FIG. 9   c,  for example, the administrator may select ATM Stats Out tab  963   b  also corresponding to the same network device and drag and drop (indicated by arrow  969   b ) that tab onto bulletin board  970   a.  The bulletin board automatically splits the screen to include both the ATM Stats In tab  963   a  and the ATM Stats Out tab  963   b.  Now the administrator may view both of these screens simultaneously, and since the bulletin board and the screens it displays are linked to GUI  895 , the ATM Stats In and Out tabs are automatically updated with information as the GUI itself is updated with information. Thus, if the administrator changes any data in the items dragged to the bulletin board, the GUI is automatically updated and if any data in the GUI is changed, then any corresponding screens in the bulletin board are also updated. Again, instead of selecting the entire tab, the administrator may select one or more entries in a tab and drag and drop those entries onto the bulletin board. Also, the administrator may delete any bulletin board entry by clicking on the corresponding delete button  971   a,  and change the size of any bulletin board entry using expand button  971   b  or minimize button  971   g.    
   The administrator may then select other GUI data from the same network device (e.g., system 192.168.9.201) to drag and drop to the bulletin board or the administrator may select a different network device (e.g., system 192.168.9.202,  FIG. 9   d ) in navigation tree  898  and drag and drop various GUI screens corresponding to that network device to bulletin board  970   a.  For example, the administrator may select ATM Stats In tab  972   a  and drag and drop (indicated by arrow  969   c ) that tab to bulletin board  970   a,  and the administrator may then select ATM Stats Out tab  972   b  ( FIG. 9   e ) corresponding to system 192.168.9.202 and drag and drop (indicated by arrow  969   d ) that tab onto bulletin board  970   a.  Consequently, the administrator is able to simultaneously view multiple screens corresponding to different network devices. The administrator may also choose to drag and drop related screens. For example, ATM Stats In and Out tabs  963   a,    972   a  and  963   b,    972   b,  respectively, may represent two ends of an ATM connection between the two network devices, and viewing these screens simultaneously may assist the administrator in managing both network devices. 
   As shown in  FIGS. 9   b – 9   e,  when new items are dropped onto the bulletin board, the bulletin board continues to divide the available space to fit the new items and may shrink the items to fit in the available space. Many more items may be added to a bulletin board, for example eight to ten items. However, instead of continuing to add items to the same bulletin board, the administrator may choose to open multiple bulletin boards (e.g.,  970   a – 970   n,    FIG. 9   f ). 
   An administrator may wish to view an item dragged to a bulletin board in a different format than that displayed in the GUI. The different format may, for example, have more meaning to them or provide more clarity to the task at hand. For instance, after dragging and dropping ATM Stats In tab  963   a  to bulletin board  970   a  ( FIG. 9   g ), the administrator may then move the cursor over the ATM Stats In tab and double click the right mouse button to cause a pull-down menu  973  displaying various format options to appear. A normal format option  973   a  may cause the item to appear as it did in the GUI—that is, ATM Stats In tab  963   a  will appear as shown in  FIG. 9   g.  A list format option  973   b  may cause the data in ATM Stats In tab  963   a  to be displayed as an ordered list  974   a  as shown in  FIG. 9   h.  A graph option  973   c  may cause the data in ATM Stats In tab  963   a  to be displayed as a pie chart  974   b  ( FIG. 9   i ), a bar graph  974   c  ( FIG. 9   j ) or any other type of graph or graphical representation. A config option  973   d  may cause the data in the ATM Stats In tab  963   a  to be displayed as a dialog box  974   d  ( FIG. 9   k ) displaying configuration data corresponding to a selected one of the ATM paths within the ATM Stats In tab. The data in a bulletin board entry may be displayed in a variety of different ways to make the administrator&#39;s tasks simpler and more efficient. 
   Referring to  FIG. 91 , an administrator may wish to view an item dragged to a bulletin board in multiple different formats simultaneously. For example, the administrator may move the cursor over ATM Stats In tab  963   a  in the bulletin board, press down and hold the left mouse button and drag the cursor (indicated by arrow  969   e ) over a blank area of the bulletin board (i.e., drag and drop) to add a second copy of ATM Stats In tab  963   a  to the bulletin board. The administrator may then move the cursor over the copied ATM Stats In tab, double click the right mouse button to cause pull-down menu  973  to appear and select a different format in which to display the copied ATM Stats In tab. As a result, the administrator is able to simultaneously view the normal format while also viewing another format, for example, a pie chart. 
   Although the above examples used the ATM Stats In and Out tabs, it is to be understood that any of the tabs or entries within tabs in status window  897  may be capable of being dragged and dropped into one or more dynamic bulletin boards. In addition, an administrator may drag and drop one or more of the FCAPS buttons  899   a – 899   e  ( FIG. 7   a ) to a bulletin board. 
   Referring to  FIG. 9   m,  in addition to dragging and dropping items from status window  897  or the FCAPS buttons, an administrator may drag and drop (indicated by arrow  969   f ) device mimic  896   a  onto bulletin board  970   a.  In this example, the administrator has dragged and dropped the device mimic corresponding to network device 192.168.9.201. As previously mentioned, the device mimic may display ports and modules in different colors to indicate status for those components, for example, green for normal operation, yellow for warning status and red for failure status. The administrator may then monitor the device mimic in the bulletin board while continuing to use GUI  895  for other configuration and management operations. Instead, the administrator may only select, drag and drop portions of the device mimic, for example, only one or more universal port cards or one or more forwarding cards. 
   Referring to  FIG. 9   n,  the administrator may also select a different network device in navigation tree  898  and then drag and drop (indicated by arrow  969   g ) a device mimic  975  corresponding to that device onto bulletin board  970   a.  As a result, the administrator may simultaneously view the device mimics of both network devices (or more than two network devices). In addition, the administrator may drag and drop both a front and a back view of a device mimic such that all of a network device&#39;s modules may be visible. Instead, the administrator may drag and drop a front and back view  955   a,    955   b  ( FIG. 4   n ) from a separate pull away window  955 . 
   A network administrator may save one or more dynamic bulletin boards before exiting out of the NMS client, and the NMS client may persist this data in the administrator&#39;s profile (described below). When the administrator logs in to the same or a different NMS client and selects Bulletin Bd option  968   a  ( FIG. 9   a ), their profile may automatically open up any saved dynamic bulletin boards or present the administrator with a list of saved dynamic bulletin boards that the administrator may select to have opened. When saved dynamic bulletin boards are re-opened, the NMS client updates any items posted in those bulletin boards such that the posted items are synchronized with the GUI. Instead, the NMS client may automatically open any saved dynamic bulletin boards as soon as the administrator logs on—that is, without requiring the administrator to select Bulletin Bd option  968 . 
   Through saved bulletin boards, a senior administrator may guide and instruct junior administrators through various tasks. For example, a senior administrator may drag and drop a sequence of GUI screens onto one or more bulletin boards where the sequence of GUI screens represent a series of steps that the senior administrator wants the junior administrator to take to complete a particular task (e.g., provisioning a SONET path). In addition to providing the series of steps, the senior administrator may fill in various parameters (e.g., traffic descriptors) to indicate to junior administrators the default parameters the senior administrator wants them to use. The saved bulletin board may then be added to the junior administrator&#39;s profile or put in a master profile accessible by multiple users. The junior administrator may then use a saved bulletin board to interactively complete provisioning tasks similar to the task shown in the saved bulletin board. For example, the junior administrator may use the saved SONET path bulletin board to provision one or more different SONET paths. In effect, then saved bulletin boards behave as custom wizards. 
   As described above, the dynamic bulletin boards allow a network administrator to actively monitor—simultaneously—specific information about one or more operational network devices. This provides a powerful customization tool for the administrator of large, complex network devices in large, complex telecommunications networks. By customizing views of one or more devices, the administrator may view only the data they need to see and in a format that best meets their needs. 
   Custom Object Collections: 
   As described above with respect to FCAPS management, a network device (e.g.,  10 ,  FIG. 1 and 540 ,  FIGS. 35   a – 35   b ) may include a large number (e.g., millions) of configurable/manageable objects such as modules, ports, paths, connections, etc. To provide flexibility and scalability, the network management system (NMS) allows users to create custom object collections. Thus, even though a network device or multiple network devices in a telecommunication network may include millions of objects, a network manager may create a collection and add only objects of interest to that collection. The objects may be of a similar or different type and may correspond to the same or different network devices. The network manager may also add and remove objects from existing collections, create additional new collections and remove existing collections. The network manager may then view the various objects in each collection. In addition, the collections are linked to the NMS graphical user interface (GUI), such that changes to objects in either are updated in the other. Custom object collections provide scalability and flexibility. In addition, custom object collections may be tied to user profiles to limit access. For example, a customer may be limited to viewing only the collections of objects related to their account. Similarly, a network manager may be limited to viewing only those collections of objects for which they have authority. 
   Referring to  FIG. 10   a,  when a user first logs into an NMS client by supplying a username and password, a list of network devices (e.g., 192.168.9.201 and 192.168.9.202) is displayed in accordance with the user&#39;s profile. Profiles are described in more detail below. In addition, a list of collections that correspond with the user&#39;s profile may also be provided. For example, navigation tree  898  may include a network branch  976   a,  and if the user double clicks the left mouse button on the network branch a Collections branch  976   b  is displayed. Similarly, if the user double clicks the left mouse button on the Collections branch, a list  976   c  is provided of available collections (e.g., Test 1 , New 1 , Walmart, Kmart). Alternatively or in addition, the user may select a Collections option  977   a  from a view pull-down menu  977   b  to display list  976   c  of available collections. List  976   c  may include collections pre-defined by other users (e.g., senior network administrator) and/or custom collections previously created by the user. 
   Referring to  FIG. 10   b,  to view collections that include objects corresponding to only one network device, the user may select a network device (e.g., 192.168.9.201) and select a Collections option  958   m.  If the user double clicks the left mouse button on Collections option  958   m,  a list  958   n  (e.g., Test 1  and New 1 ) of available collections corresponding to the selected network device is displayed. In addition, as the user selects various FCAPS tabs, collections containing objects from the selected tab may be displayed. For example, collection Test 1  ( FIG. 10   c ) in navigation tree  947   a  may include objects selected from Virtual ATM Interfaces tab  947  and is therefore displayed when the Virtual ATM Interfaces tab is selected. 
   Referring to  FIG. 10   d,  to add an object to an existing or new collection, a network manager first selects the object (e.g., Module object  978   a ) and then selects a Collection button  979   a  to cause an Add to Collection option  979   b  and a New Collection option  979   c  to appear. If the network manager selects New Collection option  979   c,  then a dialog box  979   d  ( FIG. 10   e ) appears and the network manager inputs the name of the new collection. After inputting the name of the new collection, the network manager selects OK button  979   e  and the object is automatically added to the collection and dialog box  979   d  is closed. If the network manager selects Add to Collection option  979   b,  a dialog box  979   f  ( FIG. 10   f ) appears listing the available collections. The user may then select one of the listed collections and then select OK button  979   g  to add the object to the collection and close dialog box  979   f.    
   Alternatively, the network manager may add an object to a collection by dragging and dropping an object from an FCAPs tab onto a collection branch in a navigation tree. Referring to  FIG. 10   g,  for example, a network manager may select an object  978   b  by pressing down on the left mouse button, dragging (indicated by arrows  980   a  and  980   b ) the object to a collection and dropping the object on the collection (i.e., drag and drop). 
   For instance, object  978   b  may be dragged and dropped on collection Test 1  in either navigation tree  947   a  or  898 . An object may also be dragged and dropped into a named collection in a pull down menu or dialog box. 
   When a collection is selected by a network manager, customer or other user, for example, by double clicking on the collection name in a navigation tree or pull down menu, the tabs in service status window  897  are changed to include only objects in the selected collection. For instance, if the collection includes only SONET path objects, then only the SONET Paths tab will include objects once the collection is selected and all other tabs will not include any objects. Alternatively, the other tabs in service status window  897  may include objects corresponding to or related to the objects in the selected collection. 
   Referring to  FIG. 10   h,  when device 192.168.9.201 is selected and the SONET Paths tab is selected, a large number of SONET paths may be displayed. Referring to  FIG. 10   i,  when collection New 1  is selected, the SONET Paths Tab is changed to display only those SONET path objects within the New 1  collection. As a result, the user need only view the objects in which they are interested. 
   To remove an object from a collection, the network manager selects an object and then selects a Remove button  982 . The network manager may also select an object and double click the left mouse button to cause a dialog box to appear. The network manager may edit certain parameters and then exit from the dialog box. Any changes made to an object in a collection are automatically updated in GUI  895 . Similarly, any changes made to an object in GUI  895  are automatically updated in any and all collections including that object. 
   Custom object collections allow a user to view only those objects that are of interest. These may be a few objects from an otherwise very large object list in the same FCAPS tab (that is, the collection acts as a filter), and these may be a few objects from different FCAPS tabs (that is, the collection acts as an aggregator). Consequently, both flexibility and scalability are provided through custom object collections. 
   Custom object collections may also be used to restrict access to network objects. For example, a senior network administrator may establish a collection of objects and provide access to that collection to a junior network manager through the junior network manager&#39;s profile. In one embodiment, the junior network manager may not be provided with the full navigation tree  898  ( FIG. 10   a ) after logging in. Instead, only a list of available collections may be provided. Thus, the junior network manager&#39;s access to the network is limited to the objects contained in the available collections and the FCAPS tabs will similarly only include those same objects. 
   Similarly, collections may be created that include objects corresponding to a particular customer, for example, Walmart or Kmart. A customer profile may be established for each customer and one or more collections containing only objects relevant to each customer may be assigned to the relevant customer profile. Consequently, each customer is limited to viewing only those objects corresponding to their own accounts and not the accounts of any other customers. This permits Customer Network Management (CNM) without breaching the security provided to each customer account. 
   Profiles: 
   Profiles may be used by the NMS client to provide individual users (e.g., network managers and customers) with customized graphical user interfaces (GUIs) or views of their network and with defined management capabilities. For example, some network managers are only responsible for a certain set of devices in the network. Displaying all network devices makes their management tasks more difficult and may inadvertently provide them with management capabilities over network devices for which they are not responsible or authorized to perform. With respect to customers, profiles limit access to only those network device resources in a particular customer&#39;s network—that is, only those network device resources for which the customer has subscribed/paid. This is crucial to protecting the proprietary nature of each customer&#39;s network. Profiles also allow each network manager and customer to customize the GUI into a presentation format that is most efficient or easy for them to use. For example, even two users with access to the same network devices and having the same management capabilities may have different GUI customizations through their profiles. In addition, profiles may be used to provide other important information, for example, SNMP community strings to allow an NMS server to communicate with a network device over SNMP, SNMP retry and timeout values, and which NMS servers to use, for example, primary and secondary servers may be identified. 
   A network administrator is typically someone who powers up a network device for the first time, installs necessary software on the new network device as well as installs any NMS software on an NMS computer system, and adds any additional hardware and/or software to a network device. The network administrator is also the person that attaches physical network cables to network device ports. The first time GUI  895  is displayed to a network administrator, an NMS client application uses a default profile including a set of default values. Referring again to  FIG. 7   a,  the administrator may change the default values in his profile by selecting (e.g., clicking on) a profile selection  902  in a navigation tree menu  898 . This causes the NMS client to display a profiles tab  903  ( FIG. 11   a ) on the screen. The profile tab displays any existing profiles  904 . The first time the profile tab appears only the network administrator&#39;s profile is displayed as no other profiles yet exist. 
   To save a network manager&#39;s time, the profiles tab may also include a copy button  906 . By selecting a profile  904  and clicking on the copy button, an existing profile is copied. The network manager may then change the parameters within the copied profile. This is helpful where two user profiles are to include the same or similar parameters. 
   To change the parameters in the network administrator&#39;s profile or any other existing profile, including a copied profile, the user double clicks on one of the profiles  904 . To add a new profile, the user clicks on an Add button  905 . In either case, the NMS client displays a profile dialog box  907  ( FIGS. 11   b – 11   c ) on the screen. Through the profile dialog box, a user&#39;s user name  908   a,  password  908   b  and confirmed password  908   c  may be added or changed. The confirm password field is used to assure that the password was entered properly in the password field. The password and confirmed password may be encrypted strings used for user authentication. These fields will be displayed as asterisks on the screen. Once added, a user simply logs on to an NMS client with this user name and password and the NMS client displays the GUI in accordance with the other parameters of this profile. 
   A group level access field  908   d  enables/disables various management capabilities (i.e., functionality available through the NMS client). Clicking on the group level access field may provide a list of available access levels. In one embodiment, access levels may include administrator, provisioner and viewer (e.g., customer), with administrator having the highest level of management capabilities and viewer having the lowest level of management capabilities (described in more detail below). In one embodiment, users can create profiles for other users at or below their own group access level. For example, a user at the provisioner access level can create user profiles for users at either the provisioner or viewer level but cannot create an administrator user profile. 
   A description may be added in a description field  908   e,  including, for example, a description of the user, phone number, fax number and/or e-mail address. A group name may be added to group field  908   f,  and a list of network device IP addresses may be provided in a device list field  908   g.  Alternatively, a domain name server (DNS) name may be provided and a host look up may be used to access the IP address of the corresponding device. Where a group name is provided, the list of network devices is associated with the group such that if the same group name is assigned to multiple user profiles, the users will be presented with the same view—that is, the same list of network devices in device list field  908   g.  For example, users from the same customer may share a group name corresponding to that customer. A wildcard feature is available for the group field. For example, perhaps an * or ALL may be used as a wildcard to indicate that a particular user is authorized to see all network devices. In most instances, the wildcard feature will only be used for a high-level network administrator. The list of devices indicates which network devices the user may manage or view, for example, configuration status and statistics data may be viewed. 
   Within a profile certain policy flags (i.e., attributes) may also be set. For example, a flag  908   h  may be set to indicate that the user is not allowed to change his/her password, and an account disable flag  908   i  may be set to disable a particular profile/account. In addition, a flag  908   j  may be set to allow the user to add network device IP addresses to device list field  908   g,  and a number may be added to a timeout field  908   k  to specify a number of minutes after which a user will be automatically logged out due to inactivity. A zero in this field or no value in this field may be used to indicate unlimited activity, that is, the user will never be automatically logged out. 
   The profile may also be used to indicate with which NMS servers the NMS client should communicate. An IP address or DNS name may be added to a primary server field  908   l  and a secondary server field  908   m.  If the primary server fails, the client will access the secondary server. A port number may be added to primary server port field  908   n  and to secondary server port field  908   o  to indicate the particular ports that should be used for RMI connectivity to the primary and secondary NMS servers. 
   As described below, the information provided in a user profile is stored in tables within the NMS database, and when a user logs onto the network through an NMS client, the NMS client connects to an NMS server that retrieves the user&#39;s profile information and sends the information to the NMS client. The NMS client automatically saves the NMS server primary and secondary IP addresses and port numbers from the user&#39;s profile to a team session file associated with the user&#39;s username and password in a memory  986  ( FIG. 11   y ) local to the NMS client. If the user logs into an NMS client through a web browser, then the NMS client may save the NMS server primary and secondary IP addresses and port numbers to a cookie that is then stored in the user&#39;s local hard drive. The next time the user logs in to the NMS client, the NMS client uses the IP addresses and port numbers stored in the team session file or cookie to connect to the appropriate NMS server. 
   The first time a user accesses an NMS client, however, no team session file or cookie will be available. Consequently, during the initial access of the NMS client, the NMS client may use a default IP address to connect with an NMS server or a pop-up menu  1034  ( FIG. 11   z ) may be displayed in which the user may type in the IP address in a field  1034   a  of the NMS server they want the NMS client to use or select an IP address from a pop-up menu that appears when a dropdown button  1034   b  is selected. 
   User profiles and team session files/cookies allow a network administrator or provisioner to push down new NMS server IP addresses, port numbers and other information to users simply by changing those values in the user profiles. For example, an NMS server may be over loaded and a network administrator may wish to move some users from this NMS server to another less utilized NMS server. The administrator need only change the NMS server IP addresses and port numbers in the users&#39; profiles to affect the switch. The NMS server sends the new IP addresses and port numbers to the one or more NMS clients through which the users are logged in, and the NMS clients save the new IP addresses and port numbers in each user&#39;s team session file or cookie. The next time the users log in, the NMS client(s) use the new IP addresses and port numbers in the team session files or cookies to access the appropriate NMS server. Thus, the users selected by the administrator are automatically moved to a different NMS server without the need to notify those users or take additional steps. In addition to saving IP addresses and perhaps port numbers in team session files/cookies, other information from the user profile may also be saved in team session files/cookies and changes to that information may be pushed down by the administrator simply by changing a user profile. 
   Referring again to  FIGS. 11   b – 11   c,  additional fields may be added to device list  908   g  to provide more information. For example, a read field  908   p  may be used to indicate the SNMP community string to be used to allow the NMS server to communicate with the network device over SNMP. The SNMP connection may be used to retrieve statistical data and device status from the network device. In addition, a read/write field  908   q  may be used to indicate an SNMP community string to allow the NMS server to configure the network device and/or provision services. The profile may also include a retry field  908   r  and a timeout field  908   s  to provide SNMP retry and timeout values. Many different fields may be provided in a profile. 
   Instead of providing all the parameters and fields in a single profile dialog box, they may be separated into a variety of a tabbed dialog boxes ( FIGS. 11   d – 11   g ). The tabbed dialog boxes may provide better scalability and flexibility for future needs. 
   In one embodiment, an administrator level user has both read and write access to the physical and logical objects of the NMS client. Thus, all screens and functionality are available to an administrator level user, and an administrator after physically attaching an external network attachment to a particular network device port may then enable that port and provision SONET paths on that port. All screens are available to a provisioner level user, however, they do not have access to all functionality as they are limited to read-only access of physical objects. For example, a provisioner can see SONET ports available on a device and can provision SONET paths on a port, but the provisioner cannot enable/disable a SONET port. In other words, a provisioner&#39;s power begins at the start of logical objects (not physical objects), for example, SONET paths, ATM interfaces, virtual ATM interfaces, and PVCs, and continues through all the configuration aspects of any object or entity that can be stacked on top of either a SONET path or ATM interface. A viewer (e.g., customer) level user has read-only access to logical entities and only those logical entities corresponding to their group name or listed in the device list field. A viewer may or may not have access to Fault, Configuration, Accounting, and Security categories of FCAPS relative to their devices. 
   A customer may install an NMS client at a customer site or, preferably, the customer will use a web browser to access the NMS client. To use the web browser, a service provider gives the customer an IP address corresponding to the service provider&#39;s site. The customer supplies the IP address to their web browser and while at the service provider site, the customer logs in with their username and password. The NMS client then displays the customer level GUI corresponding to that username and password. 
   Referring to  FIG. 11   h,  a user preference dialog box  909  may be used to customize the GUI into a presentation format that is most efficient or easy for a user to work with. For example, show flags (i.e., attributes) may be used to add tool tips (flag  910   a ), add horizontal grid lines on tables (flag  910   b ), add vertical grid lines on tables (flag  910   c ) and add bookmarks/short cuts (e.g., create a short cut to a PVC dialog box). Look and feel flags may also be used to make the GUI appear as a JAVA GUI would appear (flag  911   a ) or as a native application, for example, Windows, Windows/NT or Motif, GUI would appear (flag  911   b ). 
   As an alternative to providing a Group Name  908   f  ( FIGS. 11   b – 11   c ) or a Customer Name ( FIG. 11   d ), when a profile is created or changed the administrator or provisioner may double click the left mouse button on a network device (e.g., 192.168.9.202,  FIGS. 11   b – 11   c  or  11   g ) in the device list to cause a pop-up menu  1000  ( FIGS. 11   i – 11   j ) to be displayed. The pop-up menu provides a list  1000   a  of available groups corresponding to the selected network device, and the administrator or provisioner may select one or more groups (e.g., Walmart-East, Walmart-West) from the list for which the user corresponding to profile will be authorized to access. 
   Each group may include one or more configured resources (e.g., SONET paths, VATM interfaces, ATM PVCs) within the network device, and the resources in each group may be related in some way. For instance, a group may include resources configured by a particular provisioner. As another example, a group may include configured resources purchased by a particular customer. For instance, Walmart Corporation may be a customer of a network service provider and each network device resource paid for/subscribed to by Walmart may be included in a Walmart group. In addition, if Walmart subscribes to a larger number of configured resources, the network service provider may create several groups within the same network device for Walmart, for example, Walmart-East may include network device resources associated with Walmart activities in the eastern half of the United States and Walmart-West may include network device resources associated with Walmart activities in the western half of the United States. In addition, the network service provider may create a Walmart-Total group including all configured resources within the network device paid for by Walmart. Various users may be given access to one or more groups. For example, a Walmart employee responsible for network service in the eastern half of the United States may be given access to only the Walmart-East group while another higher level Walmart employee is given access to both the Walmart-East and Walmart-West groups. In addition, the same group name may be used in multiple network devices to simplify tracking. Through profiles multiple users may be given access to the same or different groups of configured resources within each network device, and users may be given access to multiple groups of configured resources in different network devices. 
   When an administrator or a provisioner configures a network device resource, they may assign that resource to a particular group. For example, when an administrator or provisioner configures one or more SONET paths, they may assign each SONET path to a particular group. Referring to  FIG. 11   k – 11   m,  within a SONET Path configuration wizard  1002 , an administrator or provisioner may select a SONET Path within the SONET path table  1002   a  and type in a group name in field  1002   b  or select a group name from a pop-up menu displayed when dropdown button  1002   c  is selected. When the administrator/provisioner selects OK button  1002   d  or Modify button  1002   e,  the NMS client sends the SONET path data to the NMS server. The NMS server uses this data to fill in a SONET path table (e.g.,  600 ′,  FIGS. 11   y  and  60   g ) in configuration database  42 . A new row is added to the SONET path table for each newly configured SONET path, and data in existing rows are modified for modified SONET paths. 
   In addition, the NMS server searches a Managed Resource Group table  1008  ( FIGS. 11   n – 11   y ) within the configuration database for a match with each assigned group name. If no match is found for a group name, indicating the group name represents a new group, then the NMS server adds a row to the Managed Resource Group table, and the NMS server assigns the group an LID (e.g.,  1145 ) and inserts the LID into an LID column  1008   a.  The NMS server also inserts the Managed Device PID (e.g., 1) from column  983   b  in Managed Device table  983  ( FIGS. 11   y  and  60   a ) in the configuration database into a column  1008   b  and inserts the group name in column  1008   c.    
   The NMS server also uses the SONET path data from the NMS client to add a row in a Managed Resource Table  1007  ( FIGS. 11   o  and  11   y ) in configuration database  42  for each newly configured SONET path or to modify data in existing rows for modified SONET paths. The NMS server assigns an LID (e.g., 4443) to each row and inserts the assigned LID into a column  1007   a.  The NMS server then inserts the assigned SONET path LID (e.g.,  901 ) from Path LID column  600   a  ( FIG. 60   g ) in the SONET path table into a Resource LID column  1007   b.  The NMS server also inserts the assigned group LID (e.g.,  1145 ) from column  1008   a  in Managed Resource Group table  1008  ( FIG. 11   n ) into a managed resource group LID column  1007   c.    
   Just as each SONET path may be assigned to a group, each other type of configured resource/manageable entity within the network device may be assigned to a group. For example, when an administrator or provisioner configures a virtual ATM (VATM) interface, they may also assign the VATM interface to a group. Referring to  FIG. 11   p,  within an Add V-ATM Interface dialog box  1004 , an administrator or provisioner may type in a group name in a field  1004   a  or select a group name from a pop-up menu displayed when expansion button  1004   b  is selected. As another example, when an administrator or provisioner configures an ATM PVC, they may assign the ATM PVC to a particular group. Referring to  FIG. 11   q,  in a virtual connection wizard  1006 , the administrator or provisioner may assign an ATM PVC to a group by typing in a group name in a field  1006   a  or by selecting a group name from a pop-up menu displayed when expansion button (e.g., Group List)  1006   b  is selected. Again, when the administrator or provisioner selects OK button  1004   c  ( FIG. 11   p ) or Finish button  1006   c  ( FIG. 11   q ), the NMS client sends the relevant data to the NMS server. The NMS server updates Virtual ATM Interface table  993  ( FIG. 60   j ), a Virtual Connection table  994  ( FIG. 60   k ), Virtual Link table  995  ( FIG. 60L ) and Cross-Connect table  996  ( FIG. 60   m ), as described below, and similar to the actions taken for the configured SONET paths, the NMS server adds a row to Managed Resource Group table  1008  ( FIG. 11   n ) for each new group and a row to Managed Resource table  1007  ( FIG. 11   o ) for each new managed resource—that is, for each new VATM interface and for each new ATM PVC. This same process may be used to add any manageable entity to a group. 
   Instead of using a Managed Resource Group table and a Managed Resource table, the configured network device resource tables (e.g., SONET path table, Virtual ATM IF table, etc.) could include a group name field. However, the Managed Resource Group adds a layer of abstraction, which may allow each configured resource to belong to multiple groups. Moreover, the Managed Resource table provides scalability and modularity by not being tied to a particular resource type. That is, the Managed Resource table will include a row for each different type of configured resource and if the network device is upgraded to include new types of configurable resources, they too may be added to the Managed Resource table without having to upgrade other processes. If each configurable resource is limited to belonging to only one group, then the Managed Resource Table  1007  ( FIG. 11   o ) may include only Resource LID  1007   b  and not LID  1007   a.    
   Referring again to  FIGS. 11   b – 11   h,  after adding or changing a user profile, the administrator or provisioner selects OK button  908   t.  Selection of the OK button causes the NMS client (e.g., NMS client  850   a,    FIG. 11   y ) to send the information provided in the dialog box (or boxes) to an NMS server (e.g., NMS server  851   a ), and the NMS server uses the received information to update various tables in NMS database  61 . In one embodiment, for a newly added user, the NMS server assigns a unique logical identification number (LID) to the user and adds a new row in a User table  1010  ( FIGS. 11   r  and  11   y ) in the NMS database including the assigned LID  1010   a  and the username  1010   b,  password  1010   c  and group access level  1010   d  provided by the NMS client. For example, the NMS server may add a new row  1010   e  including an assigned user LID of  2012 , a username of Dave, a password of Marble and a group access level of provisioner. 
   The NMS server also adds a row to a User Managed Device table  1012  ( FIGS. 11   s  and  11   y ) for each network device listed in the user profile. For each row, the NMS server assigns a user managed device LID (e.g., 7892) and inserts it in an LID column  1012   a.  The NMS server also inserts a user LID  1012   b,  a host LID  1012   c,  a retry value  1012   d  and a timeout value  1012   e.  The inserted retry and timeout values are from the user profile information sent from the NMS client. The user LID  1012   b  includes the previously assigned user LID (e.g.,  2012 ) from column  1010   a  of User Table  1010 . The host LID is retrieved from an Administration Managed Device table  1014  ( FIGS. 11   t  and  11   y ). 
   The Administration Managed Device table includes a row for each network device (i.e., managed device) in the telecommunications network. To add a network device to the network, an administrator selects an Add Device option in a pop-up menu  898   c  ( FIG. 6   a ) in GUI  895  to cause dialog box  1013  ( FIG. 11   u ) to be displayed. The administrator enters the intended IP address or DNS name (e.g., 192.168.9.202) of the new network device into a device host field  1013   a  and may also enter a device port (e.g.,  1521 ) into a device port field  1013   b.  The administrator also adds SNMP retry  1013   c  and timeout  1013   d  values, which may be overridden later by values supplied within each user profile. In addition, the administrator adds a password for each user access level. In one embodiment, the administrator adds an administrator password  1013   e,  a provisioner password  1013   f  and a viewer password  1013   g  for the managed device. 
   The Administration Managed Device table, therefore, provides a centralized set of device records shared by all NMS servers, and since the records are centralized, the Administration Managed Device table facilitates centralized changes to the devices in the network. For example, a network device may be added to the network by adding a record and removed from the network by deleting a record. As another example, a network device&#39;s parameters (e.g., IP address) may be changed by modifying data in a record. Because the changes are made to centralized records accessed by all NMS servers, no change notifications need to be sent and the NMS servers may automatically receive the changed data during the next access of the table. Alternatively, the NMS server that makes a change to the central database may send notices out to each connected NMS client and other NMS servers in the network. 
   For newly added devices, after the information is input in the dialog box, the administrator selects an Add button  1013   h  causing the NMS client to send the data from the dialog box to the NMS server. Similarly, for changes to device data, after the information is changed in the dialog box, the administrator selects an OK button  1013   i  to cause the NMS client to send the data from the dialog box to the NMS server. For new devices, the NMS server uses the received information to add a row to Administration Managed Device table  1014  in NMS database  61 , and for existing devices, the NMS server uses the received information to update a previously entered row in the Administration Managed Device table. For each managed device/row, the NMS server assigns a host LID (e.g.,  9046 ) and inserts it in LID column  1014   a.    
   When the NMS server adds a new row to the User Managed Device table  1012  ( FIG. 11   s ), corresponding to a managed device in a user profile, the NMS server searches column  1014   b  in the Administration Managed Device table  1014  for a host address matching the IP address (e.g., 192.168.9.202) provided in the user profile information sent from the NMS client. When a match is found, the NMS server retrieves the host LID (e.g.,  9046 ) from column  1014   a  and inserts it in host LID column  1012   c  in the User Managed Device table. 
   After receiving user profile information from an NMS client, the NMS server also updates a User Resource Group Map table  1016  ( FIGS. 11   v  and  11   y ) in NMS database  61 . For each group identified in the user profile information—one or more groups may be selected in each Group List dialog box  1000  associated with each network device in the user profile—the NMS server adds a row to the User Resource Group Map table. The NMS server assigns an LID (e.g.,  8086 ) for each row and inserts the LID in a column  1016   a.  The NMS server then inserts the User LID (e.g.,  2012 ) into User LID column  1016   b  from User table  1010  column  1010   a  corresponding to the user profile. In addition, the NMS server inserts a User Resource Group LID into column  1016   c.    
   For each group name received by the NMS server, the NMS server searches a User Resource Group table  1018  ( FIGS. 11   w  and  11   y ), group name column  1018   c,  for a match. If a match is not found, then the group is a new group, and the NMS server adds a row to the User Resource Group table. The NMS server assigns an LID (e.g.,  1024 ) to each row and inserts the assigned LID into an LID column  1018   a.  This User Resource Group LID is also added to column  1016   c  in the User Resource Group Map table  1016  ( FIG. 11   v ). Within the User Resource Group table  1018  ( FIG. 11   w ), the NMS server also inserts the network device&#39;s host LID in a column  1018   b  from Administration Managed Device table  1014  ( FIG. 11   t ), column  1014   a,  and the NMS server inserts the group name (e.g., Walmart-East) in column  1018   c.  Through the group name, the User Resource Group table in the NMS database provides for dynamic binding with the Managed Resource Group table  1008  ( FIG. 11   n ) in the configuration database, as described below. 
   After a user&#39;s profile is created, the user may log in through an NMS client (e.g.,  850   a,    FIG. 11   y ) by typing in their username and password. The NMS client then sends the username and password to an NMS server (e.g.,  851   a ), and in response, the NMS server sends a query to NMS database  61  to search User table  1010  ( FIG. 11   r ) column  1010   b  for a username matching the username provided by the NMS client. If the username is not found, then the user is denied access. If the username is found, then, for additional security, the NMS server may compare the password provided by the NMS client to the password stored in column  1010   c  of the User table. If the passwords do not match, then the user is denied access. If the passwords match, then the NMS server creates a user profile logical managed object (LMO). 
   In one embodiment, the user profile LMO is a JAVA object and a JAVA persistence layer within the NMS server creates the user profile LMO. For each persistent JAVA class/object, metadata is stored in a class table  1020  ( FIG. 11   y ) within the NMS database. Thus, the JAVA persistence layer within the NMS server begins by retrieving metadata from the class table in the NMS database corresponding to the user profile LMO. The metadata may include simple attributes and association attributes. 
   Referring to  FIG. 11   x,  the metadata for a user profile LMO  1022  includes three simple attributes—username  1022   a,  password  1022   b  and group access level  1022   c —and two association attributes—resource group maps  1022   d  and managed devices  1022   e.  The NMS server inserts the username (e.g., Dave), password (e.g., Marble) and group access level (e.g., provisioner) retrieved from the User table  1010  into the user profile LMO  1024  ( FIG. 11   y ) being created. The managed devices association attribute  1022   e  causes the NMS server to create a user managed device properties LMO  1026  for each network device in the user&#39;s profile. 
   The NMS server first retrieves metadata from class table  1020  associated with the user managed device properties LMO  1026 . The metadata includes two simple attributes (retry  1026   b  and timeout  1026   c ) and one association attribute (managed device  1026   a ). The metadata causes the NMS server to search User Managed Device table  1012  ( FIG. 11   s ) column  1012   b  for a user LID (e.g.,  2012 ) corresponding to the user LID in column  1010   a  ( FIG. 11   r ) of User table  1010  in a row  1010   e  associated with the username and password received from the NMS client. For each row in the User Managed Device table having the matching user LID (e.g.,  2012 ), the NMS server creates a user managed device properties LMO  1026  and inserts the retry value from column  1012   d  as the retry simple attribute  1026   b  and the timeout value from column  1012   e  as the timeout simple attribute  1026   c.    
   In response to the managed device associated attribute, the NMS server retrieves metadata from class table  1020  associated with administration managed device properties LMO  1028 . The metadata includes a list of simple attributes including host address  1028   a,  port address  1028   b,  SNMP retry value  1028   c,  SNMP timeout value  1028   d  and a database port address  1028   e  for connecting to the configuration database within the network device. The metadata also includes simple attributes corresponding to passwords for each of the possible group access levels, for example, an administrator password  1028   f,  a provisioner password  1028   g  and a viewer password  1028   h.    
   The NMS server uses the host LID (e.g.,  9046 ) from column  1012   c  in the User Managed Device table ( FIG. 11   s ) as a primary key to locate the row (e.g.,  1014   c,    FIG. 11   t ) in the Administration Managed Device table  1014  corresponding to the network device. The NMS server uses the data in this table row to insert values for the simple attributes in the Administration Managed Device LMO  1028 . For example, a host address of 192.168.9.202 and a port address of  1521  may be inserted. The NMS server also selects a password corresponding to the user&#39;s group access level. For instance, if the user&#39;s group access level is provisioner, then the NMS server inserts the provisioner password of, for example, team 2 , from column  1014   d  into the Administration Managed Device LMO. 
   The NMS server then inserts the newly created Administration Managed Device LMO  1028  into the corresponding User Managed Device Properties LMO  1026 , and the NMS server also inserts each newly created User Managed Devices Properties LMO  1026  into User Profile LMO  1022 . Thus, the information necessary for connecting to each network device listed in the user profile is made available within user LMO  1022 . 
   The resource group maps association attribute  1022   d  ( FIG. 11   x ) within user LMO  1022  causes the NMS server to create a user resource group map LMO  1030  for each group in the user&#39;s profile. The user resource group map LMO  1030  includes one simple attribute—user profile  1030   a —and one association attribute—user resource group  1030   b.  The NMS server inserts the user LID (e.g.,  2012 ) corresponding to the user LID in column  1010   a  ( FIG. 11   r ) in User table  1010  associated with the username, password and group access level received from the NMS client. 
   In response to user resource group associated attribute  1030   b,  the NMS server creates a User Resource Group LMO  1032 . The NMS server begins by retrieving metadata from class table  1020  corresponding to the User Resource Group LMO. The metadata includes three simple attributes: host address  1032   a,  port address  1032   b  and group name  1032   c.  The NMS server searches User Resource Group Map table  1016  ( FIG. 11   y ) for the user LID (e.g.,  2012 ) corresponding to the username and password received from the NMS client. The NMS server then uses the corresponding user resource group LID (e.g.,  1024 ) from column  1016   c  as a primary key to locate a row (e.g.,  1018   d,    FIG. 11   w ) in User Resource Group table  1018 . The NMS server inserts the group name (e.g., Walmart-East) from the located row in User Resource Group table  1018  as simple attribute  1032   c  in user resource group LMO  1032 . The NMS server then uses the host LID (e.g.,  9046 ) from the located row to search column  1014   a  in the Administration Managed Device table  1014  ( FIG. 11   t ) for a match. Once a match is found, the NMS server uses data in the located row (e.g.,  1014   c ) to insert the host address (e.g., 192.168.9.202) from column  1014   b  as simple attribute  1032   a  and the port address (e.g.,  1521 ) from column  1014   e  as simple attribute  1032   b  in user resource group LMO  1032 . The NMS server then inserts the user resource group LMO  1032  into the user resource group map LMO  1030 , and the NMS server inserts each of the user resource group map LMOs  1030  into the user profile LMO  1022 . Thus, the data (e.g., host and port address and group name) required to locate each group included in the user profile is inserted within user profile LMO  1022 . 
   The NMS server sends data from the user profile LMO to the NMS client to allow the NMS client to present the user with a graphical user interface such as GUI  895  shown in  FIG. 4   a.  If the user selects one of the network devices listed in navigation tree  898 , the NMS server retrieves the group level access (e.g., provisioner) and the password (e.g., team  2 ) corresponding to that group level access from the user profile LMO and then connects to the selected network device. The NMS server then retrieves the network device&#39;s physical data as described below under the heading “NMS Server Scalability.” 
   Alternatively, a more robust set of data may be sent from the NMS server to the NMS client such that for each transaction issued by the NMS client, the data provided with the transaction eliminates the need for the NMS server to access the user profile LMO in its local memory. This reduces the workload of the NMS server, which will likely be sent transactions from many NMS clients. In one embodiment, the NMS server may send the NMS client the entire user profile LMO. Instead, the server may create a separate client user profile LMO that may present the data in a format expected by the NMS client and perhaps include only some of the data from the user profile LMO stored locally to the NMS server. In the preferred embodiment, the client user profile LMO includes at least data corresponding to each device in the user profile and each group selected within the user profile for each device. If the user selects one of the network devices listed in navigation tree  898 , the NMS client includes the selected network device&#39;s IP address, the password corresponding to the user&#39;s group access level and the database port number in the “Get Network Device” transaction sent to the NMS server. The NMS server uses this information to connect to the network device and return the network device&#39;s physical data to the NMS client. 
   If the user selects a tab in configuration status window  897  that includes logical data corresponding to configured network device resources (e.g., SONET Paths tab  942  ( FIG. 5   q ), ATM Interfaces tab  946  ( FIG. 5   r ), Virtual ATM Interfaces tab  947  ( FIG. 5   s ), Virtual Connections tab  948  ( FIG. 5   z )), then the NMS server searches the user profile LMO for group names corresponding to the selected network device or the NMS client provides the group names in the transaction. The NMS server then retrieves data from the selected network device for configured resources corresponding to each group name and the selected tab. If no group names are listed, the NMS server may retrieve data for all configured resources corresponding to the selected tab. 
   For example, if a user selects SONET Paths tab  942  ( FIG. 5   q ), then the NMS server searches the user profile LMO for all group names corresponding to the selected network device (e.g., Walmart-East) or the NMS client provides all group names (e.g., Walmart-East) corresponding to the selected network device to the NMS server as part of the “Get SONET paths” transaction. The NMS server then dynamically issues a where clause such as “where SONET path is in group Walmart-East”. This causes group name column  1008   c  in the Managed Resource Group table  1008  ( FIG. 11   n ) in the network device&#39;s configuration database  42  to be searched for a match with the group name of Walmart-East. Additional where clauses may be dynamically issued corresponding to other group names found in the user profile LMO. If no match is found for a group name in column  1008   c,  then the NMS server simply returns an empty set to the NMS client. If a match is found for a group name (e.g., Walmart-East), then the NMS server retrieves the managed resource group LID (e.g.,  1145 ) from column  1008   a  in the same row (e.g., row  1008   d ) as the matching group name. 
   The NMS server then searches column  1007   c  in the Managed Resource table  1007  ( FIG. 11   o ) for one or more matches with the retrieved managed resource group LID (e.g.,  1145 ). As described above, the Managed Resource Table includes one row for each configured network device resource in a particular group. For each match found for the retrieved managed resource group LID (e.g.,  1145 ), the NMS server uses the resource LID (e.g.,  901 ) from column  1007   b  as a primary key to a row in a table including the data corresponding to the configured resource. In this example, a resource LID of  901  corresponds to a row in SONET Path Table  600 ′ ( FIG. 60   g ). Since the user selected the SONET Paths tab, the NMS server retrieves the data in the corresponding row and sends it to the NMS client. The NMS client uses the data to update graphical user interface (GUI) tables  985  in local memory  986 , which causes GUI  895  to display the SONET path to the user. Other SONET paths may also be included in the group Walmart-East, and those would be similarly located and retrieved by the NMS server and sent to the NMS client for display to the user. 
   Since each group may include different types of configured resources, the NMS server may locate configured resources other than SONET paths, for example, VATMs or ATM PVCs, in Managed Resource table  1007 . If configured resources are found that do not correspond to the tab selected by the user, the NMS server does not retrieve the associated data or send it to the NMS client. The NMS server follows a similar process if the user selects another tab including logical data, for example, ATM Interfaces tab  946  ( FIG. 5   r ), Virtual ATM Interfaces tab  947  ( FIG. 5   s ) or Virtual Connections tab  948  ( FIG. 5   z ). Although the above discussion has used SONET paths, VATM interfaces and ATM PVCs as examples of configurable resources that may be included in a group, other configurable resources may also be included, for example, configurable resources corresponding to different layer one or upper layer network protocols (e.g., Ethernet, MPLS, Frame Relay, IP). 
   When data is stored in tables within the same database, references from one table to another may provide a direct binding and referential integrity may be maintained by only deleting the upper most record—that is, not leaving any dangling records. Referential integrity prevents references from being orphaned, which may lead to data loss or other more severe problems, such as a system crash. In the current embodiment, tables are stored across multiple databases. Certain tables are stored in NMS database  61  and certain other tables are stored in the configuration database within each network device in the network. Direct binding between tables cannot be maintained since a database may be removed or a record deleted without maintaining referential integrity. To address this issue, group names are used to provide a “dynamic binding” between the User Resource Group table  1018  ( FIG. 11   w ) in the NMS database and the Managed Resource Group table  1008  ( FIG. 11   n ) in each configuration database. Since there is no direct binding, if a group name is not found in the Managed Resource Group table, the NMS server simply returns an empty set and no data is lost or other more serious problems caused. If the group name is later added to the Managed Resource Group table, then through dynamic binding, it will be found. 
   Through a user profile, a user may log-on to the network with a single, secure username and password through any NMS client, access any network device in their user profile and access configured resources corresponding to groups in their user profile. Since the tables including the data necessary for the creation of user profile LMOs are stored in the NMS database, any NMS server capable of connecting to the NMS database—that is, any NMS server in the network—may access the tables and generate a user LMO. As a result, users may log-on with a single, secure username and password through any NMS client that may be connected to an NMS server capable of connecting to the NMS database. Essentially, users may log on through any computer system/workstation (e.g.,  984 ,  FIG. 11   y ) on which an NMS client is loaded or remotely through internet web access to an NMS client within the network and gain access to the network devices listed in their user profile. Thus, each user need only remember a single username and password to configure/manage any of the network devices listed in their user profile or any of the resources included within groups listed in their user profile through any NMS client in the network. 
   In addition, user profiles provide a level of indirection to better protect the passwords used to access each network device. For example, access to the passwords may be limited to only those users capable of adding network devices to the network, for example, users with the administrator group access level. Other users would not see the passwords since they are automatically added to their user profile LMO, which is not accessible by users. The level of indirection provided by user profiles also allows network device passwords to be easily changed across the entire network. Periodically the passwords for access to the network devices in a network may be changed for security. The network device passwords may be quickly changed in the Administration Managed Device table  1014  ( FIG. 11   t ), and due to the use of profiles, each user does not need to be notified of the password changes. The new passwords will be utilized automatically each time users log in. This provides for increased scalability since thousands of users will not need to be notified of the new passwords. Moreover, if a rogue user is identified, they can be quickly prevented from further access to the network through any NMS client by simply changing the user&#39;s username and/or password in the user&#39;s profile or by deleting the user&#39;s profile. Changing the username and/or password in the user profile would cause the NMS server to change the data in user table  1010  ( FIG. 11   r ), and deleting a user profile would cause the NMS server to remove the corresponding row in the User table. In either case, the user would no longer be able to log in. 
   User profiles and group names also simplify network management tasks. For example, if an administrator adds a newly configured resource to a group, all users having access to that group will automatically be able to access the newly configured resource. The administrator need not send out a notice or take other steps to update each user. 
   Group names in a user profile define what the user can view. For instance, one customer may not view the configured resources subscribed for by another customer if their resources are assigned to different groups. Thus, groups allow for a granular way to “slice” up each network device according to its resources. 
   The user access level in a user profile determines how the NMS server behaves and affects what the user can do. For example, the viewer user access level provides the user with read-only capability and, thus, prevents the NMS server from modifying data in tables. In addition, the user access level may be used to restrict access—even read access—to certain tables or columns in certain tables. 
   Network Device Power-Up: 
   Referring again to  FIG. 1 , on power-up, reset or reboot, the processor on each board (central processor and each line card) downloads and executes boot-strap code (i.e., minimal instances of the kernel software) and power-up diagnostic test code from its local memory subsystem. After passing the power-up tests, processor  24  on central processor  12  then downloads kernel software  20  from persistent storage  21  Into non-persistent memory in memory subsystem  28 . Kernel software  20  includes operating system (OS), system services (SS) and modular system services (MSS). 
   In one embodiment, the operating system software and system services software are the OSE operating system and system services from Enea OSE Systems, Inc. in Dallas, Tex. The OSE operating system is a pre-emptive multi-tasking operating system that provides a set of services that together support the development of distributed applications (i.e., dynamic loading). The OSE approach uses a layered architecture that builds a high level set of services around kernel primitives. The operating system, system services, and modular system services provide support for the creation and management of processes; inter-process communication (IPC) through a process-to-process messaging model; standard semaphore creation and manipulation services; the ability to locate and communicate with a process regardless of its location in the system; the ability to determine when another process has terminated; and the ability to locate the provider of a service by name. 
   These services support the construction of a distributed system wherein applications can be located by name and processes can use a single form of communication regardless of their location. By using these services, distributed applications may be designed to allow services to transparently move from one location to another such as during a fail over. 
   The OSE operating system and system services provide a single inter-process communications mechanism that allows processes to communicate regardless of their location in the system. OSE IPC differs from the traditional IPC model in that there are no explicit IPC queues to be managed by the application. Instead each process is assigned a unique process identification that all IPC messages use. Because OSE IPC supports inter-board communication the process identification includes a path component. Processes locate each other by performing an OSE Hunt call on the process identification. The Hunt call will return the Process ID of the process that maps to the specified path/name. Inter-board communication is carried over some number of communication links. Each link interface is assigned to an OSE Link Handler. The path component of a process path/name is the concatenation of the Link Handler names that one must transverse in order to reach the process. 
   In addition, the OSE operating system includes memory management that supports a “protected memory model”. The protected memory model dedicates a memory block (i.e., defined memory space) to each process and erects “walls” around each memory block to prevent access by processes outside the “wall”. This prevents one process from corrupting the memory space used by another process. For example, a corrupt software memory pointer in a first process may incorrectly point to the memory space of a second processor and cause the first process to corrupt the second processor&#39;s memory space. The protected memory model prevents the first process with the corrupted memory pointer from corrupting the memory space or block assigned to the second process. As a result, if a process fails, only the memory block assigned to that process is assumed corrupted while the remaining memory space is considered uncorrupted. 
   The modular software architecture takes advantage of the isolation provided to each process (e.g., device driver or application) by the protected memory model. Because each process is assigned a unique or separate protected memory block, processes may be started, upgraded or restarted independently of other processes. 
   Referring to  FIG. 12   a,  the main modular system service that controls the operation of computer system  10  is a System Resiliency Manager (SRM). Also within modular system services is a Master Control Driver (MCD) that learns the physical characteristics of the particular computer system on which it is running, in this instance, computer system  10 . The MCD and the SRM are distributed applications. A master SRM  36  and a master MCD  38  are executed by central processor  12  while slave SRMs  37   a – 37   n  and slave MCDs  39   a – 39   n  are executed on each board (central processor  12  and each line card  16   a – 16   n ). The SRM and MCD work together and use their assigned view ids and APIs to load the appropriate software drivers on each board and to configure computer system  10 . 
   Also within the modular system services is a configuration service program  35  that downloads a configuration database program  42  and its corresponding DDL file from persistent storage into non-persistent memory  40  on central processor  12 . In one embodiment, configuration database  42  is a Polyhedra database from Polyhedra, Inc. in the United Kingdom. 
   Hardware Inventory and Set-Up: 
   Referring to  FIG. 12   a,  when computer system  10  is first powered up, a mission kernel image executable file (MKI.exe)  50  for central processor card  12  is bootstrap loaded from persistent storage, for example, an EPROM, located on the central processor card. MKI  50  starts MCD Master  38  and a local MCD slave  39   a.  MCD slave  39   a  reads a card type and version number out of local persistent storage, for example, EPROM  42 , and passes this information to Master MCD  38 . 
   Master MCD  38  begins by taking a physical inventory of computer system  10  (over the I 2 C bus) and assigning a unique physical identification number (PID) to each item. 
   Despite the name, the PID is a logical number unrelated to any physical aspect of the component being numbered. In one embodiment, pull-down/pull-up resistors on the chassis mid-plane provide the number space of Slot Identifiers. The master MCD may read a register for each slot, including the slot for central processor card  12 , that allows it to get the bit pattern produced by these resistors. MCD  38  assigns a unique PID to the chassis, each shelf in the chassis, each slot in each shelf, each card (e.g., central processor  12 , line cards  16   a – 16   n ) inserted in each slot, and, for certain line cards, each port on each line card. (Other items or components may also be inventoried.) 
   Typically, the number of cards and ports in a computer system is variable but the number of chassis, shelves and slots is fixed. Consequently, a PID could be permanently assigned to the chassis, shelves and slots and stored in a file. To add flexibility, however, MCD  38  assigns a PID even to the chassis, shelves and slots to allow the modular software architecture to be ported to another computer system with a different physical a construction (i.e., multiple chassis and/or a different number of shelves and slots) without having to change the PID numbering scheme. 
   Referring also to  FIGS. 12   b – 12   c,  for each card (e.g., line card  16   a – 16   n ), except central processor card  12 , in computer system  10 , MCD  38  communicates with a diagnostic program (DP)  40   a – 40   n  being executed by the card&#39;s processor to learn each card&#39;s type and version. The diagnostic program reads a card type and version number out of persistent storage, for example, EPROM  42   a – 42   n,  and passes this information to the MCD. For example, line cards  16   a  and  16   b  could be cards that implement Asynchronous Transfer Mode (ATM) protocol over Synchronous Optical Network (SONET) protocol as indicated by a particular card type, e.g., 0XF002, and line card  16   e  could be a card that implements Internet Protocol (IP) over SONET as indicated by a different card type, e.g., 0XE002. In addition, line card  16   a  could be a version three ATM over SONET card meaning that it includes four SONET ports  44   a – 44   d  each of which may be connected to an external SONET optical fiber that carries an OC-48 stream, as indicated by a particular port type 00620, while line card  16   b  may be a version four ATM over SONET card meaning that it includes sixteen SONET ports  46   a – 46   f  each of which carries an OC-3 stream as indicated by a particular port type, e.g.,  00820 . Other information is also passed to the MCD by the DP, for example, diagnostic test pass/fail status. With this information and the card type and version number provided by slave MCD  39   a , MCD  38  creates card table (CT)  47  and port table (PT)  49  in configuration database  42 . As described below, the configuration database copies all changes to an NMS database. If the MCD cannot communicate with the diagnostic program to learn the card type and version number, then the MCD assumes the slot is empty. 
   Even after initial power-up, master MCD  38  will continue to take physical inventories to determine if hardware has been added or removed from computer system  10 . For example, cards may be added to empty slots or removed from slots. When changes are detected, master MCD  38  will update CT  47  and PT  49  accordingly. 
   For each card except the central processor card, master MCD  38  searches a physical module description (PMD) file  48  in memory  40  for a record that matches the card type and version number retrieved from that card. The PMD file may include multiple files. The PMD file includes a table that corresponds card type and version number with the name of the mission kernel image executable file (MKI.exe) that needs to be loaded on that card. Once determined, master MCD  38  passes the name of each MKI executable file to master SRM  36 . Master SRM  36  requests a bootserver (not shown) to download the MKI executable files  50   a – 50   n  from persistent storage  21  into memory  40  (i.e., dynamic loading) and passes each MKI executable file  50   a – 50   n  to a bootloader (not shown) running on each board (central processor and each line card). The bootloaders execute the received MKI executable file. 
   Instead of having a single central processor card (e.g.,  12 ,  FIG. 1 ), the external control functions and the internal control functions may be separated onto different cards as described in U.S. patent application Ser. No. 09/574,343, filed May 20, 2000 and entitled “Functional Separation of Internal and External Controls in Network Devices”, which is hereby incorporated herein by reference. As shown in  FIGS. 41   a  and  41   b,  the chassis may support primary and backup internal control (IC) processor cards  542   a  and  543   a  and primary and backup external control (EC) processor cards  542   b  and  543   b.  In this case, Master MCD  38  is a primary Master MCD and is executed on one of the processor cards, for example, IC processor card  542   a,  and a backup Master MCD is executed on the backup processor card, for example, IC processor card  543   a.  Master MCD  38  then detects and treats the other processor cards, for example, EC processor cards  542   b  and  543   b,  the same as the other cards (e.g., port cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h,  forwarding cards  546   a – 546   e,    548   a – 548   e,    550   a – 550   e,    552   a – 552   e,  switch fabric cards  570   a – 570   b,  cross connection cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b,    568   a – 568   b ). That is, the Master MCD reads the card type and version out of an EPROM located on each external processor card. The Master MCD then enters this information in CT  47  and uses the PMD file to determine the name of the MKI.exe corresponding to that card type and version. Again the Master MCD passes this name to the Master SRM which causes the bootserver to download the MKI and pass the MKI to bootloaders running on each external processor card. 
   Referring again to  FIG. 12   a,  the MKIs executed by each card start slave MCDs (e.g.,  39   a – 39   n ) on each card. The slave MCDs may also read the card type and version from their local EPROMs and send the information to the Master MCD. The Master MCD can then confirm this information against the information it previously loaded in CT  47  and PT  49 . 
   Once the cards are executing the appropriate MKI, the slave MCDs (e.g.,  39   a – 39   n ) and slave SRMs (e.g.,  37   a – 37   n ) on each card download executable files corresponding to each card. Referring to  FIG. 13   a,  for example, slave MCDs (e.g.,  39   a – 39   n ) search PMD file  48  in memory  40  on central processor  12  for a match with their line card type and version number. Just as the master MCD  38  found the name of the MKI executable file for each line card in the PMD file, each slave MCD reads the PMD file to learn the process names of all the executable files (e.g., device drivers, SONET, ATM, MPLS, etc.) associated with each card type and version. The slave MCDs provide these names to the slave SRMs on their cards. Slave SRMs  37   a – 37   n  then download and execute the executable files (e.g., device drivers, DD.exe  56   a – 56   n ) from memory  40 . As one example, one port device driver  43   a – 43   d  may be started for each port  44   a – 44   d  on line card  16   a.  The port driver and port are linked together through the assigned port PID number. Unique process names are listed in the PMD file for each port driver to be started on line card  16   a.    
   In order to understand the significance of the PMD file (i.e., metadata), note that the MCD software does not have knowledge of card types built into it. Instead, the MCD parameterizes its operations on a particular card by looking up the card type and version number in the PMD file and acting accordingly. Consequently, the MCD software does not need to be modified, rebuilt, tested and distributed with new hardware. The changes required in the software system infrastructure to support new hardware are simpler, modify logical model  280  ( FIGS. 3   a – 3   b ) to include: a new entry in the PMD file (or a new PMD file) and, where necessary, new device drivers and applications. Because the MCD software, which resides in the kernel, will not need to be modified, the new applications and device drivers and the new DDL files (reflecting the new PMD file) for the configuration database and NMS database are downloaded and upgraded (as described below) without re-booting the computer system (hot upgrade). 
   Network Management System (NMS): 
   Referring to  FIG. 13   b,  as described above, a user/network administrator of computer system  10  works with network management system (NMS) software  60  to configure computer system  10 . In the embodiment described below, NMS  60  runs on a personal computer or workstation  62  and communicates with central processor  12  over Ethernet network  41  (out-of-band). Instead, the NMS may communicate with central processor  12  over data path  34  ( FIG. 1 , in-band). Alternatively (or in addition as a back-up communication port), a user may communicate with computer system  10  through a console interface/terminal ( 840 ,  FIG. 2   a ) connected to a serial line  66  connecting to the data or control path using a command line interface (CLI) protocol. Instead, NMS  60  could run directly on computer system  10  provided computer system  10  has an input mechanism for the user. 
   During installation, an NMS database  61  is established on, for example, work-station  62  using a DDL executable file corresponding to the NMS database. The DDL file may be downloaded from persistent storage  21  in computer system  10  or supplied separately with other NMS programs as part of an NMS installation kit. The NMS database mirrors the configuration database through an active query feature (described below). In one embodiment, the NMS database is an Oracle database from Oracle Corporation in Boston, Mass. 
   The NMS and central processor  12  pass control and data over Ethernet  41  using, for example, the Java Database Connectivity (JDBC) protocol. Use of the JDBC protocol allows the NMS to communicate with the configuration database in the same manner that it communicates with its own internal storage mechanisms, including the NMS database. Changes made to the configuration database are passed to the NMS database to ensure that both databases store the same data. This synchronization process is much more efficient, less error-prone and timely than older methods that require the NMS to periodically poll the network device to determine whether configuration changes have been made. In these systems, NMS polling is unnecessary and wasteful if the configuration has not been changed. Additionally, if a configuration change is made through some other means, for example, a command line interface, and not through the NMS, the NMS will not be updated until the next poll, and if the network device crashes prior to the NMS poll, then the configuration change will be lost. In computer system  10 , however, command line interface changes made to configuration database  42  are passed immediately to the NMS database through the active query feature ensuring that the NMS, through both the configuration database and NMS database, is immediately aware of any configuration changes. 
   Asynchronously Providing Network Device Management Data: 
   Typically, work-station  62  ( FIG. 13   b ) is coupled to many network computer systems, and NMS  60  is used to configure and manage each of these systems. In addition to configuring each system, the NMS also interprets management data gathered by each system relevant to each system&#39;s network accounting data, statistics, security and fault logging (or some portion thereof) and presents this to the user. In current systems, two distributed carefully synchronized processes are used to move data from a network system/device to the NMS. The processes are synchronized with each other by having one or both processes maintain the state of the other process. To avoid the problems associated with using two synchronized processes, in the present invention, internal network device management subsystem processes are made asynchronous with external management processes. That is, neither the internal nor external processes maintain each other&#39;s state and all processes operate independently of the other processes. This also minimizes or prevents data loss (i.e., lossless system), which is especially important for revenue generating accounting systems. 
   In addition, instead of having the NMS interpret each network device&#39;s management data in the same fashion, flexibility is added by having each system send the NMS (e.g., data collector server  857 ,  FIG. 2   a ) class files  410  including compiled source code indicating how its management data should be interpreted. Thus, the NMS effectively “learns” how to process (and perhaps display) management data from the network device via the class file. Through the reliable File Transfer Protocol (FTP), management subsystem processes  412  ( FIG. 13   b ) running on central processor  12  push data summary files  414  and binary data files  416  to the NMS. Each data summary file indicates the name of the class file the NMS should use to interpret a corresponding binary data file. If the computer system has not already done so, it pushes the class file to the NMS. In one embodiment, the management subsystem processes, class files and NMS processes are JAVA programs, and JAVA Reflection is used to dynamically load the data-specific application class file and process the data in the binary data file. As a result, a new class file can be added or updated on a network device without having to reboot or upgrade the network device or the NMS. The computer system simply pushes the new class file to the NMS. In addition, the NMS can use different class files for each network device such that the data gathered on each device can be particularized to each device. 
   Referring to  FIG. 13   c,  in one embodiment, the management subsystem  412  ( FIG. 13   b ) is broken into two pieces: a usage data server (UDS)  412   a  and a file transfer protocol (FTP) client  412   b.  The UDS is executed on internal processor control card  542   a  (see also  FIGS. 41   b  and  42   a – 42   b ) while the FTP client is executed on external processor control card  542   b  (see also  FIGS. 41   a  and  42   a – 42   b ). Alternatively, in a network device with one processor control card or a central processor control card, both the UDS and FTP client may be executed on that one card. When each device driver, for example, SONET driver  415   a – 415   n  and ATM driver  417   a – 417   n  (only SONET driver  415   a  and ATM driver  417   a  are shown for convenience and it is to be understood that multiple drivers may be present on each card), within network device  540  is built, it links in a usage data monitoring library (UDML). 
   When device drivers are first started, upgraded or re-booted, the device driver makes a call into the UDML to notify the UDML as to which statistical data the device driver is able to gather. For example, an ATM device driver may be able to gather virtual circuit (VC) accounting statistics and Virtual ATM (VATM) interface statistics while a SONET device driver may be able to gather SONET statistics. The device driver then makes a call into the UDML to notify the UDML as to each interface (including virtual circuits) for which the device driver will be gathering data and the types of data the device driver will provide for each interface. 
   The UDML sends a registration packet to the UDS providing one or more string names corresponding to the types of data that the UDML will send to the UDS. For example, for ATM drivers the UDML may register “Acct_PVC” to track permanent virtual circuit statistics, “Acct_SVC” to track soft permanent virtual circuit statistics, “Vir_Intf” to track quality of service (QoS) statistics corresponding to virtual interfaces, and “Bw_Util” to track bandwidth utilization. As another example, for SONET drivers the UDML may register “Section” to track section statistics, “Line” to track line statistics and “Path” to track path statistics. The UDML need only register each string name with the UDS once, for example, for the first interface registered, and not for each interface since the UDML will package up the data from multiple interfaces corresponding to the same string name before sending the data with the appropriate string name to the UDS. 
   The UDML includes a polling timer to cause each driver to periodically poll its hardware for “current” statistical/accounting data samples  411   a.  The current data samples are typically gathered on a frequent interval of, for example, 15 minutes, as specified by the polling timer. The UDML also causes each driver to put the binary data in a particular format, time stamp the data and store the current data sample locally. When a current data sample for each interface managed by the device driver and corresponding to a particular string name is stored locally, the UDML packages all of the current data samples corresponding to the same string name into one or more packets containing binary data and sends the packets to the UDS with the registered string name. 
   In addition, the UDML adds each gathered current data sample  411   a  to a local data summary  411   b.  The UDML clears the data summary periodically, for example, every twenty-four hours, and then adds newly gathered current data samples to the cleared data summary. Thus, the data summary represents an accumulation of current data samples gathered over the period (e.g., 24 hours). 
   The UDS maintains a list of UDMLs expected to send current data samples and data summaries corresponding to each string name. For each poll, the UDS combines the data sent from each UDML with the same string name into a common binary data file (e.g., binary data files  416   a – 416   n ) associated with that string name in non-volatile memory, for example, a hard drive  421  located on internal control processor  542   a.  When all UDMLs in the list corresponding to a particular string name have reported their current data samples or data summaries, the UDS closes the common data file, thus ending the data collecting period. Preferably, the data is maintained in binary form to keep the data files smaller than translating it into other forms such as ASCII. Smaller binary files require less space to store and less bandwidth to transfer. 
   If after a predetermined period of time has passed, for example, 5 minutes, one or more of the UDMLs in a list has not sent binary data with the corresponding string name, the UDS closes the common data file, ending the data collecting period. The UDS then sends a notice to the non-responsive UDML(s). The UDS will repeat this sequence a predetermined number of times, for example, three, and if no binary data with the corresponding string name is received, the UDS will delete the UDML(s) from the list and send a trap to the NMS indicating which specific UDML is not responsive. As a result, maintaining the list of UDMLs that will be sending data corresponding to each string name allows the UDS to know when to close each common data file and also allows the UDS to notify the NMS when a UDML becomes non-responsive. This provides for increased availability including fault tolerance—that is, a fault on one card or in one application cannot interrupt the statistics gathering from each of the other cards or other applications on one card—and also including hot swapping where a card and its local UDMLs may no longer be inserted within the network device. 
   Since a large number of UDMLs may be sending data to the UDS, the potential exists for the data transfer rate to the UDS to be larger than the amount of data that the UDS can process and larger than local buffering can support. Such a situation may result in lost data or worse, for example, a network device crash. A need exists, therefore, to be able to “throttle” the amount of data being sent from the UDMLs to the UDS depending upon the current backlog of data at the UDS. 
   In one embodiment, the UDML is allowed to send up to a maximum number of packets to the UDS before the UDML must wait for an acknowledge (ACK) packet from the UDS. For example, the UDML may be allowed to send three packets of data to the UDS and in the third packet the UDML must include an acknowledge request. Alternatively, the UDML may follow the third packet with a separate packet including an acknowledge request. Once the third packet is sent, the UDML must delay sending any additional packets to the UDS until an acknowledge packet is received from the UDS. The UDML may negotiate the maximum number of packets that can be sent in its initial registration with the UDS. Otherwise, a default value may be used. 
   Many packets may be required to completely transfer a binary current data sample or data summary to the UDS. Once the acknowledge packet is received, the UDML may again send up to the maximum number (e.g., 3) of packets to the UDS again including an acknowledge request in the last packet. Requiring the UDML to wait for an acknowledge packet from the UDS, allows the UDS to throttle back the data received from UDMLs when the UDS has a large backlog of data to process. 
   A simple mechanism to accomplish this throttling is to have the UDS send an acknowledge packet each time it processes a packet containing an acknowledge request. Since the UDS is processing the packet that is a good indication that it is steadily processing packets. If the number of packets received by the UDS is large, it will take longer to process the packets and, thus, longer to process packets containing acknowledge requests. Thus, the UDMLs must wait longer to send more packets. On the other hand, if the number of packets is small, the UDS will quickly process each packet received and more quickly send back the acknowledge request and the UDMLs will not have to wait as long to send more packets. 
   Instead of immediately returning an acknowledge packet when the UDS processes a packet containing an acknowledge request, the UDS may first compare the number of packets waiting to be processed against a predetermined threshold. If the number of packets waiting to be processed is less than the predetermined threshold, then the UDS immediately sends the acknowledge packet to the UDML. If the number of packets waiting to be processed is more than the predetermined threshold, then the UDS may delay sending the acknowledge packet until enough packets have been processed that the number of packets waiting to be processed is reduced to less than the predetermined threshold. Instead, the UDS may estimate the amount of time that it will need to process enough packets to reduce the number of packets waiting to be processed to less than the threshold and send an acknowledge packet to the UDML including a future time at which the UDML may again send packets. In other words, the UDS does not wait until the backlog is diminished to notify the UDMLs but instead notifies the UDMLs prior to reducing the backlog and based on an estimate of when the backlog will be diminished. 
   Another embodiment for a throttling mechanism requires polls for different statistical data to be scheduled at different times to load balance the amount of statistical traffic across the control plane. For example, the UDML for each ATM driver polls and sends data to the UDS corresponding to PVC accounting statistics (i.e., Acct_PVC) at a first time, the UDML for each ATM driver polls and sends data to the UDS corresponding to SPVC accounting statistics (i.e., Acct_SPVC) at a second time, and the UDML for each ATM driver and each SONET driver polls and sends data to the UDS corresponding to other statistics at other times. This may be accomplished by having multiple polling timers within the UDML corresponding to the type of data being gathered. Load balancing and staggered reporting provides distributed data throttling which may smooth out control plane bandwidth utilization (i.e., prevent large data bursts) and reduce data buffering and data loss. 
   Referring to  FIG. 13   d,  instead of having each device driver on a card package the binary data and send it to the UDS, a separate, low priority packaging program (PP)  413   a – 413   n  may be resident on each card and responsible for packaging the binary statistical management data from each device driver and sending it to the UDS. Running the PP as a lower priority program ensures that processor cycles are not taken away from time-critical processes. Load balancing and staggered reporting may still be accomplished by having each PP send acknowledge requests in the last of a predetermined number of packets and wait for the UDS to send an acknowledge packet as described above. 
   As mentioned, the UDML causes the device driver to periodically gather the current statistical management data samples for each interface and corresponding to each string name. The period may be relatively frequent, for example, every 15 minutes. In addition, the UDML causes the device driver or separate packaging program to add the current data sample to a data summary corresponding to the same string name each time a current data sample is gathered. The UDML clears the data summary periodically, for example, every twenty-four hours. To reduce bandwidth utilization, the data summary and corresponding string name is sent to the UDS periodically but with an infrequent time period of, for example, every 6 to 12 hours. The data summary provides resiliency such that if any of the current data samples are lost in any of the various transfers, the data summary is still available. Local resiliency may be provided by storing a backlog of both current data sample files and summary data files in hard drive  421 . For example, the four most recent current data sample files and the two most recent summary data files corresponding to each string name may be stored. 
   If FTP client  412   b  cannot send data from hard drive  421  to file system  425  for a predetermined period of time, for example, 15 minutes, the FTP client may notify the UDS and the UDS may notify each UDML. Each UDML then continues to cause the device driver to gather current statistical management data samples and add them to the data summaries at the same periodic interval (i.e., current data interval, e.g., 15 minutes), however, the UDML stops sending the current data samples to the UDS. Instead, the UDML sends only the data summaries to the UDS but at the more frequent current data interval (e.g., 15 minutes) instead of the longer time period (e.g., 6 to 12 hours). The UDS may then update the data summaries stored in hard drive  421  and cease collecting and storing current data samples. This will save space in the hard drive and minimize any data loss. 
   To reduce the amount of statistical management data being transferred to the UDS, a network manager may selectively configure only certain of the applications (e.g., device drivers) and certain of the interfaces to provide this data. As each UDML registers with the UDS, the UDS may then inform each UDML with respect to each interface as to whether or not statistical management data should be gathered and sent to the UDS. There may be many circumstances in which gathering this data is unnecessary. For example, each ATM device driver may manage multiple virtual interfaces (VATMs) and within each VATM there may be several virtual circuits. A network manager may choose not to receive statistics for virtual circuits on which a customer has ordered only Variable Bit Rate (VBR) real time (VBR-rt) and VBR non-real time (VBR-nrt) service. For VBR-rt and VBR-nrt, the network service provider may provide the customer only with available/extra bandwidth and charge a simple flat fee per month. However, a network manager may need to receive statistics for virtual circuits on which a customer has ordered a high quality of service such as Constant Bit Rate (CBR) to ensure that the customer is getting the appropriate level of service and to appropriately charge the customer. In addition, a network manager may want to receive statistics for virtual circuits on which a customer has ordered Unspecified Bit Rate (UJBR) service to police the customer&#39;s usage and ensure they are not receiving more network bandwidth than what they are paying for. Allowing a network manager to indicate that certain applications or certain interfaces managed by an application (e.g., a VATM) need not provide statistical management data or some portion of that data to the UDS reduces the amount of data transferred to the UDS—that is, reduces internal bandwidth utilization—, reduces the amount of storage space required in the hard drive, and reduces the processing power required to transfer the statistical management data from remote cards to external file system  425 . 
   For each binary data file, the UDS creates a data summary file (e.g., data summary files  414   a – 414   n ) and stores it in, for example, hard drive  421 . The data summary file defines the binary file format, including the type based on the string name, the length, the number of records and the version number. The UDS does not need to understand the binary data sent to it by each of the device drivers. The UDS need only combine data corresponding to similar string names into the same file and create a summary file based on the string name and the amount of data in the binary data file. The version number is passed to the UDS by the device driver, and the UDS includes the version number in the data summary file. 
   Periodically, FTP client  412   b  asynchronously reads each binary data file and corresponding data summary file from hard drive  421 . Preferably, the FTP client reads these files from the hard drive through an out-of-band Ethernet connection, for example, Ethernet  32  ( FIG. 1 ). Alternatively, the FTP client may read these files through an in-band data path  34  ( FIG. 1 ). The FTP client then uses an FTP push to send the binary data file to a file system  425  accessible by the data collector server and, preferably local to the data collector server. The FTP client then uses another FTP push to send the data summary file to the local file system. Since binary data files may be very long and an FTP push of a binary data file may take some time, the data collector server may periodically search the local file system for data summary files. The data collector server may then attempt to open a discovered data summary file. If the data collector server is able to open the file, then that indicates that the FTP push of the data summary file is complete, and since the data summary file is pushed after the binary data file, the data collector server&#39;s ability to open the data summary file may be used as an indication that a new binary data file has been completely received. Since data summary files are much smaller than binary data files, having the data collector server look for and attempt to open data summary files instead of binary data files minimizes the thread wait within the data collector server. 
   In one embodiment, the data collector server is a JAVA program, and each different type of binary data file has a corresponding JAVA class file (e.g., class file  410   a ) that defines how the data collector server should process the binary data file. When a device driver is loaded into the network device, a corresponding JAVA class file is also loaded and stored in hard drive  421 . The FTP client periodically polls the hard drive for new JAVA class files and uses an FTP push to send them to file system  425 . The data collector server uses the binary file type in the data summary file to determine which JAVA class file it should use to interpret the binary data file. The data collector server then converts the binary data into ASCII or AMA/BAF format and stores the ASCII or AMA/BAF files in the file system. The data collector server may use a set of worker threads for concurrency. 
   As described, the data collector server is completely independent of and asynchronous with the FTP client, which is also independent and asynchronous of the UDS. The separation of the data collector server and FTP client avoids data loss due to process synchronization problems, since there is no synchronization, and reduces the burden on the network device by not requiring the network device to maintain synchronization between the processes. In addition, if the data collector server goes down or is busy for some time, the FTP client and UDS continue working and continue sending binary data files and data summary files to the file system. When the data collector server is again available, it simply accesses the data summary files and processes the binary files as described above. Thus, there is no data loss and the limited storage capacity within the network device is not strained by storing data until the data collector server is available. In addition, if the FTP client or UDS goes down, the data collector server may continue working. 
   An NMS server (e.g., NMS server  851   a ), which may or may not be executing on the same computer system  62  as the data collector server, may periodically retrieve the ASCII or AMA/BAF files from the file system. The files may represent accounting, statistics, security, logging and/or other types of data gathered from hardware within the network device. The NMS server may also access the corresponding class files from the file system to learn how the data should be presented to a user, for example, how a graphical user interface (GUI) should be displayed, what data and format to display, or perhaps which one of many GUIs should be used. The NMS server may use the data to, for example, monitor network device performance, including quality of service guarantees and service level agreements, as well as bill customers for network usage. Alternatively, a separate billing server  423   a  or statistics server  423   b,  which may or may not be executing on the same computer system  62  as the data collector server and/or the NMS server, may periodically retrieve the ASCII or AMA/BAF files from the file system in order to monitor network device performance, including quality of service guarantees and service level agreements, and/or bill customers for network usage. One or more of the data collector server, the NMS server, the billing server and the statistics server may be combined into one server. Moreover, management files created by the data collector server may be combined with data from the configuration or NMS databases to generate billing records for each of the network provider&#39;s customers. 
   The data collector server may convert the ASCII or AMA/BAF files into other data formats, for example, Excel spread sheets, for use by the NMS server, billing server and/or statistics server. In addition, the application class file for each data type may be modified to go beyond conversion, including direct integration into a database or an OSS system. For example, many OSS systems use a Portal billing system available from Portal Software, Inc. in Cupertino, Calif. The JAVA class file associated with a particular binary data file and data summary file may cause the data collector server to convert the binary data file into ASCII data and then issue a Portal API call to give the ASCII data directly to the Portal billing system. As a result, accounting, statistics, logging and/or security data may be directly integrated into any other process, including third party processes, through JAVA class files. 
   Through JAVA class files, new device drivers may be added to a network device without having to change UDS  412   a  or FTP client  412   b  and without having to re-boot the network device and without having to upgrade/modify external processes. For example, a new forwarding card (e.g., forwarding card  552   a ) may be added to an operating network device and this new forwarding card may support MPLS. An MPLS device driver  419 , linked within the UDML, is downloaded to the network device as well as a corresponding class file (e.g., class file  410   e ). When the FTP client discovers the new class file in hard drive  421 , it uses an FTP push to send it to file system  425 . The FTP client does not need to understand the data within the class file it simply needs to push it to the file system. Just as with other device drivers, the UDML causes the MPLS driver to register appropriate string names with the UDS and poll and send data to the UDS with a registered string name. The UDS stores binary data files (e.g., binary data file  416   e ) and corresponding data summary files (e.g., data summary file  414   e ) in the hard drive without having to understand the data within the binary data file. The FTP client then pushes these files to the file system again without having to understand the data. When the data summary file is discovered by the data collector server, the data collector server uses the binary file type in the data summary file to locate the new MPLS class file  410   e  in the file system and then uses the class file to convert the binary data in the corresponding binary data file into ASCII format and perhaps other data formats. Thus, a new device driver is added and statistical information may be gathered without having to change any of the other software and without having to re-boot the network device. 
   As described, having the data collector server be completely independent of and asynchronous with the FTP client avoids the typical problems encountered when internal and external management programs are synchronized. Moreover, modularity of device drivers and internal management programs is maintained by providing metadata through class files that instruct the external management programs as to how the management data should be processed. Consequently, device drivers may be modified, upgraded and added to an operating network device without disrupting the operation of any of the other device drivers or the management programs. 
   Configuration: 
   As described above, unlike a monolithic software architecture which is directly linked to the hardware of the computer system on which it runs, a modular software architecture includes independent applications that are significantly decoupled from the hardware through the use of a logical model of the computer system. Using the logical model and a code generation system, a view id and API are generated for each application to define each application&#39;s access to particular data in a configuration database and programming interfaces between the different applications. The configuration database is established using a data definition language (DDL) file also generated by the code generation system from the logical model. As a result, there is only a limited connection between the computer system&#39;s software and hardware, which allows for multiple versions of the same application to run on the computer system simultaneously and different types of applications to run simultaneously on the computer system. In addition, while the computer system is running, application upgrades and downgrades may be executed without affecting other applications and new hardware and software may be added to the system also without affecting other applications. 
   Referring again to  FIG. 13   b,  initially, NMS  60  reads card table  47  and port table  49  to determine what hardware is available in computer system  10 . The NMS assigns a logical identification number (LID)  98  ( FIGS. 14   b  and  14   c ) to each card and port and inserts these numbers in an LID to PID Card table (LPCT)  100  and an LID to PID Port table (LPPT)  101  in configuration database  42 . Alternatively, the NMS could use the PID previously assigned to each board by the MCD. However, to allow for hardware redundancy, the NMS assigns an LID and may associate the LID with at least two PIDs, a primary PID  102  and a backup PID  104 . (LPCT  100  may include multiple backup PID fields to allow more than one backup PID to be assigned to each primary PID.) 
   The user chooses the desired redundancy structure and instructs the NMS as to which boards are primary boards and which boards are backup boards. For example, the NMS may assign LID  30  to line card  16   a —previously assigned PID  500  by the MCD—as a user defined primary card, and the NMS may assign LID  30  to line card  16   n —previously assigned PID  513  by the MCD—as a user defined back-up card (see row  106 ,  FIG. 14   b ). The NMS may also assign LID  40  to port  44   a —previously assigned PID  1500  by the MCD—as a primary port, and the NMS may assign LID  40  to port  68   a —previously assigned PID  1600  by the MCD—as a back-up port (see row  107 ,  FIG. 14   c ). 
   In a 1:1 redundant system, each backup line card backs-up only one other line card and the NMS assigns a unique primary PID and a unique backup PID to each LID (no LIDs share the same PIDs). In a 1:N redundant system, each backup line card backs-up at least two other line cards and the NMS assigns a different primary PID to each LID and the same backup PID to at least two LIDs. For example, if computer system  10  is a 1:N redundant system, then one line card, for example, line card  16   n,  serves as the hardware backup card for at least two other line cards, for example, line cards  16   a  and  16   b.  If the NMS assigns an LID of  31  to line card  16   b,  then in logical to physical card table  100  (see row  109 ,  FIG. 14   b ), the NMS associates LID  31  with primary PID  501  (line card  16   b ) and backup PID  513  (line card  16   n ). As a result, backup PID  513  (line card  16   n ) is associated with both LID  30  and  31 . 
   The logical to physical card table provides the user with maximum flexibility in choosing a redundancy structure. In the same computer system, the user may provide full redundancy (1:1), partial redundancy (1:N), no redundancy or a combination of these redundancy structures. For example, a network manager (user) may have certain customers that are willing to pay more to ensure their network availability, and the user may provide a backup line card for each of that customer&#39;s primary line cards (1:1). Other customers may be willing to pay for some redundancy but not full redundancy, and the user may provide one backup line card for all of that customer&#39;s primary line cards (1:N). Still other customers may not need any redundancy, and the user will not provide any backup line cards for that customer&#39;s primary line cards. For no redundancy, the NMS would leave the backup PID field in the logical to physical table blank. Each of these customers may be serviced by separate computer systems or the same computer system. Redundancy is discussed in more detail below. 
   The NMS and MCD use the same numbering space for LIDs, PIDs and other assigned numbers to ensure that the numbers are different (no collisions). 
   The configuration database, for example, a Polyhedra relational database, supports an “active query” feature. Through the active query feature, other software applications can be notified of changes to configuration database records in which they are interested. The NMS database establishes an active query for all configuration database records to insure it is updated with all changes. The master SRM establishes an active query with configuration database  42  for LPCT  100  and LPPT  101 . Consequently, when the NMS adds to or changes these tables, configuration database  42  sends a notification to the master SRM and includes the change. In this example, configuration database  42  notifies master SRM  36  that LID  30  has been assigned to PID  500  and  513  and LID  31  has been assigned to PID  501  and  513 . The master SRM then uses card table  47  to determine the physical location of boards associated with new or changed LIDs and then tells the corresponding slave SRM of its assigned LID(s). In the continuing example, master SRM reads CT  47  to learn that PID  500  is line card  16   a,  PID  501  is line card  16   b  and PID  513  is line card  16   n.  The master SRM then notifies slave SRM  37   b  on line card  16   a  that it has been assigned LID  30  and is a primary line card, SRM  37   c  on line card  16   b  that it has been assigned LID  31  and is a primary line card and SRM  37   o  on line card  16   n  that it has been assigned LIDs  30  and  31  and is a backup line card. All three slave SRMs  37   b,    37   c  and  37   o  then set up active queries with configuration database  42  to insure that they are notified of any software load records (SLRs) created for their LIDs. A similar process is followed for the LIDs assigned to each port. 
   The NMS informs the user of the hardware available in computer system  10 . This information may be provided as a text list, as a logical picture in a graphical user interface (GUI), or in a variety of other formats. The user then uses the GUI to tell the NMS (e.g., NMS client  850   a,    FIG. 2   a ) how they want the system configured. 
   The user will select which ports (e.g.,  44   a – 44   d,    46   a – 46   f,    68   a – 68   n ) the NMS should enable. There may be instances where some ports are not currently needed and, therefore, not enabled. The user also needs to provide the NMS with information about the type of network connection (e.g., connection  70   a – 70   d,    72   a – 72   f,    74   a – 74   n ). For example, the user may want all ports  44   a – 44   d  on line card  16   a  enabled to run ATM over SONET. The NMS may start one ATM application to control all four ports, or, for resiliency, the NMS may start one ATM application for each port. Alternatively, each port may be enabled to run a different protocol (e.g., MPLS, IP, Frame Relay). 
   In the example given above, the user must also indicate the type of SONET fiber they have connected to each port and what paths to expect. For example, the user may indicate that each port  44   a – 44   d  is connected to a SONET optical fiber carrying an OC-48 stream. A channelized OC-48 stream is capable of carrying forty-eight STS-1 paths, sixteen STS-3c paths, four STS-12c paths or a combination of STS-1, STS-3c and STS-12c paths. A clear channel OC-48c stream carries one concatenated STS-48 path. In the example, the user may indicate that the network connection to port  44   a  is a clear channel OC-48 SONET stream having one STS-48 path, the network connection to port  44   b  is a channelized OC-48 SONET stream having three STS-12c paths (i.e., the SONET fiber is not at full capacity—more paths may be added later), the network connection to port  44   c  is a channelized OC-48 SONET stream having two STS-3c paths (not at full capacity) and the network connection to port  44   d  is a channelized OC-48 SONET stream having three STS-12c paths (not at full capacity). In the current example, all paths within each stream carry data transmitted according to the ATM protocol. Alternatively, each path within a stream may carry data transmitted according to a different protocol. 
   The NMS (e.g., NMS server  851   a – 851   n ) uses the information received from the user (through the GUI/NMS client) to create records in several tables in the configuration database, which are then copied to the NMS database. These tables are accessed by other applications to configure computer system  10 . One table, the service endpoint table (SET)  76  (see also  FIG. 14   a ), is created when the NMS assigns a unique service endpoint number (SE) to each path on each enabled port and corresponds each service endpoint number with the physical identification number (PID) previously assigned to each port by the MCD. Through the use of the logical to physical port table (LPPT), the service endpoint number also corresponds to the logical identification number (LID) of the port. For example, since the user indicated that port  44   a  (PID  1500 ) has a single STS-48 path, the NMS assigns one service endpoint number (e.g. SE  1 , see row  78 ,  FIG. 14   a ). Similarly, the NMS assigns three service endpoint numbers (e.g., SE  2 ,  3 ,  4 , see rows  80 – 84 ) to port  44   b  (PID  1501 ), two service endpoint numbers (e.g., SE  5 ,  6 , see rows  86 ,  88 ) to port  44   c  (PID  1502 ) and three service endpoint numbers (e.g., SE  7 ,  8 ,  9 , see rows  90 ,  92 ,  94 ) to port  44   d.    
   Service endpoint managers (SEMs) within the modular system services of the kernel software running on each line card use the service endpoint numbers assigned by the NMS to enable ports and to link instances of applications, for example, ATM, running on the line cards with the correct port. The kernel may start one SEM to handle all ports on one line card, or, for resiliency, the kernel may start one SEM for each particular port. For example, SEMs  96   a – 96   d  are spawned to independently control ports  44   a – 44   d.    
   The service endpoint managers (SEMs) running on each board establish active queries with the configuration database for SET  76 . Thus, when the NMS changes or adds to the service endpoint table (SET), the configuration database sends the service endpoint manager associated with the port PID in the SET a change notification including information on the change that was made. In the continuing example, configuration database  42  notifies SEM  96   a  that SET  76  has been changed and that SE  1  was assigned to port  44   a  (PID  1500 ). Configuration database  42  notifies SEM  96   b  that SE  2 ,  3 , and  4  were assigned to port  44   b  (PID  1501 ), SEM  96   c  that SE  5  and  6  were assigned to port  44   c  (PID  1502 ) and SEM  96   d  that SE  7 ,  8 , and  9  were assigned to port  44   d  (PID  1503 ). When a service endpoint is assigned to a port, the SEM associated with that port passes the assigned SE number to the port driver for that port using the port PID number associated with the SE number. 
   To load instances of software applications on the correct boards, the NMS creates software load records (SLR)  128   a – 128   n  in configuration database  42 . The SLR includes the name  130  ( FIG. 14   f ) of a control shim executable file and an LID  132  for cards on which the application must be spawned. In the continuing example, NMS  60  creates SLR  128   a  including the executable name atm_cntrl.exe and card LID  30  (row  134 ). The configuration database detects LID  30  in SLR  128   a  and sends slave SRMs  37   b  (line card  16   a ) and  37   o  (line card  16   n ) a change notification including the name of the executable file (e.g., atm_cntrl.exe) to be loaded. The primary slave SRMs then download and execute a copy of atm_cntrl.exe  135  from memory  40  to spawn the ATM controllers (e.g., ATM controller  136  on line card  16   a ). Since slave SRM  37   o  is on backup line card  16   n,  it may or may not spawn an ATM controller in backup mode. Software backup is described in more detail below. Instead of downloading a copy of atm_cntrl.exe  135  from memory  40 , a slave SRM may download it from another line card that already downloaded a copy from memory  40 . There may be instances when downloading from a line card is quicker than downloading from central processor  12 . Through software load records and the tables in configuration database  42 , applications are downloaded and executed without the need for the system services, including the SRM, or any other software in the kernel to have information as to how the applications should be configured. The control shims (e.g., atm_cntrl.exe  135 ) interpret the next layer of the application (e.g., ATM) configuration. 
   For each application that needs to be spawned, for example, an ATM application and a SONET application, the NMS creates an application group table. Referring to  FIG. 14   d,  ATM group table  108  indicates that four instances of ATM (i.e., group number  1 ,  2 ,  3 ,  4 )—corresponding to four enabled ports  44   a – 44   n —are to be started on line card  16   a  (LID  30 ). If other instances of ATM are started on other line cards, they would also be listed in ATM group table  108  but associated with the appropriate line card LID. ATM group table  108  may also include additional information needed to execute ATM applications on each particular line card. (See description of software backup below.) 
   In the above example, one instance of ATM was started for each port on the line card. This provides resiliency and fault isolation should one instance of ATM fail or should one port suffer a failure. An even more resilient scheme would include multiple instances of ATM for each port. For example, one instance of ATM may be started for each path received by a port. 
   The application controllers on each board now need to know how many instances of the corresponding application they need to spawn. This information is in the application group table in the configuration database. Through the active query feature, the configuration database notifies the application controller of records associated with the board&#39;s LID from corresponding application group tables. In the continuing example, configuration database  42  sends ATM controller  136  records from ATM group table  108  that correspond to LID  30  (line card  16   a ). With these records, ATM controller  136  learns that there are four ATM groups associated with LID  30  meaning ATM must be instantiated four times on line card  16   a.  ATM controller  136  asks slave SRM  37   b  to download and execute four instances (ATM  110 – 113 ,  FIG. 15 ) of atm.exe  138 . 
   Once spawned, each instantiation of ATM  110 – 113  sends an active database query to search ATM interface table  114  for its corresponding group number and to retrieve associated records. The data in the records indicates how many ATM interfaces each instantiation of ATM needs to spawn. Alternatively, a master ATM application (not shown) running on central processor  12  may perform active queries of the configuration database and pass information to each slave ATM application running on the various line cards regarding the number of ATM interfaces each slave ATM application needs to spawn. 
   Referring to  FIGS. 14   e  and  15 , for each instance of ATM  110 – 113  there may be one or more ATM interfaces. To configure these ATM interfaces, the NMS creates an ATM interface table  114 . There may be one ATM interface  115 – 122  per path/service endpoint or multiple virtual ATM interfaces  123 – 125  per path. This flexibility is left up to the user and NMS, and the ATM interface table allows the NMS to communicate this configuration information to each instance of each application running on the different line cards. For example, ATM interface table  114  indicates that for ATM group  1 , service endpoint  1 , there are three virtual ATM interfaces (ATM-IF  1 – 3 ) and for ATM group  2 , there is one ATM interface for each service endpoint: ATM-IF  4  and SE  2 ; ATM-IF  5  and SE  3 ; and ATM-IF  6  and SE  4 . 
   Computer system  10  is now ready to operate as a network switch using line card  16   a  and ports  44   a – 44   d.  The user will likely provide the NMS with further instructions to configure more of computer system  10 . For example, instances of other software applications, such as an IP application, and additional instances of ATM may be spawned (as described above) on line cards  16   a  or other boards in computer system  10 . 
   As shown above, all application dependent data resides in memory  40  and not in kernel software. Consequently, changes may be made to applications and configuration data in memory  40  to allow hot (while computer system  10  is running) upgrades of software and hardware and configuration changes. Although the above described power-up and configuration of computer system  10  is complex, it provides massive flexibility as described in more detail below. 
   Template Driven Service Provisioning: 
   Instead of using the GUI to interactively provision services on one network device in real time, a user may provision services on one or more network devices in one or more networks controlled by one or more network management systems (NMSs) interactively and non-interactively using an Operations Support Services (OSS) client and templates. At the heart of any carrier&#39;s network is the OSS, which provides the overall network management infrastructure and the main user interface for network managers/administrators. The OSS is responsible for consolidating a diverse set of element/network management systems and third-party applications into a single system that is used, for example, to detect and resolve network faults (Fault Management), configure and upgrade the network (Configuration Management), account and bill for network usage (Accounting Management), oversee and tune network performance (Performance Management), and ensure ironclad network security (Security Management). FCAPS are the five functional areas of network management as defined by the International Organization for Standardization (ISO). Through templates one or more NMSs may be integrated with a telecommunication network carrier&#39;s OSS. 
   Templates are metadata and include scripts of instructions and parameters. In one embodiment, instructions within templates are written in ASCII text to be human readable. There are three general categories of templates, provisioning templates, control templates and batch templates. A user may interactively connect the OSS client with a particular NMS server and then cause the NMS server to connect to a particular device. Instead, the user may create a control template that non-interactively establishes these connections. Once the connections are established, whether interactively or non-interactively, provisioning templates may be used to complete particular provisioning tasks. The instructions within a provisioning template cause the OSS client to issue appropriate calls to the NMS server which cause the NMS server to complete the provisioning task, for example, by writing/modifying data within the network device&#39;s configuration database. Batch templates may be used to concatenate a series of templates and template modifications (i.e., one or more control and provisioning templates) to provision one or more network devices. Through the client/server based architecture, multiple OSS clients may work with one or more NMS servers. Database view ids and APIs for the OSS client may be generated using the logical model and code generation system ( FIG. 3   c ) to synchronize the integration interfaces between the OSS clients and the NMS servers. 
   Interactively, a network manager may have an OSS client execute many provisioning templates to complete many provisioning tasks. Instead, the network manager may order and sequence the execution of many provisioning templates within a batch template to non-interactively complete the many provisioning tasks and build custom services. In addition, execution commands followed by control template names may be included within batch templates to non-interactively cause an OSS client to establish connections with particular NMS servers and network devices. For example, a first control template may designate a network device to which the current OSS client and NMS server are not connected. Including an execution command followed by the first control template name in a batch template will cause the OSS client to issue calls to the NMS server to cause the NMS server to access the different network device. As another example, a second control template may designate an NMS server and a network device to which the OSS client is not currently connected. Including an execution command followed by the second control template name will cause the OSS client to set up connections to both the different NMS server and the different network device. Moreover, batch templates may include execution commands followed by provisioning template names after each execution command and control template to provision services within the network devices designated by the control templates. Through batch templates, therefore, multiple control templates and provisioning templates may be ordered and sequenced to provision services within multiple network devices in multiple networks controlled by multiple NMSs. 
   Calls issued by the OSS client to the NMS server may cause the NMS server to immediately provision services or delay provisioning services until a predetermined time, for example, a time when the network device is less likely to be busy. Templates may be written to apply to different types of network devices. 
   A “command line” interactive interpreter within the OSS client may be used by a network manager to select and modify existing templates or to create new templates. Templates may be generated for many various provisioning tasks, for example, setting up a permanent virtual circuit (PVC), a switched virtual circuit (SVC), a SONET path (SPATH), a traffic descriptor (TD) or a virtual ATM interface (VAIF). Once a template is created, a network manager change default parameters within the template to complete particular provisioning tasks. A network manager may also copy a template and modify it to create a new template. 
   Referring to  FIG. 3   i,  using the interactive interpreter, a network administrator may provision services by selecting (step  888 ) a template and using the default parameters within that template or copying and renaming (step  889 ) a particular provisioning template corresponding to a particular provisioning task and either accepting default parameter values provided by the template or changing (step  890 ) those default values to meet the administrator&#39;s needs. The network administrator may also change parameters and instructions within a copy of a template to create a new template. The modified provisioning templates are sent to or loaded into (step  891 ) the OSS client, which executes the instructions within the template and issues the appropriate calls (step  892 ) to the NMS server to satisfy the provisioning need. The OSS client may be written in JAVA and employ script technology. In response to calls received from the OSS client, the NMS server may execute (step  894 ) the provisioning requests defined by a template immediately or in a “batch-mode” (step  893 ), perhaps with other calls received from the OSS client or other clients, at a time when network transactions are typically low (e.g., late at night). 
   Referring to  FIGS. 3   j – 3   k , at the interactive interpreter prompt  912  (e.g., Enetcli&gt;) a network manager may type in “help” and be provided with a list (e.g., list  913 ) of commands that are available. In one embodiment, available commands may include bye, close, execute, help, load, manage, open, quit, showCurrent, showTemplate, set, status, writeCurrent, and writeTemplate. Many different commands are possible. The bye command allows the network manager to exit the interactive interpreter, the close command allows the network manager to close a connection between the OSS client and that NMS server, and the execute command followed by a template type causes the OSS client to execute the instructions within the loaded template corresponding to that template type. 
   As shown, the help command alone causes the interactive interpreter to display the list of commands. The help command followed by another command provides help information about that command. The load command followed by a template type and a named template loads the named template into the OSS client such that any commands followed by the template type will use the named/loaded template. The manage command followed by an IP address of a network device causes the OSS client to issue a call to an NMS server to establish a connection between the NMS server and that network device. Alternatively, a username and password may also need to be supplied. The open command followed by an NMS server IP address causes the OSS client to open a connection with that NMS server, and again, the network manager may also need to supply a username and password. Instead of an IP address, a domain name server (DNS) name may be provided and a host look up may be used to determine the IP address and access the corresponding device. 
   The showCurrent command followed by a template type will cause the interactive interpreter to display current parameter values for the loaded template corresponding to that template type. For example, showCurrent SPATH  914  displays a list  915  of parameters and current parameter values for the loaded template corresponding to the SPATH template type. The showTemplate command followed by a template type will cause the OSS client to display available parameters and acceptable parameter values for each parameter within the loaded template. For example, showTemplate SPATH  916  causes the interactive interpreter to display the available parameters  917  within the loaded template corresponding to the SPATH template type. The set command followed by a template type, a parameter name and a value will change the named parameter to the designated value within the loaded template, and a subsequent showCurrent command followed by that template type will show the new parameter value within the loaded. 
   The status command  918  will cause the interactive interpreter to display a status of the current interactive interpreter session. For example, the interactive interpreter may display the name  919  of an NMS server to which the OSS client is currently connected (as shown in  FIGS. 3   j – 3   k,  the OSS client is currently not connected to an NMS server) and the interactive interpreter may display the names  920  of available template types. The writeCurrent command followed by a template type and a new template name will cause the interactive interpreter to make a copy of the loaded template, including current parameter values, with the new template name. The writeTemplate command followed by a template type and a new template name, will cause the interactive interpreter to make a copy of the template with the new template name with placeholders values (i.e., &lt;String&gt;) that indicate the network manager needs to fill in the template with the required datatypes as parameter values. The network manager may then use the load command followed by the new template name to load the new template into the OSS client. 
   Referring to  FIG. 3   l,  from the interactive interpreter prompt (e.g., Enetcli&gt;), a network manager may interactively provision services on a network device. The network manager begins by typing an open command  921  a followed by the IP address of an NMS server to cause the OSS client to open a connection  921   b  with that NMS server. The network manager may then issue a manage command  921   c  followed by the IP address of a particular network device to cause the OSS client to issue a call  921   d  to the NMS server to cause the NMS server to open a connection  921   e  with that network device. 
   The network manager may now provision services within that network device by typing in an execute command  921   f  followed by a template type. For example, the network manager may type “execute SPATH” at the Enetcli&gt; prompt to cause the OSS client to execute the instructions  921   g  within the loaded SPATH template using the parameter values within the loaded SPATH template. Executing the instructions causes the OSS client to issue calls to the NMS server, and these calls cause the NMS server to complete the provisioning task  921   h.  For example, following an execute SPATH command, the NMS server will set up a SONET path in the network device using the parameter values passed to the NMS server by the OSS client from the template. 
   At any time from the Enetcli&gt; prompt, a network manager may change the parameter values within a template. Again, the network manager may use showCurrent followed by a template type to see the current parameter values within the loaded template or showTemplate to see the available parameters within the loaded template. The network manager may then use the set command followed by the template type, parameter name and new parameter value to change a parameter value within the loaded template. For example, after the network manager sets up a SONET path within the network device, the network manager may change one or more parameter values within the loaded SPATH template and re-execute the SPATH template to set up a different SONET path within the same network device. 
   Once a connection to a network device is open, the network manager may interactively execute any template any number of times to provision services within that network device. The network manager may also create new templates and execute those. The network manager may simply write a new template or use the writeCurrent or writeTemplate commands to copy an existing template into a new template name and then edit the instructions within the new template. 
   After provisioning services within a first network device, the network manager may open a connection with a second network device to provision services within that second network device. If the NMS server currently connected to the OSS client is capable of establishing a connection with the second network device, then the network manager may simply open a connection to the second network device. If the NMS server currently connected to the OSS client is not capable of establishing a connection with the second network device, then the network manager closes the connections with the NMS server and then opens connections with a second NMS server and the second network device. Thus, a network manager may easily manage/provision services within multiple network devices within multiple networks even if they are managed by different NMS servers. In addition, other network managers may provision services on the same network devices through the same NMS servers using other OSS clients that are perhaps running on other computer systems. That is, multiple OSS clients may be connected to multiple NMS servers. 
   Instead of interactively establishing connections with NMS servers and network devices, control templates may be used to non-interactively establish these connections. Referring to  FIG. 3   m,  using a showCurrent command  922  followed by CONTROL causes the interactive interpreter to display parameters available in the loaded CONTROL template. 
   In one embodiment, an execute control command will automatically cause the OSS client to execute instructions within the loaded CONTROL template and open a connection to an NMS server designated within the CONTROL template. Since the OSS client automatically opens a connection with the designated NMS server, the open command may but need not be included within the CONTROL template. In this example, the CONTROL template includes “localhost”  923   a  as the DNS name of the NMS server with which the OSS client should open a connection. In one embodiment, “localhost” refers to the same system as the OSS client. A username  923   b  and password  923   c  may also need to be used to open the connection with the localhost NMS server. The CONTROL template also includes the manage command  923   d  and a network device IP address  923   e  of 192.168.9.202. With this information (and perhaps the username and password or another username and password), the OSS client issues calls to the localhost NMS server to cause the server to set up a connection with that network device. 
   The template may also include an output file name  923   f  where any output/status information generated in response to the execution of the CONTROL template will be sent. The template may also include a version number  923   g.  Version numbers allow a new template to be created with the same name as an old template but with a new version number, and the new template may include additional/different parameters and/or instructions. Using version numbers, both old (e.g., not upgraded) and new OSS clients may use the templates but only access those templates having particular version numbers that correspond to the functionality of each OSS client. 
   Once connections with an NMS server and network device are established (either interactively or non-interactively through a control template), services within the network device may be provisioned. As described above, a network manager may interactively provision services by issuing execute commands followed by provisioning template types. Alternatively, a network manager may provision services non-interactively through batch templates, which include an ordered list of tasks, including execute commands followed by provisioning template types. 
   Referring to  FIG. 3   n,  a batch template type named BATCH  924  includes an ordered list of tasks, including execute commands followed by provisioning template types. When a network manager issues an execute command followed by the BATCH template type at the Enetcli&gt; prompt, the OSS client will carry out each of the tasks within the loaded BATCH template. In this example, task 1   924   a  includes “execute SPATH” which causes the OSS client to establish a SONET path within the network device to which a connection is open, task 2   924   b  includes “execute PVC” to cause the OSS client to set up a permanent virtual circuit within the network device, and task 3   924   c  includes “execute SPVC” to cause the OSS client to set up a soft permanent virtual circuit within the network device. 
   If multiple similar provisioning tasks are needed, then the network manager may use writeCurrent or writeTemplate to create multiple similar templates (i.e., same template type with different template names), change or add parameter values within these multiple similar templates using the set command, and sequentially load and execute each of the different named templates. For example, SPVC is the template type and task 3  causes the OSS to execute instructions within the previously loaded named template. Spvc 1  and spvc 2  are two different named templates (or template instantiations) corresponding to the SPVC template type for setting up soft permanent virtual circuits having different parameters from each other and the loaded template to set up different SPVCs. In this example, the BATCH template then includes task 4   924   d  including “load SPVC spvc 1 ” to load the spvc 1  template and then task 5   924   e  “execute SPVC” to cause the OSS client to execute the loaded spvc 1  template and set up a different SPVC. Similarly, task 6   924   f  includes “load SPVC spvc 2 ” and task 7   924   e  includes “execute SPVC” to cause the OSS client to execute the loaded spvc 2  template and set up yet another different SPVC. 
   Alternatively, the batch template may include commands for altering an existing template such that multiple similar templates are not necessary. For example, the loaded BATCH template may include task 50   924   g  “set SPATH PortID  3 ” to cause the OSS client to change the PortID parameter within the SPATH template to 3. The BATCH template then includes task 51   924   h  “execute SPATH”  924   g  to cause the OSS client to execute the SPATH template including the new parameter value which sets up a different SONET path. A BATCH template may include many set commands to change parameter values followed by execute commands to provision multiple similar services within the same network device. For example, the BATCH template may further include task 52   924   i  “set SPATH SlotID  2 ” followed by task 53   924   j  “execute SPATH” to set up yet another different SONET path. Using this combination of set and execute commands eliminates the need to write, store and keep track of multiple similar templates. 
   Batch templates may also be used to non-interactively provision services within multiple different network devices by ordering and sequencing tasks including execute commands followed by control template types and then execute commands followed by provisioning template types. Referring to  FIG. 3   o,  instead of non-interactively establishing connections with an NMS server and a network device using a control template, a batch template may be used. For example, the first task in a loaded BATCH template  925  may be task 1   925   a  “execute CONTROL”. This will cause the OSS client to execute the loaded CONTROL template to establish connections with the NMS server and the network device designated within the loaded CONTROL template (e.g., localhost and 192.168.9.202). The BATCH template then includes provisioning tasks, for example, task 2   925   b  includes “execute SPATH” to set up a SONET path, and task 3   925   c  includes “set SPATH PortID  3 ” and task 4   925   d  includes “execute SPATH” to set up a different SONET path. Many additional provisioning tasks for this network device may be completed in this way. 
   The BATCH template may then have a task including a set command to modify one or more parameters within a control template to cause the OSS client to set up a connection with a different network device and perhaps a different NMS server. Where the network manager wishes to provision a network device capable of being connected to through the currently connected NMS server, for example, localhost, then the BATCH template need only have task 61   925   e  including “set CONTROL System” followed by the IP address of the different network device, for example, 192.168.9.201. The BATCH template then has a task  62   925   f  including “execute CONTROL”, which causes the OSS client to issue calls to the localhost NMS server to establish a connection with the different network device. The BATCH template may then have tasks including execute commands followed by provisioning templates, for example, task  63   925   g  including “execute SPATH”, to provision services within the different network device. 
   If the network manager wishes to provision a network device coupled with another NMS server, then the BATCH template includes, for example, task  108   925   h  including “close” to drop the connection between the OSS client and localhost NMS server. The BATCH template may then have, for example, task  109   925   i  including “set CONTROL Server Server 1 ” to change the server parameter within the loaded CONTROL template to Server 1  and task  110   925   j  including “set CONTROL System 192.168.8.200” to change the network device parameter within the loaded CONTROL template to the IP address of the new network device. The BATCH template may then have task  111   925   k  including “execute CONTROL” to cause the OSS client to set up connections to the Server 1  NMS server and to network device 192.168.8.200. The BATCH template may then include tasks with execute commands followed by provisioning template types to provision services within the network device, for example, task  112   925 L includes “execute SPATH”. 
   The templates and interactive interpreter/OSS client may be loaded and executed on a central OSS computer system(s) and used to provision services in one or more network devices in one or more network domains. A network administrator may install an OSS client at various locations and/or for “manage anywhere” purposes, web technology may be used to allow a network manager to download an OSS client program from a web accessible server onto a computer at any location. The network manager may then use the OSS client in the same manner as when it is loaded onto a central OSS computer system. Thus, the network manager may provision services from any computer at any location. 
   Provisioning templates may be written to apply to different types of network devices. The network administrator does not need to know details of the network device being provisioned as the parameters required and available for modification are listed in the various templates. Consequently, the templates allow for multifaceted integration of different network management systems (NMS) into existing OSS infrastructures. 
   Instead of using template executable files and an OSS client, network managers may prefer to use their standard OSS interface to provision services in various network devices. In one embodiment, therefore, a single OSS client application programming interface (API) and a library of compiled code may be linked directly into the OSS software. The library of compiled code is a subset of the compiled code used to create the OSS client, with built-in templates including provisioning, control, batch and other types of templates. The OSS software then uses the supported templates as documentation of the necessary parameters needed for each provisioning task and presents template streams (null terminated arrays of arguments that serialize the totality of arguments required to construct a supported template) via the single API for potential alteration through the OSS standard interface. Since the network managers are comfortable working with the OSS interface, provisioning services may be made more efficient and simple by directly linking the OSS client API and templates into the OSS software. 
   Typically, OSS software is written in C or C++ programming language. In one embodiment, the OSS client and templates are written in JAVA, and JAVA Native Interface (JNI) is used by the OSS software to access the JAVA OSS client API and templates. 
   Inter-Process Communication: 
   As described above, the operating system assigns a unique process identification number (proc_id) to each spawned process. Each process has a name, and each process knows the names of other processes with which it needs to communicate. The operating system keeps a list of process names and the assigned process identification numbers. Processes send messages to other processes using the assigned process identification numbers without regard to what board is executing each process (i.e., process location). Application Programming Interfaces (APIs) define the format and type of information included in the messages. 
   The modular software architecture configuration model requires a single software process to support multiple configurable objects. For example, as described above, an ATM application may support configurations requiring multiple ATM interfaces and thousands of permanent virtual connections per ATM interface. The number of processes and configurable objects in a modular software architecture can quickly grow especially in a distributed processing system. If the operating system assigns a new process for each configurable object, the operating system&#39;s capabilities may be quickly exceeded. For example, the operating system may be unable to assign a process for each ATM interface, each service endpoint, each permanent virtual circuit, etc. In some instances, the process identification numbering scheme itself may not be large enough. Where protected memory is supported, the system may have insufficient memory to assign each process and configurable object a separate memory block. In addition, supporting a large number of independent processes may reduce the operating system&#39;s efficiency and slow the operation of the entire computer system. 
   One alternative is to assign a unique process identification number to only certain high level processes. Referring to  FIG. 16   a,  for example, process identification numbers may only be assigned to each ATM process (e.g., ATMs  240 ,  241 ) and not to each ATM interface (e.g., ATM IFs  242 – 247 ) and process identification numbers may only be assigned to each port device driver (e.g., device drivers  248 ,  250 ,  252 ) and not to each service endpoint (e.g., SE  253 – 261 ). A disadvantage to this approach is that objects within one high level process will likely need to communicate with objects within other high level processes. For example, ATM interface  242  within ATM  240  may need to communicate with SE  253  within device driver  248 . ATM IF  242  needs to know if SE  253  is active and perhaps certain other information about SE  253 . Since SE  253  was not assigned a process identification number, however, neither ATM  240  nor ATM IF  242  knows if it exists. Similarly, ATM IF  242  knows it needs to communicate with SE  253  but does not know that device driver  248  controls SE  253 . 
   One possible solution is to hard code the name of device driver  248  into ATM  240 . ATM  240  then knows it must communicate with device driver  248  to learn about the existence of any service endpoints within device driver  248  that may be needed by ATM IF  242 ,  243  or  244 . Unfortunately, this can lead to scalability issues. For instance, each instantiation of ATM (e.g., ATM  240 ,  241 ) needs to know the name of all device drivers (e.g., device drivers  248 ,  250 ,  252 ) and must query each device driver to locate each needed service endpoint. An ATM query to a device driver that does not include a necessary service endpoint is a waste of time and resources. In addition, each high level process must periodically poll other high level processes to determine whether objects within them are still active (i.e., not terminated) and whether new objects have been started. If the object status has not changed between polls, then the poll wasted resources. If the status did change, then communications have been stalled for the length of time between polls. In addition, if a new device driver is added (e.g., device driver  262 ), then ATM  240  and  241  cannot communicate with it or any of the service endpoints within it until they have been upgraded to include the new device driver&#39;s name. 
   Preferably, computer system  10  implements a name server process and a flexible naming procedure. The name server process allows high level processes to register information about the objects within them and to subscribe for information about the objects with which they need to communicate. The flexible naming procedure is used instead of hard coding names in processes. Each process, for example, applications and device drivers, use tables in the configuration database to derive the names of other configurable objects with which they need to communicate. For example, both an ATM application and a device driver process may use an assigned service endpoint number from the service endpoint table (SET) to derive the name of the service endpoint that is registered by the device driver and subscribed for by the ATM application. Since the service endpoint numbers are assigned by the NMS during configuration, stored in SET  76  and passed to local SEMs, they will not be changed if device drivers or applications are upgraded or restarted. 
   Referring to  FIG. 16   b,  for example, when device drivers  248 ,  250  and  252  are started they each register with name server (NS)  264 . Each device driver provides a name, a process identification number and the name of each of its service endpoints. Each device driver also updates the name server as service endpoints are started, terminated or restarted. Similarly, each instantiation of ATM  240 ,  241  subscribes with name server  264  and provides its name, process identification number and the name of each of the service endpoints in which it is interested. The name server then notifies ATM  240  and  241  as to the process identification of the device driver with which they should communicate to reach a desired service endpoint. The name server updates ATM  240  and  241  in accordance with updates from the device drivers. As a result, updates are provided only when necessary (i.e., no wasted resources), and the computer system is highly scalable. For example, if a new device driver  262  is started, it simply registers with name server  264 , and name server  264  notifies either ATM  240  or  241  if a service endpoint in which they are interested is within the new device driver. The same is true if a new instantiation of ATM—perhaps an upgraded version—is started or if either an ATM application or a device driver fails and is restarted. 
   Referring to  FIG. 16   c,  when the SEM, for example, SEM  96   a,  notifies a device driver, for example, device driver (DD)  222 , of its assigned SE number, DD  222  uses the SE number to generate a device driver name. In the continuing example from above, where the ATM over SONET protocol is to be delivered to port  44   a  and DD  222 , the device driver name may be for example, atm.se 1 . DD  222  publishes this name to NS  220   b  along with the process identification assigned by the operating system and the name of its service endpoints. 
   Applications, for example, ATM  224 , also use SE numbers to generate the names of device drivers with which they need to communicate and subscribe to NS  220   b  for those device driver names, for example, atm.se 1 . If the device driver has published its name and process identification with NS  220   b,  then NS  220   b  notifies ATM  224  of the process identification number associated with atm.se 1  and the name of its service endpoints. ATM  224  can then use the process identification to communicate with DD  222  and, hence, any objects within DD  222 . If device driver  222  is restarted or upgraded, SEM  96   a  will again notify DD  222  that its associated service endpoint is SE  1  which will cause DD  222  to generate the same name of atm.se 1 . DD  222  will then re-publish with NS  220   b  and include the newly assigned process identification number. NS  220   b  will provide the new process identification number to ATM  224  to allow the processes to continue to communicate. Similarly, if ATM  224  is restarted or upgraded, it will use the service endpoint numbers from ATM interface table  114  and, as a result, derive the same name of atm.se 1  for DD  222 . ATM  224  will then re-subscribe with NS  220   b.    
   Computer system  10  includes a distributed name server (NS) application including a name server process  220   a – 220   n  on each board (central processor and line card). Each name server process handles the registration and subscription for the processes on its corresponding board. For distributed applications, after each application (e.g., ATM  224   a – 224   n ) registers with its local name server (e.g.,  220   b – 220   n ), the name server registers the application with each of the other name servers. In this way, only distributed applications are registered/subscribed system wide which avoids wasting system resources by registering local processes system wide. 
   The operating system, through the use of assigned process identification numbers, allows for inter-process communication (IPC) regardless of the location of the processes within the computer system. The flexible naming process allows applications to use data in the configuration database to determine the names of other applications and configurable objects, thus, alleviating the need for hard coded process names. The name server notifies individual processes of the existence of the processes and objects with which they need to communicate and the process identification numbers needed for that communication. The termination, re-start or upgrade of an object or process is, therefore, transparent to other processes, with the exception of being notified of new process identification numbers. For example, due to a configuration change initiated by the user of the computer system, service endpoint  253  ( FIG. 16   b ), may be terminated within device driver  248  and started instead within device driver  250 . This movement of the location of object  253  is transparent to both ATM  240  and  241 . Name server  264  simply notifies whichever processes have subscribed for SE  253  of the newly assigned process identification number corresponding to device driver  250 . 
   The name server or a separate binding object manager (BOM) process may allow processes and configurable objects to pass additional information adding further flexibility to inter-process communications. For example, flexibility may be added to the application programming interfaces (APIs) used between processes. As discussed above, once a process is given a process identification number by the name server corresponding to an object with which it needs to communicate, the process can then send messages to the other process in accordance with a predefined application programming interface (API). Instead of having a predefined API, the API could have variables defined by data passed through the name server or BOM, and instead of having a single API, multiple APIs may be available and the selection of the API may be dependent upon information passed by the name server or BOM to the subscribed application. 
   Referring to  FIG. 16   d,  a typical API will have a predefined message format  270  including, for example, a message type  272  and a value  274  of a fixed number of bits (e.g., 32). Processes that use this API must use the predefined message format. If a process is upgraded, it will be forced to use the same message format or change the API/message format which would require that all processes that use this API also be similarly upgraded to use the new API. Instead, the message format can be made more flexible by passing information through the name server or BOM. For example, instead of having the value field  274  be a fixed number of bits, when an application registers a name and process identification number it may also register the number of bits it plans on using for the value field (or any other field). Perhaps a zero indicates a value field of 32 bits and a one indicates a value filed of 64 bits. Thus, both processes know the message format but some flexibility has been added. 
   In addition to adding flexibility to the size of fields in a message format, flexibility may be added to the overall message format including the type of fields included in the message. When a process registers its name and process identification number, it may also register a version number indicating which API version should be used by other processes wishing to communicate with it. For example, device driver  250  ( FIG. 16   b ) may register SE  258  with NS  264  and provide the name of SE  258 , device driver  250 &#39;s process identification number and a version number one, and device driver  252  may register SE  261  with NS  264  and provide the name of SE  261 , device driver  252 &#39;s process identification number and a version number (e.g., version number two). If ATM  240  has subscribed for either SE  258  or SE  261 , then NS  264  notifies ATM  240  that SE  258  and SE  261  exist and provides the process identification numbers and version numbers. The version number tells ATM  240  what message format and information SE  258  and SE  261  expect. The different message formats for each version may be hard coded into ATM  240  or ATM  240  may access system memory or the configuration database for the message formats corresponding to service endpoint version one and version two. As a result, the same application may communicate with different versions of the same configurable object using a different API. 
   This also allows an application, for example, ATM, to be upgraded to support new configurable objects, for example, new ATM interfaces, while still being backward compatible by supporting older configurable objects, for example, old ATM interfaces. Backward compatibility has been provided in the past through revision numbers, however, initial communication between processes involved polling to determine version numbers and where multiple applications need to communicate, each would need to poll the other. The name server/BOM eliminates the need for polling. 
   As described above, the name server notifies subscriber applications each time a subscribed for process is terminated. Instead, the name server/BOM may not send such a notification unless the System Resiliency Manager (SRM) tells the name server/BOM to send such a notification. For example, depending upon the fault policy/resiliency of the system, a particular software fault may simply require that a process be restarted. In such a situation, the name server/BOM may not notify subscriber applications of the termination of the failed process and instead simply notify the subscriber applications of the newly assigned process identification number after the failed process has been restarted. Data that is sent by the subscriber processes after the termination of the failed process and prior to the notification of the new process identification number may be lost but the recovery of this data (if any) may be less problematic than notifying the subscriber processes of the failure and having them hold all transmissions. For other faults, or after a particular software fault occurs a predetermined number of times, the SRM may then require the name server/BOM to notify all subscriber processes of the termination of the failed process. Alternatively, if a terminated process does not re-register within a predetermined amount of time, the name server/BOM may then notify all subscriber processes of the termination of the failed process. 
   Configuration Change: 
   Over time the user will likely make hardware changes to the computer system that require configuration changes. For example, the user may plug a fiber or cable (i.e., network connection) into an as yet unused port, in which case, the port must be enabled and, if not already enabled, then the port&#39;s line card must also be enabled. As other examples, the user may add another path to an already enabled port that was not fully utilized, and the user may add another line card to the computer system. Many types of configuration changes are possible, and the modular software architecture allows them to be made while the computer system is running (hot changes). Configuration changes may be automatically copied to persistent storage as they are made so that if the computer system is shut down and rebooted, the memory and configuration database will reflect the last known state of the hardware. 
   To make a configuration change, the user informs the NMS (e.g., NMS client  850   a,    FIG. 2   a ) of the particular change, and similar to the process for initial configuration, the NMS (e.g., NMS server  851   a,    FIG. 2   a ) changes the appropriate tables in the configuration database (copied to the NMS database) to implement the change. 
   Referring to  FIG. 17 , in one example of a configuration change, the user notifies the NMS that an additional path will be carried by SONET fiber  70   c  connected to port  44   c.  A new service endpoint (SE)  164  and a new ATM interface  166  are needed to handle the new path. The NMS adds a new record (row  168 ,  FIG. 14   a ) to service endpoint table (SET)  76  to include service endpoint  10  corresponding to port physical identification number (PID)  1502  (port  44   c ). The NMS also adds a new record (row  170 ,  FIG. 14   e ) to ATM instance table  114  to include ATM interface (IF)  12  corresponding to ATM group  3  and SE  10 . Configuration database  42  may automatically copy the changes made to SET  76  and ATM instance table  114  to persistent storage  21  such that if the computer system is shut down and rebooted, the changes to the configuration database will be maintained. 
   Configuration database  42  also notifies (through the active query process) SEM  96   c  that a new service endpoint (SE  10 ) was added to the SET corresponding to its port (PID  1502 ), and configuration database  42  also notifies ATM instantiation  112  that a new ATM interface (ATM-IF  166 ) was added to the ATM interface table corresponding to ATM group  3 . ATM  112  establishes ATM interface  166  and SEM  96   c  notifies port driver  142  that it has been assigned SE 10 . A communication link is established through NS  220   b.  Device driver  142  generates a service endpoint name using the assigned SE number and publishes this name and its process identification number with NS  220   b.  ATM interface  166  generates the same service endpoint name and subscribes to NS  220   b  for that service endpoint name. NS  220   b  provides ATM interface  166  with the process identification assigned to DD  142  allowing ATM interface  166  to communicate with device driver  142 . 
   Certain board changes to computer system  10  are also configuration changes. After power-up and configuration, a user may plug another board into an empty computer system slot or remove an enabled board and replace it with a different board. In the case where applications and drivers for a line card added to computer system  10  are already loaded, the configuration change is similar to initial configuration. The additional line card may be identical to an already enabled line card, for example, line card  16   a  or if the additional line card requires different drivers (for different components) or different applications (e.g., IP), the different drivers and applications are already loaded because computer system  10  expects such cards to be inserted. 
   Referring to  FIG. 18 , while computer system  10  is running, when another line card  168  is inserted, master MCD  38  detects the insertion and communicates with a diagnostic program  170  being executed by the line card&#39;s processor  172  to learn the card&#39;s type and version number. MCD  38  uses the information it retrieves to update card table  47  and port table  49 . MCD  38  then searches physical module description (PMD) file  48  in memory  40  for a record that matches the retrieved card type and version number and retrieves the name of the mission kernel image executable file (MKI.exe) that needs to be loaded on line card  168 . Once determined, master MCD  38  passes the name of the MKI executable file to master SRM 36. SRM  36  downloads MKI executable file  174  from persistent storage  21  and passes it to a slave SRM  176  running on line card  168 . The slave SRM executes the received MKI executable file. 
   Referring to  FIG. 19 , slave MCD  178  then searches PMD file  48  in memory  40  on central processor  12  for a match with its line card&#39;s type and version number to find the names of all the device driver executable files needed by its line card. Slave MCD  178  provides these names to slave SRM  176  which then downloads and executes the device driver executable files (DD.exe)  180  from memory  40 . 
   When master MCD  38  updates card table  47 , configuration database  42  updated NMS database  61  which sends NMS  60  (e.g., NMS Server  851   a,    FIG. 2   a ) a notification of the change including card type and version number, the slot number into which the card was inserted and the physical identification (PID) assigned to the card by the master MCD. The NMS is updated, assigns an LID and updates the logical to physical table and notifies the user of the new hardware. The user then tells the NMS how to configure the new hardware, and the NMS implements the configuration change as described above for initial configuration. 
   Logical Model Change: 
   Where software components, including applications, device drivers, modular system services, new mission kernel images (MKIs) and diagnostic software, for a new hardware module (e.g., a line card) are not already loaded and/or if changes or upgrades (hereinafter “upgrades”) to already loaded software components are needed, logical model  280  ( FIGS. 3   a – 3   c ) must be changed and new view ids and APIs, NMS JAVA interface files, persistent layer metadata files and new DDL files may need to be re-generated. Software model  286  is changed to include models of the new or upgraded software, and hardware model  284  is changed to include models of any new hardware. New logical model  280 ′ is then used by code generation system  336  to re-generate view ids and APIs for any changed software components, including any new applications, for example, ATM version two  360 , or device drivers, for example, device driver  362 , and, where necessary, to re-generate DDL files  344 ′ and  348 ′ including new SQL commands and data relevant to the new hardware and/or software. The new logical model is also used to generate, where necessary, new NMS JAVA interface files  347 ′ and new persistent layer metadata files  349 ′. 
   Each executable software component is then built. As described above with reference to  FIG. 3   e,  the build process involves compiling one or more source code files for the software component and then linking the resulting object code with the object code of associated libraries, a view id, an API, etc. to form an executable file. Each of the executable files and data files, for example, persistent layer metadata files and DDL files, are then provided to Kit Builder ( 861 ,  FIG. 3   f ), which combines the components into a Network Device Installation Kit. As previously mentioned, the Kit Builder may compress each of the software components to save space. Each Installation Kit is assigned a Global release version number to distinguish between different Installation Kits. 
   The Kit Builder also creates a packaging list  1200  ( FIG. 20   a ) and includes this in the Installation Kit. The packaging list includes a list of the software components in the Installation Kit and a list of “signatures”  1200   a – 1200   n  associated with the software components. 
   Software Component Signatures: 
   To facilitate upgrades of software components while the network device (e.g.,  10 ,  FIG. 1 ;  540 ,  FIGS. 35   a – 35   b ) is running (hot upgrades), a “signature” is generated for each software component. After installation (described below) within the network device of a new Installation Kit, only those software components whose signatures do not match the signatures of corresponding and currently executing software components will be upgraded. For example, different signatures associated with two ATM components represent different versions of those two ATM components. 
   Currently, software programmers assign a different version number to a software component when they change a software component. Since, the versioning process is controlled by or requires human intervention, this process is error prone. For example, if a changed software component is not assigned a new version number, then it may not be upgraded with other changed applications. If one or more of the upgraded applications work with the application that was not upgraded, errors and potentially a network device crash may occur. To avoid versioning errors, instead of assigning a version number, a signature is “machine generated” based on the content of the software component. 
   A simple program such as a checksum or cyclic redundancy checking (CRC) program may be used to generate the signature. The concern with such a simple program is that it may generate the same signature for a current software component and an upgrade of that component if the upgrade changes are not significant. Instead, a more robust program, such as a strong cryptographic program, may be used to generate the signatures for each software component. In one embodiment, the signatures are generated using the “Sha-1” cryptography utility (often called the “sha1sum”). Information regarding Sha-1, which is herein incorporated by reference, and a copy of Sha-1 may be located by citizens or permanent residents of the United States and Canada from the North American Cryptography Archives at www.cryptography.org. This web site also points to various other web sites for access to cryptographic programs available outside the United States and Canada. 
   The Sha-1 utility is a secure hash algorithm that uses the contents of a software component to generate a signature that is 20 bytes in length. The Sha-1 utility is robust enough to detect even small changes to a software component and, thus, generate a different signature. Due to the sensitivity of the Sha-1 utility, the signature may also be referred to as a “finger print” or a “digest”. Using the Sha-1 utility or another signature generating program, eliminates the errors often caused when humans generate version numbers. 
   Other signature generating programs may also be used. For example, hash functions such as MD2, MD4, MD5 or Ripemd128 or Ripemd160 may be used or a keyed hash function, such as HMAC, may be used with any of these hash functions. MD5 will produce a 128-bit “fingerprint” or “message digest” for each software component. Information regarding MD5, which is herein incorporated by reference, may be gotten from the following web site: http://userpages.umbc.edu/˜mabzugl/cs/md5/md5.html. Ripemd128 produces a 16 byte digest and Ripemd169 produces a 20 byte digest. Information regarding Ripemd128 or Ripemd160, which is herein incorporated by reference, may be found at the following web site: http://www.esat.kuleuven.ac.be/˜bosselae/ripemd160.html#What . 
   Referring to  FIG. 20   b,  once a software component  1202  is built, it is passed to the signature generating program  1204 , for example, the Sha-1 utility. The number generated by the signature generating program is the signature  1206  for that software component and it is appended to the built software component  1208 . These steps are repeated for each software component added to the packaging list, and as Kit Builder  861  ( FIG. 3   f ) adds each software component to the packaging list, it retrieves the signature appended to each software component and inserts it in the packaging list corresponding to the appropriate software component. 
   Often build programs, including the compiler and the linker, insert a date and time or other extraneous data in a built software component. In addition, other “profile” type data may also be appended to each software component such as the name of the user who executed the build, the Global version number for the new release, the configuration specification used for the build and various other data. Such extraneous data may cause the signature generating program to generate different signatures for a software component built at one time and then re-built at another time even if the software component itself has not been changed. To avoid this, the signature generating program may be given the built software component with the extraneous data stripped out or with the extraneous data blocked out such that the signature generating program will not consider it when generating the signature. 
   Certain software components are not built, such as meta data files, for example, PMD file  48  ( FIG. 12   a ). These software components are also passed to the signature generating program, and the generated signature is appended to the file. Similar to the built software components, the Kit Builder adds these software components to the packaging list, retrieves the signature appended to each software component and inserts it in the packaging list corresponding to the appropriate software component. 
   The signatures within the packaging list are used after installation of the new Installation Kit within the network device to determine which software components need to be upgraded. Since each new Installation Kit may include all software components required by the network device, including unchanged and changed software components, a hot upgrade is only practical if the changed software components may be easily and accurately identified. For example, an Installation Kit may include a large number of software components, such as 50–60 load modules, 2–3 kernels and 10–15 meta data files. If changed software components cannot be identified, then the network device will need to be rebooted in order to implement all the software components in the new Installation Kit. Signatures allow for a quick and accurate determination as to which components changed and, thus, need to be upgraded. 
   Installation: 
   A customer/user may receive a new Installation Kit on a CD, or the customer/user may be given access to a web site where the new Installation Kit may be accessed. Whether a CD is loaded into a CD player  1209  ( FIG. 20   c ) or a web site is accessed, an Install icon  1210  will be displayed on the screen of the user&#39;s computer  1212 . Computer  1212  may be the same computer (e.g., 62) that is running the NMS or a different computer. To initiate installation, the user double clicks their mouse on the Install icon to cause, for example, a JAVA application  1216  ( FIG. 20   d ), to perform the installation. 
   Initially, the JAVA application causes a dialog box  1214  to appear to welcome the user and ask for an internet (IP) address  1213   a  of the network device into which the new Installation Kit is to be installed. For security, the dialog box may also request a username  1213   b  and a password  1213   c.  After verifying the username and password with the network device, the JAVA application uses the supplied IP address to download the new Installation Kit, for example, release 1.1  1218 , including the packaging list, to a new sub-directory  1220  within an installation directory  1222  in configuration database  42 . Any previously loaded Installation Kits, which have not been deleted, may be found in different sub-directories, for example, release 1.0 may be loaded in sub-directory  1224 . 
   In addition, if the configuration database schema (i.e., meta data/data structure) needs to be changed, the JAVA application also causes a dialog box  1215  ( FIG. 20   e ) to appear. Dialog box  1215  prompts the user for an NMS database system ID  1215   a,  a database port address  1215   b  and a database password  1215   c.  The JAVA application then uploads the existing meta data (used by the NMS) and user data  1221   a  from the network device&#39;s configuration database into a work area  1254  within the NMS database  61 . The JAVA application then performs the conversion in accordance with the new meta data provided in the new release and then downloads a DDL script  1221   b  into new sub-directory  1220  within the network device. 
   The network device may then be rebooted (cold upgrade), in which case, once rebooted the network device will use all the software components, including the DDL script for the converted configuration database, of release 1.1 in sub-directory  1220 . Instead, the DDL script for the converted configuration database may reside in sub-directory  1220  until the user elects to make the upgrade, as described below. 
   Upgrade: 
   Upgrades are managed by a software management system (SMS) service. Upgrades may be implemented while the network device is running (hot upgrades), or upgrades may be implemented by re-booting the network device (cold upgrades). Hot upgrades are preferred to limit any disruption in service provided by the network device. In addition, certain upgrades may only affect certain services, and a hot upgrade may be implemented such that the unaffected services experience no disruption while the affected services experience only minimal disruption. The SMS is one of the modular system services, and like the MCD and the SRM, the SMS is a distributed application. Referring to  FIG. 21   a,  a master SMS  184  is executed by central processor  12  while slave SMSs  186   a – 186   n  are executed on each board (e.g.,  12  and  16   a – 16   n ). 
   Master SMS  184  periodically polls installation directory  1222  for new sub-directories including new releases, for example, release 1.1  1218  in sub-directory  1220 . When the master SMS detects a new release, it opens (and decompresses, if necessary) the packaging list in the new sub-directory and verifies that each software component listed in the packaging list is also stored in the new sub-directory. The master SMS then performs a checksum on each software component and compares the generated checksum to the checksum appended to the software component. 
   Once all software components are verified, the master SMS opens (and decompresses, if necessary) an upgrade instruction file also included as one of the software components loaded into sub-directory  1220  from the Installation Kit. The upgrade instruction file indicates the scope of the upgrade (i.e., upgrade mode). For instance, the upgrade instruction file may indicate that the upgrade may be hot or cold or must only be cold. The upgrade instruction file may also indicate that the upgrade may be done only across the entire chassis—that is, all applications to be upgraded must be upgraded simultaneously across the entire chassis—or that the upgrade may be done on a board-by-board basis or a path-by-path basis or some other partial chassis upgrade. A board-by-board upgrade may allow a network device administrator to chose certain boards on which to upgrade applications and allow older versions of the same applications to continue running on other boards. Similarly, path-by-path or other service related upgrades may allow the network administrator to chose to upgrade only the applications controlling particular services for particular customers, for example, a single path, while allowing older versions of the applications to continue to control the other services. Various upgrade modes are possible. 
   The upgrade instructions file may also include more detailed instructions such as the order in which each software component should be upgraded. That is, if several applications are to be upgraded, certain ones may need to be upgraded before certain other ones. Similarly, certain software components may need to be upgraded simultaneously. Moreover, certain boards may need to be upgraded prior to other boards. For example, control processor card  12  may need to be upgraded prior to upgrading any line cards. 
   The master SMS then creates a record  1227  ( FIG. 21   b ) in an SMS table  192 , which may also be termed an “image control table.” The record includes at least a logical identification number (LID) field  1226 , a verification status field and an upgrade mode field. Similar to other LIDs described above, LID field  1226  is filled in with a unique LID (e.g.,  9623 ) corresponding to the new release. If the SMS verification of the new release&#39;s software components completed successfully, then the verification status field indicates that verification passed, otherwise an error code is input into the verification status field. The SMS then enters a code in the upgrade mode field from the upgrade instructions file indicating the scope of the upgrade. Alternatively, the SMS table may include a field for each possible type of upgrade mode and the master SMS would input an indication in the field or fields corresponding to possible types of upgrades for the new release. 
   The master SMS may then send a trap to the NMS or the NMS may periodically poll the SMS table to detect new records. In either case, the NMS creates a new record  1230  ( FIG. 21   c ) in an Available Release window  1232 . For security, only certain users, such as administrators, will have access to the Available Release window. Referring to  FIG. 21   d,  to view this window, an administrator accesses a pull down menu, for example, the view pull down menu, and selects an Installation option  1234 . The administrator may select any entry in the Available Release window to cause an Image Control dialog box  1236  ( FIG. 21   e ) to appear. If the user selects a release (old or new) that is not currently running, the user may select a Delete option  1238 , a Re-Verify option  1239  or an Install option  1240  in the Image Control dialog box. Other options may also be available. 
   If the user selects the Install option and multiple upgrade modes are possible for the selected release, then an Upgrade Mode dialog box  1242  ( FIG. 21   f ) will be displayed. The Upgrade Mode dialog box may present only those options available for the chosen release, or the Upgrade Mode dialog box may present all upgrade options but only allow the user to chose the options available for the chosen release. For example, the dialog box may present a Hot option  1243  and a Cold option  1244 . If the upgrade for the chosen release can only be completed as a cold upgrade, then the dialog box may not allow the user to select the Hot option. 
   The Upgrade Mode dialog box may also present other options such as entire chassis  1245 , board-by-board  1246 , path-by-path  1247  or various other upgrade options. If the user selects the board-by-board option or the path-by-path option, other dialog boxes will appear to accept the administrator&#39;s input of which board(s) or path(s) to upgrade. The user may also select a Time for Installation option  1249  and input a particular time for the installation. If the Time for Installation option is not selected, then the default may be to initiate the installation immediately. 
   Once the administrator has provided any required information in the Upgrade Control dialog box and, in the case of an upgrade, the Upgrade Mode dialog box, the NMS creates a new record  1251  in an Upgrade Control table  1248  ( FIG. 21   g ). The NMS inputs the Image LID (e.g.,  9623 ) in Image LID field  1250  of the record in the SMS table corresponding to the release selected by the administrator (e.g., release 1.1) in the Available Release window. The NMS then inputs a code (e.g., x 2344 ) in a Command field  1252  corresponding to the action requested by the administrator. For example, the code may represent a Delete command indicating that the release selected by the administrator should be deleted from both the Install sub-directory and the corresponding record removed from the SMS table. Instead the code may represent a re-verify command indicating that the software components in the Install sub-directory corresponding to the release should be re-verified. Similarly, the code may represent an upgrade command and, specifically, a particular type of upgrade according to the upgrade mode chosen by the user. Alternatively, instead of having codes, the Upgrade Control table could include fields for each command and each upgrade mode and the NMS would fill in the appropriate field(s). The NMS also fills in a Time for Installation field  1253  with a future time or indicates that the installation should proceed immediately. 
   When the NMS adds new record  1251  to the Upgrade Control table, an active query is sent to the master SMS. If an upgrade command is detected in Command field  1252 , the master SMS sends notices to all SMS clients that access software components from the current release sub-directory indicating that software components should now be accessed from the new release sub-directory. SMS clients include, for example, the Master Control Driver (MCD) and the program supervisor module (PSM) within the mission kernel image (MKI) on each board, which the slave SRM on each board may ask to load upgraded software components. Having the SMS clients point to the new sub-directory for the new release eliminates the need for the SRM to have any release specific details. For example, during an ATM upgrade, the slave SRMs will simply ask the local PSM to load ATM software components regardless of the release number, however, since the PSM is pointed to the new release directory, upgraded ATM software components will be loaded. 
   The master SMS then opens up the packing list from the sub-directory (e.g.,  1224 ) of the currently running release (e.g., release 1.0) and the sub-directory (e.g.,  1220 ) of the new release (e.g., release 1.1) and compares the signatures of each software component to determine which software components have changed and, thus, need to be upgraded, and to determine if there are any new software components to be installed. Thus, signatures promote hot upgrades by allowing the SMS to quickly locate only those software components that need to be upgraded. 
   Since signatures are automatically generated for each software component as part of putting together a new release and since a robust signature generating program is used, a quick comparison of two signatures provides an accurate assurance that either the software component has changed or has not. Instead of comparing signatures, a full compare of each running software component against each corresponding software component in the new release may be run, however, since many software components may be quite long (e.g., 50–60 megabytes) this will likely take a considerable amount of time and processor power. Instead, the signatures provide a quick, easy way to accurately determine the upgrade status of each software component. 
   If the new release requires a converted configuration database and this was not implemented through a cold upgrade, then the master SMS will find a script for converted configuration database file  42 ′ in the new release subdirectory. The master SMS may terminate the currently executing configuration database  42  and instantiate converted configuration database  42 ′. 
   Referring to  FIG. 22 , instead of directly upgrading configuration database  42  on central processor  12 , a backup configuration database  420  on a backup central processor  13  may be upgraded first. As described above, computer system  10  includes central processor  12 . Computer system  10  may also include a redundant or backup central processor  13  that mirrors or replicates the active state of central processor  12 . Backup central processor  13  is generally in stand-by mode unless central processor  12  fails at which point a fail-over to backup central processor  13  is initiated to allow the backup central processor to be substituted for central processor  12 . In addition to failures, backup central processor  13  may be used for software and hardware upgrades that require changes to the configuration database. Through backup central processor  13 , upgrades can be made to backup configuration database  420  instead of to configuration database  42 . 
   Master SMS  184  tells slave SMS  186   e  to cause backup processor  13  to change from backup mode to upgrade mode. Slave SMS  186   e  then works with slave SRM  37   e  to cause backup processor  13  to change from backup mode to upgrade mode. In upgrade mode, backup processor  13  stops replicating the active state of central processor  12 . Slave SMS  186   e  then copies over the script for new configuration database file  42 ′ from sub-directory  1220 , executes the script to generate new configuration database  42 ′, directs slave SRM  37   e  to terminate backup configuration database  420  and execute the new configuration database  42 ′. 
   Once configuration database  42 ′ is upgraded, a fail-over or switch-over from central processor  12  to backup central processor  13  is initiated. Central processor  13  then begins acting as the primary central processor and applications running on central processor  13  and other boards throughout computer system  10  begin using upgraded configuration database  42 ′. Central processor  12  may not become the backup central processor right away. Instead, central processor  12  with its older copy of configuration database  42  may stay dormant in case an automatic downgrade is necessary (described below). If the upgrade goes smoothly and is committed (described below), then central processor  12  will begin operating in backup mode and replace old configuration database  42  with new configuration database  42 ′. 
   Existing processes using their view ids and APIs to access new configuration database  42 ′ in the same manner as they accessed old configuration database  42 . However, when new processes (e.g., ATM version two  360  and device driver  362 ,  FIG. 3   c ) access new configuration database  42 ′, their view ids and APIs allow them to access new tables and data within new configuration database  42 ′. 
   Once the configuration database is converted or if no conversion of the configuration database is necessary, the master SMS determines whether any meta data files, such as the PMD file, have been upgraded—that is the signature of a meta data file in the currently running release does not match the signature of the same meta data file in the new release. If yes, then the master SMS overwrites the current meta data files with any changed, new meta data files. New meta data files may also be loaded from the new release sub-directory. 
   Referring to  FIG. 23 , if any other software components have changed, then master SMS  184  first needs to determine where the software components corresponding to the changed software components are currently executing. Since each slave SRM maintains information about which software components are loaded on their local board, the master SMS may call master SRM  36 , which will ask each of the slave SRMs  37   a – 37   n,  or the master SMS may ask each of the slave SMSs  186   a – 186   n,  which will ask their local slave SRMs  37   a – 37   n.  The master SMS upgrades the software components in accordance with the upgrade instructions. Thus, if the upgrade instructions indicate that all instantiations of ATM across the entire chassis should be simultaneously upgraded, then the master SMS initiates and controls a lock step upgrade. In most instances, all instantiations of a distributed application will be upgraded simultaneously to avoid conflicts between the different versions. However, if an upgraded software component is compatible with its corresponding, currently running software component, then the upgrade need not be chassis wide. 
   After determining where software components, that need to be upgraded, are currently being executed, master SMS  184  tells the appropriate slave SMSs, which tell their local slave SRMs (which tell their local PSM within their local MKI, not shown in  FIG. 23  for clarity), to load the changed software components and the control shims for each of the changed software components from new release sub-directory  1220  onto the appropriate boards. For example, if an ATM software component has changed, the master SMS tells slave SMSs  186   b – 186   n,  which tell slave SRMs  37   b – 37   n,  to load ATM control shim (e.g., ATM_V2_Cntrl.exe  204   a – 204   n ) and, for example, an ATM version 2 file (e.g., ATM_V2.exe  206   a – 206   b ) from the new release 1.1. If any control shim has been upgraded, then it must be loaded from the new release, otherwise, it could be loaded from the new release or control shim from the currently executing release could be used. Typically, whether the control shim has changed or not, it is loaded from the new release since the changed software components are also loaded from the new release. If necessary, the slave SRM de-compresses each of the software components. 
   Once loaded, each control shim sends a message to the slave SMS on its board including a list of upgrade instructions. Using the ATM example, ATM control shim  204   a  loaded on line card  16   a  sends a message to slave SMS  186   b  with a list of upgrade instructions. For distributed applications such as ATM, a lock step upgrade is initiated. That is, when each slave SMS receives the upgrade instructions message from the local control shim, it sends a notice to the master SMS. When the master SMS receives notifications from each of the appropriate slave SMSs, the master SMS sends each slave SMS a command to execute the first instruction. Each slave SMS then sends its local control shim the first upgrade instruction from the upgrade instructions message. After executing the first step, each control shim notifies its local slave SMS, which sends a notice to the master SMS that the first step is complete. When all appropriate slave SMSs have indicated that the first step is done, the master SMS sends each slave SMS a command to execute the next step. Again, each slave SMS sends its local control shim the next upgrade instruction from the upgrade instructions message, and again, when each control shim has executed the next step it notifies its local slave SMS, which sends a message to the master SMS indicating the step is complete. This process is repeated until all steps in the upgrade instructions message have been executed. 
   When the last upgrade instruction is completed, the control shim notifies the slave SMSs, which sends a message to the master SMS indicating that the upgrade of that software component is complete. If other software components need to be upgraded, the master SMS then begins a similar upgrade process for those additional software components. Once all the software components are upgraded, the master SMS writes a complete indication in status field  1255  ( FIG. 21   g ) of Upgrade Control table  1248 . The master SMS may then send a trap to the NMS to indicate that the upgrade is complete or the NMS may poll the status field of the Upgrade Control table waiting for a complete status. 
   The first step in the upgrade instructions may be to stall the currently executing software component. In the above example, each line card is shown implementing one instance of ATM, but as explained below, multiple instances of ATM may be executed on each line card. Another upgrade instruction may cause the upgraded versions of ATM  204   a – 204   n  to retrieve active state from the current versions of ATM  188   a – 188   n.  The retrieval of active state can be accomplished in the same manner that a redundant or backup instantiation of ATM retrieves active state from the primary instantiation of ATM. When the upgraded instances of ATM are executing and updated with active state, the next upgrade instruction may be to switchover to the upgraded version and terminate the version that was executing. A “lock step upgrade” indicates that each line card executing a particular software component, such as ATM, is switched over to the software component simultaneously. 
   There may be upgrades that require changes to multiple applications and to the APIs for those applications. For example, a new feature may be added to ATM that also requires additional functionality to be added to the Multi-Protocol Label Switching (MPLS) application. The additional functionality may change the peer-to-peer API for ATM, the peer-to-peer API for MPLS and the API between ATM and MPLS. In this scenario, the upgrade operation must avoid allowing the “new” version of ATM to communicate with “old” version of ATM or the “old” version of MPLS and vice versa. The master SMS will use the upgrade instructions file to determine the requirements for the individual upgrade. Again, the SMS would implement the upgrade in a lock step fashion. All instances of ATM and MPLS would be upgraded together. The simultaneous switchover to new versions of both MPLS and ATM eliminate any API compatibility errors. 
   The upgrade of an ATM software component described above is by way of example, and it should be understood that the upgrade of other software components, such as device drivers, would be accomplished in the same manner. 
   Instead of storing all software components from a new release in the new release sub-directory, only the changed software components may be stored. That is, the master SMS could open the packaging list in the currently executing release and compare the signatures of the components in that packaging list to the signatures of the software components in the packaging list for the new release and remove any software components that had not changed. If all the software components of a new release are not saved in the new sub-directory and if an old release is deleted, however, those software components that had not been upgraded would need to be copied from the old release sub-directory into the new release sub-directory prior to the deletion. 
   Instead of using the full signatures generated by the signature generating program, the full signatures may be converted into simple easy to read version numbers. To accomplish this, however, a conversion database would need to be maintained which would associate each signature with a version number. This could be an automatic process, such that each time a software component signature is generated, the signature could be compared with all those in the conversion database. If it is already listed, then the software component did not change and the version number associated with the signature in the conversion database would be appended to the software component instead of the full signature. If the signature is not listed, a new version number would be automatically generated, added to the conversion database along with the new signature and then appended to the new software component. Since software components may be changed quite often, the conversion database may become quite large. In addition, a conversion database may need to be kept for each software component to insure that in the unlikely event that two signatures from different software components matched, the same version number isn&#39;t assigned to two different software components. 
   Once all software components have been upgraded, any new hardware received by the user of computer system  10  may be inserted. The MCD would find information related to the new hardware in the new PMD file and the newly available MKI and any necessary device drivers and applications would be loaded. 
   Automatic Downgrade: 
   Often, implementation of an upgrade, can cause unexpected errors in the upgraded software, in other applications or in hardware. As described above, a new configuration database  42 ′ ( FIG. 20 ) is generated and changes to the new configuration database are made in new tables (e.g., ATM interface table  114 ′ and ATM group table  108 ′,  FIG. 20 ) and new executable files (e.g., ATMv2.exe  189 , ATMv2_cntrl.exe  190  and ATMv2_cnfg_cntrl.exe  191 ) are downloaded to memory  40 . Importantly, the old configuration database records and the original application files are not deleted or altered. In the embodiment where changes are made directly to configuration database  42  on central processor  12 , they are made only in non-persistent memory until committed (described below). In the embodiment where changes are made to backup configuration database  420  on backup central processor  13 , original configuration database  42  remains unchanged. 
   Because the operating system provides a protected memory model that assigns different process blocks to different processes, including upgraded applications, the original applications will not share memory space with the upgraded applications and, therefore, cannot corrupt or change the memory used by the original application. Similarly, memory  40  is capable of simultaneously maintaining the original and upgraded versions of the configuration database records and executable files as well as the original and upgraded versions of the applications (e.g., ATM  188   a – 188   n ). As a result, the SMS is capable of an automatic downgrade on the detection of an error. To allow for automatic downgrade, the SRMs pass error information to the SMS. The SMS may cause the system to revert to the old configuration and application (i.e., automatic downgrade) on any error or only for particular errors. 
   As mentioned, often upgrades to one application may cause unexpected faults or errors in other software. If the problem causes a system shut down and the configuration upgrade was stored in persistent storage, then the system, when powered back up, will experience the error again and shut down again. Since, the upgrade changes to the configuration database are not copied to persistent storage  21  until the upgrade is committed, if the computer system is shut down, when it is powered back up, it will use the original version of the configuration database and the original executable files, that is, the computer system will experience an automatic downgrade. 
   Additionally, a fault induced by an upgrade may cause the system to hang, that is, the computer system will not shut down but will also become inaccessible by the NMS and inoperable. To address this concern, in one embodiment, the NMS and the master SMS periodically send messages to each other indicating they are executing appropriately. If the SMS does not receive one of these messages in a predetermined period of time, then the SMS knows the system has hung. The master SMS may then tell the slave SMSs to revert to the old configuration (i.e., previously executing copies of ATM  188   a – 188   n ) and if that does not work, the master SMS may re-start/re-boot computer system  10 . Again, because the configuration changes were not saved in persistent storage, when the computer system powers back up, the old configuration will be the one implemented. 
   Evaluation Mode: 
   Instead of implementing a change to a distributed application across the entire computer system, an evaluation mode allows the SMS to implement the change in only a portion of the computer system. If the evaluation mode is successful, then the SMS may fully implement the change system wide. If the evaluation mode is unsuccessful, then service interruption is limited to only that portion of the computer system on which the upgrade was deployed. In the above example, instead of executing the upgraded ATMv2  189  on each of the line cards, the ATMv2 configuration convert file  191  will create an ATMv2 group table  108 ′ indicating an upgrade only to one line card, for example, line card  16   a.  Moreover, if multiple instantiations of ATM are running on line card  16   a  (e.g., one instantiation per port), the ATMv2 configuration convert file may indicate through ATMv2 interface table  114 ′ that the upgrade is for only one instantiation (e.g., one port) on line card  16   a.  Consequently, a failure is likely to only disrupt service on that one port, and again, the SMS can further minimize the disruption by automatically downgrading the configuration of that port on the detection of an error. If no error is detected during the evaluation mode, then the upgrade can be implemented over the entire computer system. 
   Upgrade Commitment: 
   Upgrades are made permanent by saving the new application software and new configuration database and DDL file in persistent storage and removing the old configuration data from memory  40  as well as persistent storage. As mentioned above, changes may be automatically saved in persistent storage as they are made in non-persistent memory (no automatic downgrade), or the user may choose to automatically commit an upgrade after a successful time interval lapses (evaluation mode). The time interval from upgrade to commitment may be significant. During this time, configuration changes may be made to the system. Since these changes are typically made in non-persistent memory, they will be lost if the system is rebooted prior to upgrade commitment. Instead, to maintain the changes, the user may request that certain configuration changes made prior to upgrade commitment be copied into the old configuration database in persistent memory. Alternatively, the user may choose to manually commit the upgrade at his or her leisure. In the manual mode, the user would ask the NMS to commit the upgrade and the NMS would inform the master SMS, for example, through a record in the SMS table. 
   Independent Process Failure and Restart: 
   Depending upon the fault policy managed by the slave SRMs on each board, the failure of an application or device driver may not immediately cause an automatic downgrade during an upgrade process. Similarly, the failure of an application or device driver during normal operation may not immediately cause the fail over to a backup or redundant board. Instead, the slave SRM running on the board may simply restart the failing process. After multiple failures by the same process, the fault policy may cause the SRM to take more aggressive measures such as automatic downgrade or fail-over. 
   Referring to  FIG. 24 , if an application, for example, ATM application  230  fails, the slave SRM on the same board as ATM  230  may simply restart it without having to reboot the entire system. As described above, under the protected memory model, a failing process cannot corrupt the memory blocks used by other processes. Typically, an application and its corresponding device drivers would be part of the same memory block or even part of the same software program, such that if the application failed, both the application and device drivers would need to be restarted. Under the modular software architecture, however, applications, for example ATM application  230 , are independent of the device drivers, for example, ATM driver  232  and Device Drivers (DD)  234   a – 234   c.  This separation of the data plane (device drivers) and control plane (applications) results in the device drivers being peers of the applications. Hence, while the ATM application is terminated and restarted, the device drivers continue to function. 
   For network devices, this separation of the control plane and data plane means that the connections previously established by the ATM application are not lost when ATM fails and hardware controlled by the device drivers continue to pass data through connections previously established by the ATM application. Until the ATM application is restarted and re-synchronized (e.g., through an audit process, described below) with the active state of the device drivers, no new network connections may be established but the device drivers continue to pass data through the previously established connections to allow the network device to minimize disruption and maintain high availability. 
   Local Backup: 
   If a device driver, for example, device driver  234 , fails instead of an application, for example, ATM  230 , then data cannot be passed. For a network device, it is critical to continue to pass data and not lose network connections. Hence, the failed device driver must be brought back up (i.e., recovered) as soon as possible. In addition, the failing device driver may have corrupted the hardware it controls, therefore, that hardware must be reset and reinitialized. The hardware may be reset as soon as the device driver terminates or the hardware may be reset later when the device driver is restarted. Resetting the hardware stops data flow. In some instances, therefore, resetting the hardware will be delayed until the device driver is restarted to minimize the time period during which data is not flowing. Alternatively, the failing device driver may have corrupted the hardware, thus, resetting the hardware as soon as the device driver is terminated may be important to prevent data corruption. In either case, the device driver re-initializes the hardware during its recovery. 
   Again, because applications and device drivers are assigned independent memory blocks, a failed device driver can be restarted without having to restart associated applications and device drivers. Independent recovery may save significant time as described above for applications. In addition, restoring the data plane (i.e., device drivers) can be simpler and faster than restoring the control plane (i.e., applications). While it may be just as challenging in terms of raw data size, device driver recovery may simply require that critical state data be copied into place in a few large blocks, as opposed to application recovery which requires the successive application of individual configuration elements and considerable parsing, checking and analyzing. In addition, the application may require data stored in the configuration database on the central processor or data stored in the memory of other boards. The configuration database may be slow to access especially since many other applications also access this database. The application may also need time to access a management information base (MIB) interface. 
   To increase the speed with which a device driver is brought back up, the restarted device driver program accesses local backup  236 . In one example, local backup is a simple storage/retrieval process that maintains the data in simple lists in physical memory (e.g., random access memory, RAM) for quick access. Alternatively, local backup may be a database process, for example, a Polyhedra database, similar to the configuration database. 
   Local backup  236  stores the last snap shot of critical state information used by the original device driver before it failed. The data in local backup  236  is in the format required by the device driver. In the case of a network device, local back up data may include path information, for example, service endpoint, path width and path location. Local back up data may also include virtual interface information, for example, which virtual interfaces were configured on which paths and virtual circuit (VC) information, for example, whether each VC is switched or passed through segmentation and reassembly (SAR), whether each VC is a virtual channel or virtual path and whether each VC is multicast or merge. The data may also include traffic parameters for each VC, for example, service class, bandwidth and/or delay requirements. 
   Using the data in the local backup allows the device driver to quickly recover. An Audit process resynchronizes the restarted device driver with associated applications and other device drivers such that the data plane can again transfer network data. Having the backup be local reduces recovery time. Alternatively, the backup could be stored remotely on another board but the recovery time would be increased by the amount of time required to download the information from the remote location. 
   Audit Process: 
   It is virtually impossible to ensure that a failed process is synchronized with other processes when it restarts, even when backup data is available. For example, an ATM application may have set up or torn down a connection with a device driver but the device driver failed before it updated corresponding backup data. When the device driver is restarted, it will have a different list of established connections than the corresponding ATM application (i.e., out of synchronization). The audit process allows processes like device drivers and ATM applications to compare information, for example, connection tables, and resolve differences. For instance, connections included in the driver&#39;s connection table and not in the ATM connection table were likely torn down by ATM prior to the device driver crash and are, therefore, deleted from the device driver connection table. Connections that exist in the ATM connection table and not in the device driver connection table were likely set up prior to the device driver failure and may be copied into the device driver connection table or deleted from the ATM connection table and re-set up later. If an ATM application fails and is restarted, it must execute an audit procedure with its corresponding device driver or drivers as well as with other ATM applications since this is a distributed application. 
   Vertical Fault Isolation: 
   Typically, a single instance of an application executes on a single card or in a system. Fault isolation, therefore, occurs at the card level or the system level, and if a fault occurs, an entire card—and all the ports on that card—or the entire system—and all the ports in the system—is affected. In a large communications platform, thousands of customers may experience service outages due to a single process failure. 
   For resiliency and fault isolation one or more instances of an application and/or device driver may be started per port on each line card. Multiple instances of applications and device drivers are more difficult to manage and require more processor cycles than a single instance of each but if an application or device driver fails, only the port those processes are associated with is affected. Other applications and associated ports—as well as the customers serviced by those ports—will not experience service outages. Similarly, a hardware failure associated with only one port will only affect the processes associated with that port. This is referred to as vertical fault isolation. 
   Referring to  FIG. 25 , as one example, line card  16   a  is shown to include four vertical stacks  400 ,  402 ,  404 , and  406 . Vertical stack  400  includes one instance of ATM  110  and one device driver  43   a  and is associated with port  44   a.  Similarly, vertical stacks  402 ,  404  and  406  include one instance of ATM  111 ,  112 ,  113  and one device driver  43   b,    43   c,    43   d,  respectively and each vertical stack is associated with a separate port  44   b,    44   c,    44   d,  respectively. If ATM  112  fails, then only vertical stack  404  and its associated port  44   c  are affected. Service is not disrupted on the other ports (ports  44   a,    44   b,    44   d ) since vertical stacks  400 ,  402 , and  406  are unaffected and the applications and drivers within those stacks continue to execute and transmit data. Similarly, if device driver  43   b  fails, then only vertical stack  402  and its associated port  44   b  are affected. 
   Vertical fault isolation allows processes to be deployed in a fashion supportive of the underlying hardware architecture and allows processes associated with particular hardware (e.g., a port) to be isolated from processes associated with other hardware (e.g., other ports) on the same or a different line card. Any single hardware or software failure will affect only those customers serviced by the same vertical stack. Vertical fault isolation provides a fine grain of fault isolation and containment. In addition, recovery time is reduced to only the time required to re-start a particular application or driver instead of the time required to re-start all the processes associated with a line card or the entire system. 
   Fault/Event Detection: 
   Traditionally, fault detection and monitoring does not receive a great deal of attention from network equipment designers. Hardware components are subjected to a suite of diagnostic tests when the system powers up. After that, the only way to detect a hardware failure is to watch for a red light on a board or wait for a software component to fail when it attempts to use the faulty hardware. Software monitoring is also reactive. When a program fails, the operating system usually detects the failure and records minimal debug information. 
   Current methods provide only sporadic coverage for a narrow set of hard faults. Many subtler failures and events often go undetected. For example, hardware components sometimes suffer a minor deterioration in functionality, and changing network conditions stress the software in ways that were never expected by the designers. At times, the software may be equipped with the appropriate instrumentation to detect these problems before they become hard failures, but even then, network operators are responsible for manually detecting and repairing the conditions. 
   Systems with high availability goals must adopt a more proactive approach to fault and event monitoring. In order to provide comprehensive fault and event detection, different hierarchical levels of fault/event management software are provided that intelligently monitor hardware and software and proactively take action in accordance with a defined fault policy. A fault policy based on hierarchical scopes ensures that for each particular type of failure the most appropriate action is taken. This is important because over-reacting to a failure, for example, re-booting an entire computer system or re-starting an entire line card, may severely and unnecessarily impact service to customers not affected by the failure, and under-reacting to failures, for example, restarting only one process, may not completely resolve the fault and lead to additional, larger failures. Monitoring and proactively responding to events may also allow the computer system and network operators to address issues before they become failures. For example, additional memory may be assigned to programs or added to the computer system before a lack of memory causes a failure. 
   Hierarchical Scopes and Escalation: 
   Referring to  FIG. 26 , in one embodiment, master SRM  36  serves as the top hierarchical level fault/event manager, each slave SRM  37   a – 37   n  serves as the next hierarchical level fault/event manager, and software applications resident on each board, for example, ATM  110 – 113  and device drivers  43   a – 43   d  on line card  16   a  include sub-processes that serve as the lowest hierarchical level fault/event managers (i.e., local resiliency managers, LRM). Master SRM  36  downloads default fault policy (DFP) files (metadata)  430   a – 430   n  from persistent storage to memory  40 . Master SRM  36  reads a master default fault policy file (e.g., DFP  430   a ) to understand its fault policy, and each slave SRM  37   a – 37   n  downloads a default fault policy file (e.g., DFP  430   b – 430   n ) corresponding to the board on which the slave SRM is running. Each slave SRM then passes to each LRM a fault policy specific to each local process. 
   A master logging entity  431  also runs on central processor  12  and slave logging entities  433   a – 433   n  run on each board. Notifications of failures and other events are sent by the master SRM, slave SRMs and LRMs to their local logging entity which then notifies the master logging entity. The master logging entity enters the event in a master event log file  435 . Each local logging entity may also log local events in a local event log file  435   a – 435   n.    
   In addition, a fault policy table  429  may be created in configuration database  42  by the NMS when the user wishes to over-ride some or all of the default fault policy (see configurable fault policy below), and the master and slave SRMs are notified of the fault policies through the active query process. 
   Referring to  FIG. 27 , as one example, ATM application  110  includes many sub-processes including, for example, an LRM program  436 , a Private Network-to-Network Interface (PNNI) program  437 , an Interim Link Management Interface (ILMI) program  438 , a Service Specific Connection Oriented Protocol (SSCOP) program  439 , and an ATM signaling (SIG) program  440 . ATM application  110  may include many other sub-programs only a few have been shown for convenience. Each sub-process may also include sub-processes, for example, ILMI sub-processes  438   a – 438   n.  In general, the upper level application (e.g., ATM  110 ) is assigned a process memory block that is shared by all its sub-processes. 
   If, for example, SSCOP  439  detects a fault, it notifies LRM  436 . LRM  436  passes the fault to local slave SRM  37   b , which catalogs the fault in the ATM application&#39;s fault history and sends a notice to local slave logging entity  433   b.  The slave logging entity sends a notice to master logging entity  431 , which may log the event in master log event file  435 . The local logging entity may also log the failure in local event log  435   a.  LRM  436  also determines, based on the type of failure, whether it can fully resolve the error and do so without affecting other processes outside its scope, for example, ATM  111 – 113 , device drivers  43   a – 43   d  and their sub-processes and processes running on other boards. If yes, then the LRM takes corrective action in accordance with its fault policy. Corrective action may include restarting SSCOP  439  or resetting it to a known state. 
   Since all sub-processes within an application, including the LRM sub-process, share the same memory space, it may be insufficient to restart or reset a failing sub-process (e.g., SSCOP  439 ). Hence, for most failures, the fault policy will cause the LRM to escalate the failure to the local slave SRM. In addition, many failures will not be presented to the LRM but will, instead, be presented directly to the local slave SRM. These failures are likely to have been detected by either processor exceptions, OS errors or low-level system service errors. Instead of failures, however, the sub-processes may notify the LRM of events that may require action. For example, the LRM may be notified that the PNNI message queue is growing quickly. The LRM&#39;s fault policy may direct it to request more memory from the operating system. The LRM will also pass the event to the local slave SRM as a non-fatal fault. The local slave SRM will catalog the event and log it with the local logging entity, which may also log it with the master logging entity. The local slave SRM may take more severe action to recover from an excessive number of these non-fatal faults that result in memory requests. 
   If the event or fault (or the actions required to handle either) will affect processes outside the LRM&#39;s scope, then the LRM notifies slave SRM  37   b  of the event or failure. In addition, if the LRM detects and logs the same failure or event multiple times and in excess of a predetermined threshold set within the fault policy, the LRM may escalate the failure or event to the next hierarchical scope by notifying slave SRM  37   b . Alternatively or in addition, the slave SRM may use the fault history for the application instance to determine when a threshold is exceeded and automatically execute its fault policy. 
   When slave SRM  37   b  detects or is notified of a failure or event, it notifies slave logging entity  435   b.  The slave logging entity notifies master logging entity  431 , which may log the failure or event in master event log  435 , and the slave logging entity may also log the failure or event in local event log  435   b.  Slave SRM  37   b  also determines, based on the type of failure or event, whether it can handle the error without affecting other processes outside its scope, for example, processes running on other boards. If yes, then slave SRM  37   b  takes corrective action in accordance with its fault policy and logs the fault. Corrective action may include re-starting one or more applications on line card  16   a.    
   If the fault or recovery actions will affect processes outside the slave SRM&#39;s scope, then the slave SRM notifies master SRM  36 . In addition, if the slave SRM has detected and logged the same failure multiple times and in excess of a predetermined threshold, then the slave SRM may escalate the failure to the next hierarchical scope by notifying master SRM  36  of the failure. Alternatively, the master SRM may use its fault history for a particular line card to determine when a threshold is exceeded and automatically execute its fault policy. 
   When master SRM  36  detects or receives notice of a failure or event, it notifies slave logging entity  433   a,  which notifies master logging entity  431 . The master logging entity  431  may log the failure or event in master log file  435  and the slave logging entity may log the failure or event in local event log  435   a.  Master SRM  36  also determines the appropriate corrective action based on the type of failure or event and its fault policy. Corrective action may require failing-over one or more line cards  16   a – 16   n  or other boards, including central processor  12 , to redundant backup boards or, where backup boards are not available, simply shutting particular boards down. Some failures may require the master SRM to re-boot the entire computer system. 
   An example of a common error is a memory access error. As described above, when the slave SRM starts a new instance of an application, it requests a protected memory block from the local operating system. The local operating systems assign each instance of an application one block of local memory and then program the local memory management unit (MMU) hardware with which processes have access (read and/or write) to each block of memory. An MMU detects a memory access error when a process attempts to access a memory block not assigned to that process. This type of error may result when the process generates an invalid memory pointer. The MMU prevents the failing process from corrupting memory blocks used by other processes (i.e., protected memory model) and sends a hardware exception to the local processor. A local operating system fault handler detects the hardware exception and determines which process attempted the invalid memory access. The fault handler then notifies the local slave SRM of the hardware exception and the process that caused it. The slave SRM determines the application instance within which the fault occurred and then goes through the process described above to determine whether to take corrective action, such as restarting the application, or escalate the fault to the master SRM. 
   As another example, a device driver, for example, device driver  43   a  may determine that the hardware associated with its port, for example, port  44   a,  is in a bad state. Since the failure may require the hardware to be swapped out or failed-over to redundant hardware or the device driver itself to be re-started, the device driver notifies slave SRM  37   b . The slave SRM then goes through the process described above to determine whether to take corrective action or escalate the fault to the master SRM. 
   As a third example, if a particular application instance repeatedly experiences the same software error but other similar application instances running on different ports do not experience the same error, the slave SRM may determine that it is likely a hardware error. The slave SRM would then notify the master SRM which may initiate a fail-over to a backup board or, if no backup board exists, simply shut down that board or only the failing port on that board. Similarly, if the master SRM receives failure reports from multiple boards indicating Ethernet failures, the master SRM may determine that the Ethernet hardware is the problem and initiate a fail-over to backup Ethernet hardware. 
   Consequently, the failure type and the failure policy determine at what scope recovery action will be taken. The higher the scope of the recovery action, the larger the temporary loss of services. Speed of recovery is one of the primary considerations when establishing a fault policy. Restarting a single software process is much faster than switching over an entire board to a redundant board or re-booting the entire computer system. When a single process is restarted, only a fraction of a card&#39;s services are affected. Allowing failures to be handled at appropriate hierarchical levels avoids unnecessary recovery actions while ensuring that sufficient recovery actions are taken, both of which minimize service disruption to customers. 
   Hierarchical Descriptors: 
   Hierarchical descriptors may be used to provide information specific to each failure or event. The hierarchical descriptors provide granularity with which to report faults, take action based on fault history and apply fault recovery policies. The descriptors can be stored in master event log file  435  or local event log files  435   a – 435   n  through which faults and events may be tracked and displayed to the user and allow for fault detection at a fine granular level and proactive response to events. In addition, the descriptors can be matched with descriptors in the fault policy to determine the recovery action to be taken. 
   Referring to  FIG. 28 , in one embodiment, a descriptor  441  includes a top hierarchical class field  442 , a next hierarchical level sub-class field  444 , a lower hierarchical level type field  446  and a lowest level instance field  448 . The class field indicates whether the failure or event is related (or suspected to relate) to hardware or software. The subclass field categorizes events and failures into particular hardware or software groups. For example, under the hardware class, subclass indications may include whether the fault or event is related to memory, Ethernet, switch fabric or network data transfer hardware. Under the software class, subclass indications may include whether the fault or event is a system fault, an exception or related to a specific application, for example, ATM. 
   The type field more specifically defines the subclass failure or event. For example, if a hardware class, Ethernet subclass failure has occurred, the type field may indicate a more specific type of Ethernet failure, for instance, a cyclic redundancy check (CRC) error or a runt packet error. Similarly, if a software class, ATM failure or event has occurred, the type field may indicate a more specific type of ATM failure or event, for instance, a private network-to-network interface (PNNI) error or a growing message queue event. The instance field identifies the actual hardware or software that failed or generated the event. For example, with regard to a hardware class, Ethernet subclass, CRC type failure, the instance indicates the actual Ethernet port that experienced the failure. Similarly, with regard to a software class, ATM subclass, PNNI type, the instance indicates the actual PNNI sub-program that experienced the failure or generated the event. 
   When a fault or event occurs, the hierarchical scope that first detects the failure or event creates a descriptor by filling in the fields described above. In some cases, however, the Instance field is not applicable. The descriptor is sent to the local logging entity, which may log it in the local event log file before notifying the master logging entity, which may log it in the master event log file  435 . The descriptor may also be sent to the local slave SRM, which tracks fault history based on the descriptor contents per application instance. If the fault or event is escalated, then the descriptor is passed to the next higher hierarchical scope. 
   When slave SRM  37   b  receives the fault/event notification and the descriptor, it compares it to descriptors in the fault policy for the particular scope in which the fault occurred looking for a match or a best case match which will indicate the recovery procedure to follow. Fault descriptors within the fault policy can either be complete descriptors or have wildcards in one or more fields. Since the descriptors are hierarchical from left to right, wildcards in descriptor fields only make sense from right to left. The fewer the fields with wildcards, the more specific the descriptor. For example, a particular fault policy may apply to all software faults and would, therefore, include a fault descriptor having the class field set to “software” and the remaining fields—subclass, type, and instance—set to wildcard or “match all.” The slave SRM searches the fault policy for the best match (i.e., the most fields matched) with the descriptor to determine the recovery action to be taken. 
   Configurable Fault Policy: 
   In actual use, a computer system is likely to encounter scenarios that differ from those in which the system was designed and tested. Consequently, it is nearly impossible to determine all the ways in which a computer system might fail, and in the face of an unexpected error, the default fault policy that was shipped with the computer system may cause the hierarchical scope (master SRM, slave SRM or LRM) to under-react or over-react. Even for expected errors, after a computer system ships, certain recovery actions in the default fault policy may be determined to be over aggressive or too lenient. Similar issues may arise as new software and hardware is released and/or upgraded. 
   A configurable fault policy allows the default fault policy to be modified to address behavior specific to a particular upgrade or release or to address behavior that was learned after the implementation was released. In addition, a configurable fault policy allows users to perform manual overrides to suit their specific requirements and to tailor their policies based on the individual failure scenarios that they are experiencing. The modification may cause the hierarchical scope to react more or less aggressively to particular known faults or events, and the modification may add recovery actions to handle newly learned faults or events. The modification may also provide a temporary patch while a software or hardware upgrade is developed to fix a particular error. 
   If an application runs out of memory space, it notifies the operating system and asks for more memory. For certain applications, this is standard operating procedure. As an example, an ATM application may have set up a large number of virtual circuits and to continue setting up more, additional memory is needed. For other applications, a request for more memory indicates a memory leak error. The fault policy may require that the application be re-started causing some service disruption. It may be that re-starting the application eventually leads to the same error due to a bug in the software. In this instance, while a software upgrade to fix the bug is developed, a temporary patch to the fault policy may be necessary to allow the memory leak to continue and prevent repeated application re-starts that may escalate to line card re-start or fail-over and eventually to a re-boot of the entire computer system. A temporary patch to the default fault policy may simply allow the hierarchical scope, for example, the local resiliency manager or the slave SRM, to assign additional memory to the application. Of course, an eventual re-start of the application is likely to be required if the application&#39;s leak consumes too much memory. 
   A temporary patch may also be needed while a hardware upgrade or fix is developed for a particular hardware fault. For instance, under the default fault policy, when a particular hardware fault occurs, the recovery policy may be to fail-over to a backup board. If the backup board includes the same hardware with the same hardware bug, for example, a particular semiconductor chip, then the same error will occur on the backup board. To prevent a repetitive fail-over while a hardware fix is developed, the temporary patch to the default fault policy may be to restart the device driver associated with the particular hardware instead of failing-over to the backup board. 
   In addition to the above needs, a configurable fault policy also allows purchasers of computer system  10  (e.g., network service providers) to define their own policies. For example, a network service provider may have a high priority customer on a particular port and may want all errors and events (even minor ones) to be reported to the NMS and displayed to the network manager. Watching all errors and events might give the network manager early notice of growing resource consumption and the need to plan to dedicate additional resources to this customer. 
   As another example, a user of computer system  10  may want to be notified when any process requests more memory. This may give the user early notice of the need to add more memory to their system or to move some customers to different line cards. 
   Referring again to  FIG. 26 , to change the default fault policy as defined by default fault policy (DFP) files  430   a – 430   n,  a configuration fault policy file  429  is created by the NMS in the configuration database. An active query notification is sent by the configuration database to the master SRM indicating the changes to the default fault policy. The master SRM notifies any slave SRMs of any changes to the default fault policies specific to the boards on which they are executing, and the slave SRMs notify any LRMs of any changes to the default fault policies specific to their process. Going forward, the default fault policies—as modified by the configuration fault policy—are used to detect, track and respond to events or failures. 
   Alternatively, active queries may be established with the configuration database for configuration fault policies specific to each board type such that the slave SRMs are notified directly of changes to their default fault policies. 
   A fault policy (whether default or configured) is specific to a particular scope and descriptor and indicates a particular recovery action to take. As one example, a temporary patch may be required to handle hardware faults specific to a known bug in an integrated circuit chip. The configured fault policy, therefore, may indicate a scope of all line cards, if the component is on all line cards, or only a specific type of line card that includes that component. The configured fault policy may also indicate that it is to be applied to all hardware faults with that scope, for example, the class will indicate hardware (HW) and all other fields will include wildcards (e.g., HW.*.*.*). Instead, the configured fault policy may only indicate a particular type of hardware failure, for example, CRC errors on transmitted Ethernet packets (e.g., HW.Ethernet.TxCRC.*). 
   Redundancy: 
   As previously mentioned, a major concern for service providers is network downtime. In pursuit of “five 9&#39;s availability” or 99.999% network up time, service providers must minimize network outages due to equipment (i.e., hardware) and all too common software failures. Developers of computer systems often use redundancy measures to minimize downtime and enhance system resiliency. Redundant designs rely on alternate or backup resources to overcome hardware and/or software faults. Ideally, the redundancy architecture allows the computer system to continue operating in the face of a fault with minimal service disruption, for example, in a manner transparent to the service provider&#39;s customer. 
   Generally, redundancy designs come in two forms: 1:1 and 1:N. In a so-called “1:1 redundancy” design, a backup element exists for every active or primary element (i.e., hardware backup). In the event that a fault affects a primary element, a corresponding backup element is substituted for the primary element. If the backup element has not been in a “hot” state (i.e., software backup), then the backup element must be booted, configured to operate as a substitute for the failing element, and also provided with the “active state” of the failing element to allow the backup element to take over where the failed primary element left off. The time required to bring the software on the backup element to an “active state” is referred to as synchronization time. A long synchronization time can significantly disrupt system service, and in the case of a computer network device, if synchronization is not done quickly enough, then hundreds or thousands of network connections may be lost which directly impacts the service provider&#39;s availability statistics and angers network customers. 
   To minimize synchronization time, many 1:1 redundancy schemes support hot backup of software, which means that the software on the backup elements mirror the software on the primary elements at some level. The “hotter” the backup element—that is, the closer the backup mirrors the primary—the faster a failed primary can be switched over or failed over to the backup. The “hottest” backup element is one that runs hardware and software simultaneously with a primary element conducting all operations in parallel with the primary element. This is referred to as a “1+1 redundancy” design and provides the fastest synchronization. 
   Significant costs are associated with 1:1 and 1+1 redundancy. For example, additional hardware costs may include duplicate memory components and printed circuit boards including all the components on those boards. The additional hardware may also require a larger supporting chassis. Space is often limited, especially in the case of network service providers who may maintain hundreds of network devices. Although 1:1 redundancy improves system reliability, it decreases service density and decreases the mean time between failures. Service density refers to the proportionality between the net output of a particular device and its gross hardware capability. Net output, in the case of a network device (e.g., switch or router), might include, for example, the number of calls handled per second. Redundancy adds to gross hardware capability but not to the net output and, thus, decreases service density. Adding hardware increases the likelihood of a failure and, thus, decreases the mean time between failures. Likewise, hot backup comes at the expense of system power. Each active element consumes some amount of the limited power available to the system. In general, the 1+1 or 1:1 redundancy designs provide the highest reliability but at a relatively high cost. Due to the importance of network availability, most network service providers prefer the 1+1 redundancy design to minimize network downtime. 
   In a 1:N redundancy design, instead of having one backup element per primary element, a single backup element or spare is used to backup multiple (N) primary elements. As a result, the 1:N design is generally less expensive to manufacture, offers greater service density and better mean time between failures than the 1:1 design and requires a smaller chassis/less space than a 1:1 design. One disadvantage of such a system, however, is that once a primary element fails over to the backup element, the system is no longer redundant (i.e., no available backup element for any primary element). Another disadvantage relates to hot state backup. Because one backup element must support multiple primary elements, the typical 1:N design provides no hot state on the backup element leading to long synchronization times and, for network devices, the likelihood that connections will be dropped and availability reduced. 
   Even where the backup element provides some level of hot state backup it generally lacks the processing power and memory to provide a full hot state backup (i.e., 1+N) for all primary elements. To enable some level of hot state backup for each primary element, the backup element is generally a “mega spare” equipped with a more powerful processor and additional memory. This requires customers to stock more hardware than in a design with identical backup and primary elements. For instance, users typically maintain extra hardware in the case of a failure. If a primary fails over to the backup, the failed primary may be replaced with a new primary. If the primary and backup elements are identical, then users need only stock that one type of board, that is, a failed backup is also replaced with the same hardware used to replace the failed primary. If they are different, then the user must stock each type of board, thereby increasing the user&#39;s cost. 
   Distributed Redundancy: 
   A distributed redundancy architecture spreads software backup (hot state) across multiple elements. Each element may provide software backup for one or more other elements. For software backup alone, therefore, the distributed redundancy architecture eliminates the need for hardware backup elements (i.e., spare hardware). Where hardware backup is also provided, spreading resource demands across multiple elements makes it possible to have significant (perhaps full) hot state backup without the need for a mega spare. Identical backup (spare) and primary hardware provides manufacturing advantages and customer inventory advantages. A distributed redundancy design is less expensive than many 1:1 designs and a distributed redundancy architecture also permits the location of the hardware backup element to float, that is, if a primary element fails over to the backup element, when the failed primary element is replaced, that new hardware may serve as the hardware backup. 
   Software Redundancy: 
   In its simplest form, a distributed redundancy system provides software redundancy (i.e., backup) with or without redundant (i.e., backup) hardware, for example, with or without using backup line card  16   n  as discussed earlier with reference to the logical to physical card table ( FIG. 14   b ). Referring to  FIG. 29 , computer system  10  includes primary line cards  16   a,    16   b  and  16   c.  Computer system  10  will likely include additional primary line cards; only three are discussed herein (and shown in  FIG. 29 ) for convenience. As described above, to load instances of software applications, the NMS creates software load records (SLR)  128   a – 128   n  in configuration database  42 . The SLR includes the name of a control shim executable file and a logical identification (LID) associated with a primary line card on which the application is to be spawned. In the current example, there either are no hardware backup line cards or, if there are, the slave SRM executing on that line card does not download and execute backup applications. 
   As one example, NMS  60  creates SLR  128   a  including the executable name atm_cntrl.exe and card LID  30  (line card  16   a ), SLR  128   b  including atm_cntrl.exe and LID  31  (line card  16   b ) and SLR  128   c  including atm_cntrl.exe and LID  32  (line card  16   c ). The configuration database detects LID  30 ,  31  and  32  in SLRs  128   a ,  128   b  and  128   c,  respectively, and sends slave SRMs  37   b,    37   c  and  37   d  (line cards  16   a,    16   b,  and  16   c ) notifications including the name of the executable file (e.g., atm_cntrl.exe) to be loaded. The slave SRMs then download and execute a copy of atm_cntrl.exe  135  from memory  40  to spawn ATM controllers  136   a,    136   b  and  136   c.    
   Through the active query feature, the ATM controllers are sent records from group table (GT)  108 ′ ( FIG. 30 ) indicating how many instances of ATM each must start on their associated line cards. Group table  108 ′ includes a primary line card LID field  447  and a backup line card LID field  449  such that, in addition to starting primary instances of ATM, each primary line card also executes backup instances of ATM. For example, ATM controller  136   a  receives records  450 – 453  and  458 – 461  from group table  108 ′ including LID  30  (line card  16   a ). Records  450 – 453  indicate that ATM controller  136   a  is to start four primary instantiations of ATM  464 – 467  ( FIG. 29 ), and records  458 – 461  indicate that ATM controller  136   a  is to start four backup instantiations of ATM  468 – 471  as backup for four primary instantiations on LID  32  (line card  16   c ). Similarly, ATM controller  136   b  receives records  450 – 457  from group table  108 ′ including LID  31  (line card  16   b ). Records  454 – 457  indicate that ATM controller  136   b  is to start four primary instantiations of ATM  472 – 475 , and records  450 – 453  indicate that ATM controller  136   b  is to start four backup instantiations of ATM  476 – 479  as backup for four primary instantiations on LID  30  (line card  16   a ). ATM controller  136   c  receives records  454 – 461  from group table  108 ′ including LID  32  (line card  16   c ). Records  458 – 461  indicate that ATM controller  136   c  is to start four primary instantiations of ATM  480 – 483 , and records  454 – 457  indicate that ATM controller  136   c  is to start four backup instantiations of ATM  484 – 487  as backup for four primary instantiations on LID  31  (line card  16   b ). ATM controllers  136   a,    136   b  and  136   c  then download atm.exe  138  and generate the appropriate number of ATM instantiations and also indicate to each instantiation whether it is a primary or backup instantiation. Alternatively, the ATM controllers may download atm.exe and generate the appropriate number of primary ATM instantiations and download a separate backup_atm.exe and generate the appropriate number of backup ATM instantiations. 
   Each primary instantiation registers with its local name server  220   b – 220   d,  as described above, and each backup instantiation subscribes to its local name server  220   b – 220   d  for information about its corresponding primary instantiation. The name server passes each backup instantiation at least the process identification number assigned to its corresponding primary instantiation, and with this, the backup instantiation sends a message to the primary instantiation to set up a dynamic state check-pointing procedure. Periodically or asynchronously as state changes, the primary instantiation passes dynamic state information to the backup instantiation (i.e., check-pointing). In one embodiment, a Redundancy Manager Service available from Harris and Jefferies of Dedham, Mass. may be used to allow backup and primary instantiations to pass dynamic state information. If the primary instantiation fails, it can be re-started, retrieve its last known dynamic state from the backup instantiation and then initiate an audit procedure (as described above) to resynchronize with other processes. The retrieval and audit process will normally be completed very quickly, resulting in no discemable service disruption. 
   Although each line card in the example above is instructed by the group table to start four instantiations of ATM, this is by way of example only. The user could instruct the NMS to set up the group table to have each line card start one or more instantiations and to have each line card start a different number of instantiations. 
   Referring to  FIGS. 31   a – 31   c,  if one or more of the primary processes on element  16   a  (ATM  464 – 467 ) experiences a software fault ( FIG. 31   b ), the processor on line card  16   a  may terminate and restart the failing process or processes. Once the process or processes are restarted (ATM  464 ′– 467 ′,  FIG. 31   c ), they retrieve a copy of the last known dynamic state (i.e., backup state) from corresponding backup processes (ATM  476 – 479 ) executing on line card  16   b  and initiate an audit process to synchronize retrieved state with the dynamic state of associated other processes. The backup state represents the last known active or dynamic state of the process or processes prior to termination, and retrieving this state from line card  16   b  allows the restarted processes on line card  16   a  to quickly resynchronize and continue operating. The retrieval and audit process will normally be completed very quickly, and in the case of a network device, quick resynchronization may avoid losing network connections, resulting in no discemable service disruption. 
   If, instead of restarting a particular application, the software fault experienced by line card  16   a  requires the entire element to be shut down and rebooted, then all of the processes executing on line card  16   a  will be terminated including backup processes ATM  468 – 471 . When the primary processes are restarted, backup state information is retrieved from backup processes executing on line card  16   b  as explained above. Simultaneously, the restarted backup processes on line card  16   a  again initiate the check-pointing procedure with primary ATM processes  480 – 483  executing on line card  16   c  to again serve as backup processes for these primary processes. Referring to  FIGS. 32   a – 32   c,  the primary processes executing on one line card may be backed-up by backup processes running on one or more other line cards. In addition, each primary process may be backed-up by one or more backup processes executing on one or more of the other line cards. 
   Since the operating system assigns each process its own memory block, each primary process may be backed-up by a backup process running on the same line card. This would minimize the time required to retrieve backup state and resynchronize if a primary process fails and is restarted. In a computer system that includes a spare or backup line card (described below), the backup state is best saved on another line card such that in the event of a hardware fault, the backup state is not lost and can be copied from the other line card. If memory and processor limitations permit, backup processes may run simultaneously on the same line card as the primary process and on another line card such that software faults are recovered from using local backup state and hardware faults are recovered from using remote backup state. 
   Where limitations on processing power or memory make full hot state backup impossible or impractical, only certain hot state data will be stored as backup. The level of hot state backup is inversely proportional to the resynchronization time, that is, as the level of hot state backup increases, resynchronization time decreases. For a network device, backup state may include critical information that allows the primary process to quickly re-synchronize. 
   Critical information for a network device may include connection data relevant to established network connections (e.g., call set up information and virtual circuit information). For example, after primary ATM applications  464 – 467 , executing on line card  16   a,  establish network connections, those applications send critical state information relevant to those connections to backup ATM applications  479 – 476  executing on line card  16   b.  Retrieving connection data allows the hardware (i.e., line card  16   a ) to send and receive network data over the previously established network connections preventing these connections from being terminated/dropped. 
   Although ATM applications were used in the examples above, this is by way of example only. Any application (e.g., IP or MPLS), process (e.g., MCD or NS) or device driver (e.g., port driver) may have a backup process started on another line card to store backup state through a check-pointing procedure. 
   Hardware and Software Backup: 
   By adding one or more hardware backup elements (e.g., line card  16   n ) to the computer system, the distributed redundancy architecture provides both hardware and software backup. Software backup may be spread across all of the line cards or only some of the line cards. For example, software backup may be spread only across the primary line cards, only on one or more backup line cards or on a combination of both primary and backup line cards. 
   Referring to  FIG. 33   a,  in the continuing example, line cards  16   a,    16   b  and  16   c  are primary hardware elements and line card  16   n  is a spare or backup hardware element. In this example, software backup is spread across only the primary line cards. Alternatively, backup line card  16   n  may also execute backup processes to provide software backup. Backup line card  16   n  may execute all backup processes such that the primary elements need not execute any backup processes or line card  16   n  may execute only some of the backup processes. Regardless of whether backup line card  16   n  executes any backup processes, it is preferred that line card  16   n  be at least partially operational and ready to use the backup processes to quickly begin performing as if it was a failed primary line card. 
   There are many levels at which a backup line card may be partially operational. For example, the backup line card&#39;s hardware may be configured and device driver processes  490  loaded and ready to execute. In addition, the active state of the device drivers  492 ,  494 , and  496  on each of the primary line cards may be stored as backup device driver state (DDS)  498 ,  500 ,  502  on backup line card  16   n  such that after a primary line card fails, the backup device driver state corresponding to that primary element is used by device driver processes  490  to quickly synchronize the hardware on backup line card  16   n.    
   In addition, data reflecting the network connections established by each primary process may be stored within each of the backup processes or independently on backup line card  16   n,  for example, connection data (CD)  504 ,  506 ,  508 . Having a copy of the connection data on the backup line card allows the hardware to quickly begin transmitting network data over previously established connections to avoid the loss of these connections and minimize service disruption. The more operational (i.e., hotter) backup line card  16   n  is the faster it will be able to transfer data over network connections previously established by the failed primary line card and resynchronize with the rest of the system. 
   In the case of a primary line card hardware fault, the backup or spare line card takes the place of the failed primary line card. The backup line card starts new primary processes that register with the name server on the backup line card and begin retrieving active state from backup processes associated with the original primary processes. As described above, the same may also be true for software faults. Referring to  FIG. 33   b,  if, for example, line card  16   a  in computer system  10  is affected by a fault, the slave SRM executing on backup line card  16   n  may start new primary processes  464 ′– 467 ′ corresponding to the original primary processes  464 – 467 . The new primary processes register with the name server process executing on line card  16   n  and begin retrieving active state from backup processes  476 – 479  on line card  16   b.  This is referred to as a “fail-over” from failed primary line card  16   a  to backup line card  16   n.    
   As discussed above, preferably, backup line card  16   n  is partially operational. While active state is being retrieved from backup processes on line card  16   b,  device driver processes  490  use device driver state  502  and connection data  508  corresponding to failed primary line card  16   a  to quickly continue passing network data over previously established connections. Once the active state is retrieved then the ATM applications resynchronize and may begin establishing new connections and tearing down old connections. 
   Floating Backup Element: 
   Referring to  FIG. 33   c,  when the fault is detected on line card  16   a,  diagnostic tests may be run to determine if the error was caused by software or hardware. If the fault is a software error, then line card  16   a  may again be used as a primary line card. If the fault is a hardware error, then line card  16   a  is replaced with a new line card  16   a ′ that is booted and configured and again ready to be used as a primary element. In one embodiment, once line card  16   a  or  16   a ′ is ready to serve as a primary element, a fail-over is initiated from line card  16   n  to line card  16   a  or  16   a ′ as described above, including starting new primary processes  464 ″– 467 ″ and retrieving active state from primary processes  464 ′– 467 ′ on line card  16   n  (or backup processes  476 – 479  on line card  16   b ). Backup processes  468 ″– 471 ″ are also started, and those backup processes initiate a check-pointing procedure with primary processes  480 – 483  on line card  16   c.  This fail-over may cause the same level of service interruption as an actual failure. 
   Instead of failing-over from line card  16   n  back to line card  16   a  or  16   a ′ and risking further service disruption, line card  16   a  or  16   a ′ may serve as the new backup line card with line card  16   n  serving as the primary line card. If line cards  16   b,    16   c  or  16   n  experience a fault, a fail-over to line card  16   a  is initiated as discussed above and the primary line card that failed (or a replacement of that line card) serves as the new backup line card. This is referred to as a “floating” backup element. Referring to  FIG. 33   d,  if, for example, line card  16   c  experiences a fault, primary processes  480 ′– 483 ′ are started on backup line card  16   a  and active state is retrieved from backup processes  464 ′– 467 ′ on line card  16   n.  After line card  16   c  is rebooted or replaced and rebooted, it serves as the new backup line card for primary line cards  16   a,    16   b  and  16   n.    
   Alternatively, computer system  10  may be physically configured to only allow a line card in a particular chassis slot, for example, line card  16   n,  to serve as the backup line card. This may be the case where physically, the slot line card  16   n  is inserted within is wired to provide the necessary connections to allow line card  16   n  to communicate with each of the other line cards but no other slot provides these connections. In addition, even where the computer system is capable of allowing line cards in other chassis slots to act as the backup line card, the person acting as network manager, may prefer to have the backup line card in each of his computer systems in the same slot. In either case, where only line card  16   n  serves as the backup line card, once line card  16   a  (or any other failed primary line card) is ready to act as a primary line card again, a fail-over, as described above, is initiated from line card  16   n  to the primary line card to allow line card  16   n  to again serve as a backup line card to each of the primary line cards. 
   Balancing Resources: 
   Typically, multiple processes or applications are executed on each primary line card. Referring to  FIG. 34   a,  in one embodiment, each primary line card  16   a,    16   b,    16   c  executes four applications. Due to physical limitations (e.g., memory space, processor power), each primary line card may not be capable of fully backing up four applications executing on another primary line card. The distributed redundancy architecture allows backup processes to be spread across multiple line cards, including any backup line cards, to more efficiently use all system resources. 
   For instance, primary line card  16   a  executes backup processes  510  and  512  corresponding to primary processes  474  and  475  executing on primary line card  16   b.  Primary line card  16   b  executes backup processes  514  and  516  corresponding to primary processes  482  and  483  executing on primary line card  16   c,  and primary line card  16   c  executes backup processes  518  and  520  corresponding to primary processes  466  and  467  executing on primary line card  16   a.  Backup line card  16   n  executes backup processes  520 ,  522 ,  524 ,  526 ,  528  and  530  corresponding to primary processes  464 ,  465 ,  472 ,  473 ,  480  and  481  executing on each of the primary line cards. Having each primary line card execute backup processes for only two primary processes executing on another primary line card reduces the primary line card resources required for backup. Since backup line card  16   n  is not executing primary processes, more resources are available for backup. Hence, backup line card  16   n  executes six backup processes corresponding to six primary processes executing on primary line cards. In addition, backup line card  16   n  is partially operational and is executing device driver processes  490  and storing device driver backup state  498 ,  500  and  502  corresponding to the device drivers on each of the primary elements and network connection data  504 ,  506  and  508  corresponding to the network connections established by each of the primary line cards. 
   Alternatively, each primary line card could execute more or less than two backup processes. Similarly, each primary line card could execute no backup processes and backup line card  16   n  could execute all backup processes. Many alternatives are possible and backup processes need not be spread evenly across all primary line cards or all primary line cards and the backup line card. 
   Referring to  FIG. 34   b,  if primary line card  16   b  experiences a failure, device drivers  490  on backup line card  16   n  begins using the device driver state, for example, DDS  498 , corresponding to the device drivers on primary line card  16   b  and the network connection data, for example, CD  506 , corresponding to the connections established by primary line card  16   b  to continue transferring network data. Simultaneously, backup line card  16   n  starts substitute primary processes  510 ′ and  512 ′ corresponding to the primary processes  474  and  475  on failed primary line card  16   b.  Substitute primary processes  510 ′ and  512 ′ retrieve active state from backup processes  510  and  512  executing on primary line card  16   a.  In addition, the slave SRM on backup line card  16   n  informs backup processes  526  and  524  corresponding to primary processes  472  and  473  on failed primary line card  16   b  that they are now primary processes. The new primary applications then synchronize with the rest of the system such that new network connections may be established and old network connections torn down. That is, backup line card  16   n  begins operating as if it were primary line card  16   b.    
   Multiple Backup Elements: 
   In the examples given above, one backup line card is shown. Alternatively, multiple backup line cards may be provided in a computer system. In one embodiment, a computer system includes multiple different primary line cards. For example, some primary line cards may support the Asynchronous Transfer Mode (ATM) protocol while others support the Multi-Protocol Label Switching (MPLS) protocol, and one backup line card may be provided for the ATM primary line cards and another backup line card may be provided for the MPLS primary line cards. As another example, some primary line cards may support four ports while others support eight ports and one backup line card may be provided for the four port primaries and another backup line card may be provided for the eight port primaries. One or more backup line cards may be provided for each different type of primary line card. 
   Data Plane: 
   Referring to  FIGS. 35   a – 35   b , a network device  540  includes a central processor  542 , a redundant central processor  543  and a Fast Ethernet control bus  544  similar to central processors  12  and  13  and Ethernet  32  discussed above with respect to computer system  10 . In addition, network device  540  includes forwarding cards (FC)  546   a – 546   e,    548   a – 548   e,    550   a – 550   e  and  552   a – 552   e  that are similar to line cards  16   a – 16   n  discussed above with respect to computer system  10 . Network device  540  also includes (and computer system  10  may also include) universal port (UP) cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,  and  560   a – 560   h,  cross-connection (XC) cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b,  and  568   a – 568   b , and switch fabric (SF) cards  570   a – 570   b.  In one embodiment, network device  540  includes four quadrants where each quadrant includes five forwarding cards (e.g.,  546   a – 546   e ), two cross connection cards (e.g.,  562   a – 562   b ) and eight universal port cards (e.g.,  554   a – 554   h ). Network device  540  is a distributed processing system. Each of the cards includes a processor and is connected to the Ethernet control bus. In addition, each of the cards are configured as described above with respect to line cards. 
   In one embodiment, the forwarding cards have a 1:4 hardware redundancy structure and distributed software redundancy as described above. For example, forwarding card  546   e  is the hardware backup for primary forwarding cards  546   a – 546   d  and each of the forwarding cards provide software backup. The cross-connection cards are 1:1 redundant. For example, cross-connection card  562   b  provides both hardware and software backup for cross-connection card  562   a.  Each port on the universal port cards may be 1:1, 1+1, 1:N redundant or not redundant at all depending upon the quality of service paid for by the customer associated with that port. For example, port cards  554   e – 554   h  may be the hardware and software backup cards for port cards  554   a – 554   d  in which case the port cards are 1:1 or 1+1 redundant. As another example, one or more ports on port card  554   a  may be backed-up by separate ports on one or more port cards (e.g., port cards  554   b  and  554   c ) such that each port is 1:1 or 1+1 redundant, one or more ports on port card  554   a  may not be backed-up at all (i.e., not redundant) and two or more ports on  554   a  may be backed-up by one port on another port card (e.g., port card  554   b ) such that those ports are 1:N redundant. Many redundancy structures are possible using the LID to PID Card table (LPCT)  100  ( FIG. 14   b ) and LID to PID Port table (LPPT) as described above. 
   Each port card includes one or more ports for connecting to external network connections. One type of network connection is an optical fiber carrying an OC-48 SONET stream, and as described above, an OC-48 SONET stream may include connections to one or more end points using one or more paths. A SONET fiber carries a time division multiplexed (TDM) byte stream of aggregated time slots (TS). A time slot has a bandwidth of 51 Mbps and is the fundamental unit of bandwidth for SONET. An STS-1 path has one time slot within the byte stream dedicated to it, while an STS-3c path (i.e., three concatenated STS-1s) has three time slots within the byte stream dedicated to it. The same or different protocols may be carried over different paths within the same TDM byte stream. In other words, ATM over SONET may be carried on an STS-1 path within a TDM byte stream that also includes IP over SONET on another STS-1 path or on an STS-3c path. 
   Through network management system  60  on workstation  62 , after a user connects an external network connection to a port, the user may enable that port and one or more paths within that port (described below). Data received on a port card path is passed to the cross-connection card in the same quadrant as the port card, and the cross-connection card passes the path data to one of the five forwarding cards or eight port cards also within the same quadrant. The forwarding card determines whether the payload (e.g., packets, frames or cells) it is receiving includes user payload data or network control information. The forwarding card itself processes certain network control information and sends certain other network control information to the central processor over the Fast Ethernet control bus. The forwarding card also generates network control payloads and receives network control payloads from the central processor. The forwarding card sends any user data payloads from the cross-connection card or control information from itself or the central processor as path data to the switch fabric card. The switch fabric card then passes the path data to one of the forwarding cards in any quadrant, including the forwarding card that just sent the data to the switch fabric card. That forwarding card then sends the path data to the cross-connection card within its quadrant, which passes the path data to one of the port cards within its quadrant. 
   Referring to  FIGS. 36   a – 36   b , in one embodiment, a universal port card  554   a  includes one or more ports  571   a – 571   n  connected to one or more transceivers  572   a – 572   n.  The user may connect an external network connection to each port. As one example, port  571   a  is connected to an ingress optical fiber  576   a  carrying an OC-48 SONET stream and an egress optical fiber  576   b  carrying an OC-48 SONET stream. Port  571   a  passes optical data from the SONET stream on fiber  576   a  to transceiver  572   a.  Transceiver  572   a  converts the optical data into electrical signals that it sends to a SONET framer  574   a.  The SONET framer organizes the data it receives from the transceiver into SONET frames. SONET framer  574   a  sends data over a telecommunications bus  578   a  to a serializer-deserializer (SERDES)  580   a  that serializes the data into four serial lines with twelve STS-1 time slots each and transmits the four serial lines to cross-connect card  562   a.    
   Each cross-connection card is a switch that provides connections between port cards and forwarding cards within its quadrant. Each cross-connection card is programmed to transfer each serial line on each port card within its quadrant to a forwarding card within its quadrant or to serial line on a port card, including the port card that transmitted the data to the cross-connection card. The programming of the cross-connect card is discussed in more detail below under Policy Based Provisioning. 
   Each forwarding card (e.g., forwarding card  546   c ) receives SONET frames over serial lines from the cross-connection card in its quadrant through a payload extractor chip (e.g., payload extractor  582   a ). In one embodiment, each forwarding card includes four payload extractor chips where each payload extractor chip represents a “slice” and each serial line input represents a forwarding card “port”. Each payload extractor chip receives four serial line inputs, and since each serial line includes twelve STS-1 time slots, the payload extractor chips combine and separate time slots where necessary to output data paths with the appropriate number of time slots. Each STS-1 time slot may represent a separate data path, or multiple STS-1 time slots may need to be combined to form a data path. For example, an STS-3c path requires the combination of three STS-1 time slots to form a data path while an STS- 48   c  path requires the combination of all forty-eight STS-1 time slots. Each path represents a separate network connection, for example, an ATM cell stream. 
   The payload extractor chip also strips off all vestigial SONET frame information and transfers the data path to an ingress interface chip. The ingress interface chip will be specific to the protocol of the data within the path. As one example, the data may be formatted in accordance with the ATM protocol and the ingress interface chip is an ATM interface chip (e.g., ATM IF  584   a ). Other protocols can also be implemented including, for example, Internet Protocol (IP), Multi-Protocol Label Switching (MPLS) protocol or Frame Relay. 
   The ingress ATM IF chip performs many functions including determining connection information (e.g., virtual circuit or virtual path information) from the ATM header in the payload. The ATM IF chip uses the connection information as well as a forwarding table to perform an address translation from the external address to an internal address. The ATM IF chip passes ATM cells to an ingress bridge chip (e.g., BG  586   a – 586   b ) which serves as an interface to an ingress traffic management chip or chip set (e.g., TM  588   a – 588   n ). 
   The traffic management chips ensure that high priority traffic, for example, voice data, is passed to switch fabric card  570   a  faster than lower priority traffic, for example, e-mail data. The traffic management chips may buffer lower priority traffic while higher priority traffic is transmitted, and in times of traffic congestion, the traffic management chips will ensure that low priority traffic is dropped prior to any high priority traffic. The traffic management chips also perform an address translation to add the address of the traffic management chip to which the data is going to be sent by the switch fabric card. The address corresponds to internal virtual circuits set up between forwarding cards by the software and available to the traffic management chips in tables. 
   The traffic management chips send the modified ATM cells to switch fabric interface chips (SFIF)  589   a – 589   n  that then transfer the ATM cells to switch fabric card  570   a.  The switch fabric card uses the address provided by the ingress traffic management chips to pass ATM cells to the appropriate egress traffic management chips (e.g., TM  590   a – 590   n ) on the various forwarding cards. In one embodiment, the switch fabric card  570   a  is a 320 Gbps, non-blocking fabric. Since each forwarding card serves as both an ingress and egress, the switching fabric card provides a high degree of flexibility in directing the data between any of the forwarding cards, including the forwarding card that sent the data to the switch fabric card. 
   When a forwarding card (e.g., forwarding card  546   c ) receives ATM cells from switch fabric card  570   a,  the egress traffic management chips re-translate the address of each cell and pass the cells to egress bridge chips (e.g., BG  592   a – 592   b ). The bridge chips pass the cells to egress ATM interface chips (e.g., ATM IF  594   a – 594   n ), and the ATM interface chips add a re-translated address to the payload representing an ATM virtual circuit. The ATM interface chips then send the data to the payload extractor chips (e.g., payload extractor  582   a – 582   n ) that separate, where necessary, the path data into STS-1 time slots and combine twelve STS-1 time slots into four serial lines and send the serial lines back through the cross-connection card to the appropriate port card. 
   The port card SERDES chips receive the serial lines from the cross-connection card and de-serialize the data and send it to SONET framer chips  574   a – 574   n.  The Framers properly format the SONET overhead and send the data back through the transceivers that change the data from electrical to optical before sending it to the appropriate port and SONET fiber. 
   Although the port card ports above were described as connected to a SONET fiber carrying an OC-48 stream, other SONET fibers carrying other streams (e.g., OC-12) and other types of fibers and cables, for example, Ethernet, may be used instead. The transceivers are standard parts available from many companies, including Hewlett Packard Company and Sumitomo Corporation. The SONET framer may be a Spectra chip available from PMC-Sierra, Inc. in British Columbia. A Spectra 2488 has a maximum bandwidth of 2488 Mbps and may be coupled with a 1xOC48 transceiver coupled with a port connected to a SONET optical fiber carrying an OC-48 stream also having a maximum bandwidth of 2488 Mbps. Instead, four SONET optical fibers carrying OC-12 streams each having a maximum bandwidth of 622 Mbps may be connected to four 1xOC12 transceivers and coupled with one Spectra 2488. Alternatively, a Spectra 4x155 may be coupled with four OC-3 transceivers that are coupled with ports connected to four SONET fibers carrying OC-3 streams each having a maximum bandwidth of 155 Mbps. Many variables are possible. 
   The SERDES chip may be a Telecommunications Bus Serializer (TBS) chip from PMC-Sierra, and each cross-connection card may include a Time Switch Element (TSE) from PMC-Sierra, Inc. Similarly, the payload extractor chips may be MACH 48 chips and the ATM interface chips may be ATLAS chips both of which are available from PMC-Sierra. Several chips are available from Extreme Packet Devices (EPD), a subsidiary of PMC-Sierra, including PP3 bridge chips and Data Path Element (DPE) traffic management chips. The switch fabric interface chips may include a Switch Fabric Interface (SIF) chip also from EPD. Other switch fabric interface chips are available from Abrizio, also a subsidiary of PMC-Sierra, including a data slice chip and an enhanced port processor (EPP) chip. The switch fabric card may also include chips from Abrizio, including a cross-bar chip and a scheduler chip. 
   Although the port cards, cross-connection cards and forwarding cards have been shown as separate cards, this is by way of example only and they may be combined into one or more different cards. 
   Multiple Redundancy Schemes: 
   Coupling universal port cards to forwarding cards through a cross-connection card provides flexibility in data transmission by allowing data to be transmitted from any path on any port to any port on any forwarding card. In addition, decoupling the universal port cards and the forwarding cards enables redundancy schemes (e.g., 1:1, 1+1, 1:N, no redundancy) to be set up separately for the forwarding cards and universal port cards. The same redundancy scheme may be set up for both or they may be different. As described above, the LID to PID card and port tables are used to setup the various redundancy schemes for the line cards (forwarding or universal port cards) and ports. Network devices often implement industry standard redundancy schemes, such as those defined by the Automatic Protection Switching (APS) standard. In network device  540  ( FIGS. 35   a – 35   b ), an APS standard redundancy scheme may be implemented for the universal port cards while another redundancy scheme is implemented for the forwarding cards. 
   Referring again to  FIGS. 35   a – 35   b , further data transmission flexibility may be provided by connecting (i.e., connections  565 ) each cross-connection card  562   a – 562   b,    564   a – 564   b,    566   a – 566   b  and  568   a – 568   b  to each of the other cross-connection cards. Through connections  565 , a cross-connection card (e.g., cross-connection card  562   a ) may transmit data between any port or any path on any port on a universal port card (e.g., universal port cards  554   a – 554   h ) in its quadrant to a cross-connection card (e.g., cross-connection card  568   a ) in any other quadrant, and that cross-connection card (e.g., cross-connection card  568   a ) may transmit the data to any forwarding card (e.g., forwarding cards  552   a – 552   e ) or universal port card (e.g., universal port cards  560   a – 560   h ) in its quadrant. Similarly, any cross-connection card may transmit data received from any forwarding card in its quadrant to any other cross-connection card and that cross-connection card may transmit the data to any universal port card port in its quadrant. 
   Alternatively, the cross-connection cards in each quadrant may be coupled only with cross-connection cards in one other quadrant. For example, cross-connection cards in quadrants  1  and  2  may be connected and cross-connection cards in quadrants  3  and  4  may be connected. Similarly, the cross-connection cards in each quadrant may be coupled with cross-connection cards in only two other quadrants, or only the cross-connection cards in one quadrant (e.g., quadrant  1 ) may be connected to cross-connection cards in another quadrant (e.g., quadrant  2 ) while the cross-connection cards in the other quadrants (e.g., quadrants  3  and  4 ) are not connected to other cross-connection cards or are connected only to cross-connection cards in one quadrant (e.g., quadrant  2 ). Many variations are possible. Although these connections do not provide the flexibility of having all cross-connection cards inter-connected, these connections require less routing resources and still provide some increase in the data transmission flexibility of the network device. 
   The additional flexibility provided by inter-connecting one or more cross-connection cards may be used to optimize the efficiency of network device  540 . For instance, a redundant forwarding card in one quadrant may be used as a backup for primary forwarding cards in other quadrants thereby reducing the number of backup modules and increasing the network device&#39;s service density. Similarly, a redundant universal port card or a redundant port on a universal port card in one quadrant may be used as a backup for primary universal port cards or ports in other quadrants. As previously mentioned, each primary forwarding card may support a different protocol (e.g., ATM, MPLS, IP, Frame Relay). Similarly, each universal port card may support a different protocol (e.g., SONET, Ethernet). A backup or spare forwarding card or universal port card must support the same protocol as the primary card or cards. If forwarding or universal port cards in one quadrant support multiple protocols and the cross-connection cards are not interconnected, then each quadrant may need multiple backup forwarding and universal port cards (i.e., one for each protocol supported). If each of the quadrants includes forwarding and universal port cards that support different protocols then each quadrant may include multiple backup forwarding and universal port cards further decreasing the network device&#39;s service density. 
   By inter-connecting the cross-connection cards, a forwarding card in one quadrant may serve as a backup for primary forwarding cards in its own quadrant and in other quadrants. Similarly, a universal port card or port in one quadrant may serve as a backup for a primary universal port card or port in its own quadrant and in other quadrants. For example, forwarding card  546   e  in quadrant  1  that supports a particular protocol (e.g., the ATM protocol) may serve as the backup forwarding card for primary forwarding cards supporting ATM in its own quadrant (e.g., forwarding cards  546   a – 546   b ) as well as for primary forwarding cards supporting ATM in quadrant  2  (e.g., forwarding cards  548   b – 548   c ) or all quadrants (e.g., forwarding card  550   c  in quadrant  3  and forwarding cards  552   b – 552   d  in quadrant  4 ). Similarly, forwarding card  548   e  in quadrant  2  that supports a different protocol (e.g., the MPLS protocol) may serve as the backup forwarding card for primary forwarding cards supporting MPLS in its own quadrant (e.g., forwarding cards  548   a  and  548   d ) as well as for primary forwarding cards supporting MPLS in quadrant  1  (e.g., forwarding card  546   c ) or all quadrants (e.g., forwarding card  550   a  in quadrant  3  and forwarding card  552   a  in quadrant  4 ). Even with this flexibility, to provide sufficient redundancy, multiple backup modules supporting the same protocol may be used, especially where a large number of primary modules support one protocol. 
   As previously discussed, each port on a universal port card may be connected to an external network connection, for example, an optical fiber transmitting data according to the SONET protocol. Each external network connection may provide multiple streams or paths and each stream or path may include data being transmitted according to a different protocol over SONET. For example, one path may include data being transmitted according to ATM over SONET while another path may include data being transmitted according to MPLS over SONET. The cross-connection cards may be programmed (as described below) to transmit protocol specific data (e.g., ATM, MPLS, IP, Frame Relay) from ports on universal port cards within their quadrants to forwarding cards within any quadrant that support the specific protocol. Because the traffic management chips on the forwarding cards provide protocol-independent addresses to be used by switch fabric cards  570   a – 570   b,  the switch fabric cards may transmit data between any of the forwarding cards regardless of the underlying protocol. 
   Alternatively, the network manager may dedicate each quadrant to a specific protocol by putting forwarding cards in each quadrant according to the protocol they support. Within each quadrant then, one forwarding card may be a backup card for each of the other forwarding cards (1:N, for network device  540 , 1:4). Protocol specific data received from ports or paths on ports on universal port cards within any quadrant may then be forwarded by one or more cross-connection cards to forwarding cards within the protocol specific quadrant. For instance, quadrant  1  may include forwarding cards for processing data transmissions using the ATM protocol, quadrant  2  may include forwarding cards for processing data transmissions using the IP protocol, quadrant  3  may include forwarding cards for processing data transmissions using the MPLS protocol and quadrant  4  may be used for processing data transmissions using the Frame Relay protocol. ATM data received on a port path is then transmitted by one or more cross-connection cards to a forwarding card in quadrant  1 , while MPLS data received on another path on that same port or on a path in another port is transmitted by one or more cross-connection cards to a forwarding card in quadrant  3 . 
   Policy Based Provisioning: 
   Unlike the switch fabric card, the cross-connection card does not examine header information in a payload to determine where to send the data. Instead, the cross-connection card is programmed to transmit payloads, for example, SONET frames, between a particular serial line on a universal port card port and a particular serial line on a forwarding card port regardless of the information in the payload. As a result, one port card serial line and one forwarding card serial line will transmit data to each other through the cross-connection card until that programmed connection is changed. 
   In one embodiment, connections established through a path table and service endpoint table (SET) in a configuration database are passed to path managers on port cards and service endpoint managers (SEMs) on forwarding cards, respectively. The path managers and service endpoint managers then communicate with a cross-connect manager (CCM) on the cross-connection card in their quadrant to provide connection information. The CCM uses the connection information to generate a connection program table that is used by one or more components (e.g., a TSE chip  563 ) to program internal connection paths through the cross-connection card. 
   Typically, connections are fixed or are generated according to a predetermined map with a fixed set of rules. Unfortunately, a fixed set of rules may not provide flexibility for future network device changes or the different needs of different users/customers. Instead, within network device  540 , each time a user wishes to enable/configure a path on a port on a universal port card, a Policy Provisioning Manager (PPM)  599  ( FIG. 37 ) executing on central processor  542  selects the forwarding card port to which the port card port will be connected based on a configurable provisioning policy (PP)  603  in configuration database  42 . The configurable provisioning policy may take into consideration many factors such as available system resources, balancing those resources and quality of service. Similar to other programs and files stored within the configuration database of computer system  10  described above, the provisioning policy may be modified while network device  540  is running to allow to policy to be changed according to a user&#39;s changing needs or changing network device system requirements. 
   When a user connects an external network connection to a particular port on a universal port card, the user notifies the NMS as to which port on which universal port card should be enabled, which path or paths should be enabled, and the number of time slots in each path. The user may also notify the NMS as to a new path and its number of time slots on an already enabled port that was not fully utilized or the user may notify the NMS of a modification to one or more paths on already enabled ports and the number of time slots required for that path or paths. With this information, the NMS fills in a Path table  600  ( FIGS. 37 and 38 ) and partially fills in a Service Endpoint Table (SET)  76 ′ ( FIGS. 37 and 39 ). 
   When a record in the path table is filled in, the configuration database sends an active query notification to a path manager (e.g., path manager  597 ) executing on a universal port card (e.g., port card  554   a ) corresponding to the universal port card port LID (e.g., port  1231 ,  FIG. 38 ) in the path table record (e.g., record  602 ). 
   Leaving some fields in the SET blank or assigning a particular value (e.g., zero), causes the configuration database to send an active query notification to Policy Provisioning Manager (PPM)  599 . The PPM then determines—using provisioning policy  603 —which forwarding card (FC) port or ports to assign to the new path or paths. For example, the PPM may first compare the new path&#39;s requirements, including its protocol (e.g., ATM over SONET), the number of time slots, the number of virtual circuits and virtual circuit scheduling restrictions, to the available forwarding card resources in the quadrant containing the universal port card port and path. The PPM also takes other factors into consideration including quality of service, for example, redundancy requirements or dedicated resource requirements, and balancing resource usage (i.e., load balancing) evenly within a quadrant. 
   As an example, a user connects SONET optical fiber  576   a  ( FIGS. 36   a – 36   b ) to port  571   a  on universal port card  554   a  and wants to enable a path with three time slots (i.e., STS-3c). The NMS assigns a path LID number (e.g., path LID  1666 ) and fills in a record (e.g., row  602 ) in Path Table  600  to include path LID  1666 , a universal port card port LID (e.g., UP port LID  1231 ) previously assigned by the NMS and retrieved from the Logical to Physical Port Table, the first time slot (e.g., time slot  4 ) in the SONET stream corresponding with the path and the total number of time slots—in this example, 3—in the path. Other information may also be filled into Path Table  600 . 
   The NMS also partially fills in a record (e.g., row  604 ) in SET  76 ′ by filling in the quadrant number—in this example, 1—and the assigned path LID  1666  and by assigning a service endpoint number  878 . The SET table also includes other fields, for example, a forwarding card LID field  606 , a forwarding card slice  608  (i.e., port) and a forwarding card serial line  610 . In one embodiment, the NMS fills in these fields with a particular value (e.g., zero), and in another embodiment, the NMS leaves these fields blank. 
   In either case, the particular value or a blank field causes the configuration database to send an active query notice to the PPM indicating a new path LID, quadrant number and service endpoint number. It is up to the PPM to decide which forwarding card, slice (i.e., payload extractor chip) and time slot (i.e., port) to assign to the new universal port card path. Once decided, the PPM fills in the SET Table fields. Since the user and NMS do not completely fill in the SET record, this may be referred to as a “self-completing configuration record.” Self-completing configuration records reduce the administrative workload of provisioning a network. 
   The SET and path table records may be automatically copied to persistent storage  21  to insure that if network device  540  is re-booted these configuration records are maintained. If the network device shuts down prior to the PPM filling in the SET record fields and having those fields saved in persistent storage, when the network device is rebooted, the SET will still include blank fields or fields with particular values which will cause the configuration database to again send an active query to the PPM. 
   When the forwarding card LID (e.g.,  1667 ) corresponding, for example, to forwarding card  546   c,  is filled into the SET table, the configuration database sends an active query notification to an SEM (e.g., SEM  96   i ) executing on that forwarding card and corresponding to the assigned slice and/or time slots. The active query notifies the SEM of the newly assigned service endpoint number (e.g., SE  878 ) and the forwarding card slice (e.g., payload extractor  582   a ) and time slots (i.e., 3 time slots from one of the serial line inputs to payload extractor  582   a ) dedicated to the new path. 
   Path manager  597  and SEM  96   i  both send connection information to a cross-connection manager  605  executing on cross-connection card  562   a —the cross-connection card within their quadrant. The CCM uses the connection information to generate a connection program table  601  and uses this table to program internal connections through one or more components (e.g., a TSE chip  563 ) on the cross-connection card. Once programmed, cross-connection card  562   a  transmits data between new path LID  1666  on SONET fiber  576   a  connected to port  571   a  on universal port card  554   a  and the serial line input to payload extractor  582   a  on forwarding card  546   c.    
   An active query notification is also sent to NMS database  61 , and the NMS then displays the new system configuration to the user. 
   Alternatively, the user may choose which forwarding card to assign to the new path and notify the NMS. The NMS would then fill in the forwarding card LID in the SET, and the PPM would only determine which time slots and slice within the forwarding card to assign. 
   In the description above, when the PPM is notified of a new path, it compares the requirements of the new path to the available/unused forwarding card resources. If the necessary resources are not available, the PPM may signal an error. Alternatively, the PPM could move existing forwarding card resources to make the necessary forwarding card resources available for the new path. For example, if no payload extractor chip is completely available in the entire quadrant, one path requiring only one time slot is assigned to payload extractor chip  582   a  and a new path requires forty-eight time slots, the one path assigned to payload extractor chip  582   a  may be moved to another payload extractor chip, for example, payload extractor chip  582   b  that has at least one time slot available and the new path may be assigned all of the time slots on payload extractor chip  582   a.  Moving the existing path is accomplished by having the PPM modify an existing SET record. The new path is configured as described above. 
   Moving existing paths may result in some service disruption. To avoid this, the provisioning policy may include certain guidelines to hypothesize about future growth. For example, the policy may require small paths—for example, three or less time slots—to be assigned to payload extractor chips that already have some paths assigned instead of to completely unassigned payload extractor chips to provide a higher likelihood that forwarding card resources will be available for large paths—for example, sixteen or more time slots—added in the future. 
   Multi-Layer Network Device in One Telco Rack: 
   Referring again to  FIGS. 35   a – 35   b , in one embodiment, each universal port card includes four ports, each of which is capable of being connected to an OC-48 SONET fiber. Since an OC-48 SONET fiber is capable of transferring data at 2.5 Giga bits per second (Gbps), each universal port card is capable of transferring data at 10 Gbps (4×2.5=10). With eight port cards per quadrant, the cross-connection card must be capable of transferring data at 80 Gbps. Typically, however, the eight port cards will be 1:1 redundant and only transfer 40 Gbps. In one embodiment, each forwarding card is capable of transferring 10 Gbps, and with five forwarding cards per quadrant, the switch fabric cards must be capable of transferring data at 200 Gbps. Typically, however, the five forwarding cards will be 1:N redundant and only transfer data at 40 Gbps. With four quadrants and full redundancy (1:1 for port cards and 1:N for forwarding cards), network device  540  is capable of transferring data at 160 Gbps. 
   In other embodiments, each port card includes one port capable of being connected to an OC-192 SONET fiber. Since OC-192 SONET fibers are capable of transferring data at 10 Gbps, a fully redundant network device  540  is again capable of transferring 160 Gbps. In the embodiment employing one OC-192 connection per port card, each port card may include one hundred and ninety-two logical DS3 connections using sub-rate data multiplexing (SDRM). In addition, each port card may differ in its number and type of ports to provide more or less data through put. As previously mentioned, ports other than SONET ports may be provided, for example, Ethernet ports, Plesiochronous Digital Hierarchy ports (i.e., DS0, DS1, DS3, E0, E1, E3, J0, J1, J3) and Synchronous Digital Hierarchy (SDH) ports (i.e., STM1, STM4, STM16, STM64). 
   The universal port cards and cross-connect cards in each quadrant are in effect a physical layer switch, and the forwarding cards and switch fabric cards are effectively an upper layer switch. Prior systems have packaged these two switches into separate network devices. One reason for this is the large number of signals that need to be routed. Taken separately, each cross-connect card  562   a – 562   b,    564   a – 564   b,    566   a – 566   b  and  568   a – 568   b  is essentially a switch fabric or mesh allowing switching between any path on any universal port card to any serial input line on any forwarding card in its quadrant and each switch fabric card  570   a – 570   b  allows switching between any paths on any forwarding cards. Approximately six thousand, seven hundred and twenty etches are required to support a 200 Gbps switch fabric, and about eight hundred and thirty-two etches are required to support an 80 Gbps cross-connect. Combining such high capacity multi-layer switches into one network device in a single telco rack (seven feet by nineteen inches by 24 inches) has not been thought possible by those skilled in the art of telecommunications network devices. 
   To fit network device  540  into a single telco rack, dual mid-planes are used. All of the functional printed circuit boards connect to at least one of the mid-planes, and the switch A fabric cards and certain control cards connect to both mid-planes thereby providing connections between the two mid-planes. In addition, to efficiently utilize routing resources, instead of providing a single cross-connection card, the cross-connection functionality is separated into four cross-connection cards—one for each quadrant—(as shown in  FIGS. 35   a – 35   b ). Further, routing through the lower mid-plane is improved by flipping the forwarding cards and cross-connection cards in the bottom half of the front of the chassis upside down to be the mirror image of the forwarding cards and cross-connection cards in the top of the front half of the chassis. 
   Referring to  FIG. 40 , a network device  540  is packaged in a box  619  conforming to the telco standard rack of seven feet in height, nineteen inches in width and 24 inches in depth. Referring also to  FIGS. 41   a – 41   c,  a chassis  620  within box  619  provides support for forwarding cards  546   a – 546   e,    548   a – 548   e,    550   a – 550   e  and  552   a – 552   e,  universal port cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h  and  560   a – 560   h,  and cross-connection cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b  and  568   a – 568   b.  As is typical of telco network devices, the forwarding cards (FC) are located in the front portion of the chassis where network administrators may easily add and remove these cards from the box, and the universal port cards (UP) are located in the back portion of the chassis where external network attachments/cables may be easily connected. 
   The chassis also supports switch fabric cards  570   a  and  570   b.  As shown, each switch fabric card may include multiple switch fabric (SF) cards and a switch scheduler (SS) card. In addition, the chassis supports multiple central processor cards ( 542  and  543 ,  FIGS. 35   a – 35   b ). Instead of having a single central processor card, the external control functions and the internal control functions may be separated onto different cards as described in U.S. patent application Ser. No. 09/574,343, filed May 20, 2000 and entitled “Functional Separation of Internal and External Controls in Network Devices”, which is hereby incorporated herein by reference. As shown, the chassis may support internal control (IC) processor cards  542   a  and  543   a  and external control (EC) processor cards  542   b  and  543   b.  Auxiliary processor (AP) cards  542   c  and  543   c  are provided for future expansion to allow more external control cards to be added, for example, to handle new upper layer protocols. In addition, a management interface (MI) card  621  for connecting to an external network management system ( 62 ,  FIGS. 35   a – 35   b ) is also provided. 
   The chassis also support two mid-plane printed circuit boards  622   a  and  622   b  ( FIG. 41   c ) located toward the middle of chassis  620 . Mid-plane  622   a  is located in the top portion of chassis  620  and is connected to quadrant  1  and  2  forwarding cards  546   a – 546   e  and  548   a – 548   e,  universal port cards  554   a – 554   h  and  556   a – 556   h,  and cross-connection cards  562   a – 562   b  and  564   a – 564   b.  Similarly, mid-plane  622   b  is located in the bottom portion of chassis  620  and is connected to quadrant  3  and  4  forwarding cards  550   a – 550   e  and  552   a – 552   e,  universal port cards  558   a – 558   h  and  560   a – 560   h,  and cross-connection cards  566   a – 566   b  and  568   a – 568   b.  Through each mid-plane, the cross-connection card in each quadrant may transfer network packets between any of the universal port cards in its quadrant and any of the forwarding cards in its quadrant. In addition, through mid-plane  622   a  the cross-connection cards in quadrants  1  and  2  may be connected to allow for transfer of network packets between any forwarding cards and port cards in quadrants  1  and  2 , and through mid-plane  622   b  the cross-connection cards in quadrants  3  and  4  may be connected to allow for transfer of network packets between any forwarding cards and port cards in quadrants  3  and  4 . 
   Mid-plane  622   a  is also connected to external control processor cards  542   b  and  543   b  and management interface card  621 . Mid-plane  622   b  is also connected to auxiliary processor cards  542   c  and  543   c.    
   Switch fabric cards  570   a  and  570   b  are located in the back portion of chassis  620 , approximately mid-way between the top and bottom of the chassis. The switch fabric cards are connected to both mid-planes  622   a  and  622   b  to allow the switch fabric cards to transfer signals between any of the forwarding cards in any quadrant. In addition, the cross-connection cards in quadrants  1  and  2  may be connected through the mid-planes and switch fabric cards to the cross-connection cards in quadrants  3  and  4  to enable network packets to be transferred between any universal port card and any forwarding card. 
   To provide for better routing efficiency through mid-plane  622   b,  forwarding cards  550   a – 550   e  and  552   a – 552   e  and cross-connection cards  566   a – 566   b  and  568   a – 568   b  in quadrants  3  and  4 , located in the bottom portion of the chassis, are flipped over when plugged into mid-plane  622   b.  This permits the switch fabric interface  589   a – 589   n  on each of the lower forwarding cards to be oriented nearest the switch fabric cards and the cross-connection interface  582   a – 582   n  on each of the lower forwarding cards to be oriented nearest the cross-connection cards in quadrants  3  and  4 . This orientation avoids having to cross switch fabric and cross-connection etches in mid-plane  622   b.    
   Typically, airflow for cooling a network device is brought in at the bottom of the device and released at the top of the device. For example, in the back portion of chassis  620 , a fan tray (FT)  626  pulls air into the device from the bottom portion of the device and a fan tray  628  blows air out of the top portion of the device. When the lower forwarding cards are flipped over, the airflow/cooling pattern is reversed. To accommodate this reversal, fan trays  630  and  632  pull air into the middle portion of the device and then fan trays  634  and  636  pull the air upwards and downwards, respectively, and blow the heated air out the top and bottom of the device, respectively. 
   The quadrant  3  and  4  universal port cards  558   a – 558   h  and  560   a – 560   h  may also be flipped over to orient the port card&#39;s cross-connection interface nearest the cross-connection cards and more efficiently use the routing resources. It is preferred, however, not to flip the universal port cards for serviceability reasons and airflow issues. The network managers at the telco site expect network attachments/cables to be in a certain pattern. Reversing this pattern could cause confusion in a large telco site with many different types of network devices. Also, flipping the port cards will change the airflow and cooling pattern and require a similar airflow pattern and fan tray configuration as implemented in the front of the chassis. However, with the switch fabric and internal control processor cards in the middle of the back portion of the chassis, it may be impossible to implement this fan tray configuration. 
   Referring to  FIGS. 42   a – 42   b , mid-plane  622   a  includes connectors  638  mounted on the back side of the mid-plane (“back mounted”) for the management interface card, connectors  640   a – 640   d  mounted on the front side of the mid-plane (“front mounted”) for the quadrant  1  and  2  cross-connection cards, and front mounted connectors  642   a – 642   b  for the external control processor cards. Multiple connectors may be used for each card. Mid-plane  622   a  also includes back mounted connectors  644   a – 644   p  for the quadrant  1  and  2  universal port cards and front mounted connectors  646   a – 646   j  for the quadrant  1  and  2  forwarding cards. 
   Both mid-planes  622   a  and  622   b  include back mounted connectors  648   a – 648   d  for the switch fabric cards and back mounted connectors  650   a – 650   d  for the internal control cards. Mid-plane  622   b  further includes front, reverse mounted connectors  652   a – 652   j  for the quadrant  3  and  4  forwarding cards and back mounted connectors  654   a – 654   p  for the quadrant  3  and  4  universal port cards. In addition, mid-plane  622   b  also includes front, reverse mounted connectors  656   a – 656   d  for the quadrant  3  and  4  cross-connection cards and front mounted connectors  658   a – 658   b  for the auxiliary processor cards. 
   Combining both physical layer switch/router subsystems and upper layer switch/router subsystems in one network device allows for intelligent layer 1 switching. For example, the network device may be used to establish dynamic network connections on the layer 1 network to better utilize resources as service subscriptions change. In addition, network management is greatly simplified since the layer 1 and multiple upper layer networks may be managed by the same network management system and grooming fees are eliminated. Combining the physical layer switch/router and upper layer switch/routers into a network device that fits into one telco rack provides a less expensive network device and saves valuable telco site space. 
   Splitting the cross-connection function into four separate cards/quadrants enables the cross-connection routing requirements to be spread between the two mid-planes and alleviates the need to route cross-connection signals through the center of the device where the switch fabric is routed. In addition, segmenting the cross-connection function into multiple, independent subsystems allows customers/network managers to add functionality to network device  540  in pieces and in accordance with network service subscriptions. When a network device is first installed, a network manager may need only a few port cards and forwarding cards to service network customers. The modularity of network device  540  allows the network manager to purchase and install only one cross-connection card and the required number of port and forwarding cards. As the network becomes more subscribed, the network manager may add forwarding cards and port cards and eventually additional cross-connection cards. Since network devices are often very expensive, this modularity allows network managers to spread the cost of the system out in accordance with new service requests. The fees paid by customers to the network manager for the new services can then be applied to the cost of the new cards. 
   Although the embodiment describes the use of two mid-planes, it should be understood that more than two mid-planes may be used. Similarly, although the embodiment described flipped/reversed the forwarding cards and cross-connection cards in the lower half of the chassis, alternatively, the forwarding cards and cross-connection cards in the upper half of the chassis could be flipped. 
   Distributed Switch Fabric: 
   A network device having a distributed switch fabric locates a portion of the switch fabric functionality on cards separate from the remaining/central switch fabric functionality. For example, a portion of the switch fabric may be distributed on each forwarding card. There are a number of difficulties associated with distributing a portion of the switch fabric. For instance, distributing the switch fabric makes mid-plane/back-plane routing more difficult which further increases the difficulty of fitting the network device into one telco rack, switch fabric redundancy and timing are also made more difficult, valuable forwarding card space must be allocated for switch fabric components and the cost of each forwarding card is increased. However, since the entire switch fabric need not be included in a minimally configured network device, the cost of the minimal configuration is reduced allowing network service providers to more quickly recover the initial cost of the device. As new services are requested, additional functionality, including both forwarding cards (with additional switch fabric functionality) and universal port cards may be added to the network device to handle the new requests, and the fees for the new services may be applied to the cost of the additional functionality. Consequently, the cost of the network device more closely tracks the service fees received by network providers. 
   Referring again to  FIGS. 36   a – 36   b , as described above, each forwarding card (e.g.,  546   c ) includes traffic management chips (e.g.,  588   a – 588   n  and  590   a – 590   b ) that ensure high priority network data/traffic (e.g., voice) is transferred faster than lower priority traffic (e.g., e-mail). Each forwarding card also includes switch fabric interface (SFIF) chips (e.g.,  589   a – 589   n ) that transfer network data between the traffic management chips and the switch fabric cards  570   a – 570   b.    
   Referring also to  FIG. 43 , forwarding card  546   c  includes traffic management (TM) chips  588   n  and  590   a  and SFIF chips  589 , and forwarding card  550   a  includes traffic management chips  659   a  and  659   b  and SFIF chips  660 . ( FIG. 43  includes only two forwarding cards for convenience but it is to be understood that many forwarding cards may be included in a network device as shown in  FIGS. 35   a – 35   b .) SFIF chips  589  and  660  on both boards include a switch fabric interface (SIF) chip  661 , data slice chips  662   a – 662   f,  an enhanced port processor (EPP) chip  664  and a local timing subsystem (LTS)  665 . The SFIF chips receive data from ingress TM chips  588   n  and  659   a  and forward it to the switch fabric cards  570   a – 570   b  ( FIGS. 36   a – 36   b ). Similarly, the SFIF chips receive data from the switch fabric cards and forward it to the egress TM chips  590   a  and  659   b.    
   Due to the size and complexity of the switch fabric, each switch fabric card  570   a – 570   b  may include multiple separate cards. In one embodiment, each switch fabric card  570   a – 570   b  includes a control card  666  and four data cards  668   a – 668   d.  A scheduler chip  670  on control card  666  works with the EPP chips on each of the forwarding cards to transfer network data between the data slice chips on the forwarding cards through cross-bar chips  672   a – 6721  (only chips  672   a – 672   f  are shown) on data cards  668   a – 668   d.  Each of the data slice chips on each of the forwarding cards is connected to two of the cross-bar chips on the data cards. Switch fabric control card  666  and each of the switch fabric data cards  668   a – 668   d  also include a switch fabric local timing subsystem (LTS)  665 , and a switch fabric central timing subsystem (CTS)  673  on control card  666  provides a start of segment (SOS) reference signal to each LTS  665  on each of the forwarding cards and switch fabric cards. 
   The traffic management chips perform upper level network traffic management within the network device while scheduler chip  670  on control card  666  performs the lower level data transfer between forwarding cards. The traffic management chips determine the priority of received network data and then forward the highest priority data to SIF chips  661 . The traffic management chips include large buffers to store lower priority data until higher priority data has been transferred. The traffic management chips also store data in these buffers when the local EPP chip indicates that data transfers are to be stopped (i.e., back pressure). The scheduler chip works with the EPP chips to stop or hold-off data transfers when necessary, for example, when buffers on one forwarding card are close to full, the local EPP chip sends notice to each of the other EPP chips and the scheduler to hold off sending more data. Back pressure may be applied to all forwarding cards when a new switch fabric control card is added to the network device, as described below. 
   The traffic management chips forward network data in predefined segments to the SIF chips. In the case of ATM data, each ATM cell is a segment. In the case of IP and MPLS, where the amount of network data in each packet may vary, the data is first arranged into appropriately sized segments before being sent to the SIF chips. This may be accomplished through segmentation and reassembly (SAR) chips (not shown). 
   When the SIF chip receives a segment of network data, it organizes the data into a segment consistent with that expected by the switch fabric components, including any required header information. The SIF chip may be a PMC9324-TC chip available from Extreme Packet Devices (EPD), a subsidiary of PMC-Sierra, and the data slice chips may be PM9313-HC chips and the EPP chip may be a PM9315-HC chip available from Abrizio, also a subsidiary of PMC-Sierra. In this case, the SIF chip organizes each segment of data—including header information—in accordance with a line-card-to-switch two (LCS-2) protocol. The SIF chip then divides each data segment into twelve slices and sends two slices to each data slice chip  662   a – 662   f.  Two slices are sent because each data slice chip includes the functionality of two data slices. 
   When the data slice chips receive the LCS segments, the data slice chips strip off the header information, including both a destination address and quality of service (QoS) information, and send the header information to the local EPP chip. Alternatively, the SIF chip may send the header information directly to the EPP chip and send only data to the data slice chips. However, the manufacturer teaches that the SIF chip should be on the forwarding card and the EPP and data slice chips should be on a separate switch fabric card within the network device or in a separate box connected to the network device. Minimizing connections between cards is important, and where the EPP and data slice chips are not on the same card as the SIF chips, the header information is sent with the data by the SIF chip to reduce the required inter-card connections, and the data slice chips then strip off this information and send it to the EPP chip. 
   The EPP chips on all of the forwarding cards communicate and synchronize through cross-bar chips  674   a – 674   b  on control card  666 . For each time interval (e.g., every 40 nanoseconds, “ns”), the EPP chips inform the scheduler chip as to which data segment they would like to send and the data slice chips send a segment of data previously set up by the scheduler and EPP chips. The EPP chips and the scheduler use the destination addresses to determine if there are any conflicts, for example, to determine if two or more forwarding cards are trying to send data to the same forwarding card. If a conflict is found, then the quality of service information is used to determine which forwarding card is trying to send the higher priority data. The highest priority data will likely be sent first. However, the scheduler chips include an algorithm that takes into account both the quality of service and a need to keep the switch fabric data cards  668   a – 668   d  full (maximum data through put). Where a conflict exists, the scheduler chip may inform the EPP chip to send a different, for example, lower priority, data segment from the data slice chip buffers or to send an empty data segment during the time interval. 
   Scheduler chip  670  informs each of the EPP chips which data segment is to be sent and received in each time interval. The EPP chips then inform their local data slice chips as to which data segments are to be sent in each interval and which data segments will be received in each interval. As previously mentioned, the forwarding cards each send and receive data. The data slice chips include small buffers to hold certain data (e.g., lower priority) while other data (e.g., higher priority) data is sent and small buffers to store received data. The data slice chips also include header information with each segment of data sent to the switch fabric cards. The header information is used by cross-bar chips  672   a – 6721  (only cross-bar chips  672   a – 672   f  are shown) to switch the data to the correct forwarding card. The cross-bar chips may be PM9312-UC chips and the scheduler chip may be a PM9311-UC chip both of which are available from Abrizio. 
   Specifications for the EPD, Abrizio and PMC-Sierra chips may be found at www.pmc-sierra.com and are hereby incorporated herein by reference. 
   Distributed Switch Fabric Timing: 
   As previously mentioned, a segment of data (e.g., an ATM cell) is transferred between the data slice chips through the cross-bar chips every predetermined time interval. In one embodiment, this time interval is 40 ns and is established by a 25 MHz start of segment (SOS) signal. A higher frequency clock (e.g., 200 MHz, having a 5 ns time interval) is used by the data slice and cross-bar chips to transfer the bits of data within each segment such that all the bits of data in a segment are transferred within one 40 ns interval. More specifically, in one embodiment, each switch fabric component multiplies the 200 MHz clock signal by four to provide an 800 MHz internal clock signal allowing data to be transferred through the data slice and cross-bar components at 320 Gbps. As a result, every 40 ns one segment of data (e.g., an ATM cell) is transferred. It is crucial that the EPP, scheduler, data slice and cross-bar chips transfer data according to the same/synchronized timing signals (e.g., clock and SOS), including both frequency and phase. Transferring data at different times, even slightly different times, may lead to data corruption, the wrong data being sent and/or a network device crash. 
   When distributed signals (e.g., reference SOS or clock signals) are used to synchronize actions across multiple components (e.g., the transmission of data through a switch fabric), any time-difference in events (e.g., clock pulse) on the distributed signals is generally termed “skew”. Skew between distributed signals may result in the actions not occurring at the same time, and in the case of transmission of data through a switch fabric, skew can cause data corruption and other errors. Many variables can introduce skew into these signals. For example, components used to distribute the clock signal introduce skew, and etches on the mid-plane(s) introduce skew in proportion to the differences in their length (e.g., about 180 picoseconds per inch of etch in FR 4 printed circuit board material). 
   To minimize skew, one manufacturer teaches that all switch fabric components (i.e., scheduler, EPP, data slice and cross-bar chips) should be located on centralized switch fabric cards. That manufacturer also suggests distributing a central clock reference signal (e.g., 200 MHz) and a separate SOS signal (e.g., 25 MHz) to the switch fabric components on the switch fabric cards. Such a timing distribution scheme is difficult but possible where all the components are on one switch fabric card or on a limited number of switch fabric cards that are located near each other within the network device or in a separate box connected to the network device. Locating the boards near each other within the network device or in a separate box allows etch lengths on the mid-plane for the reference timing signals to be more easily matched and, thus, introduce less skew. 
   When the switch fabric components are distributed, maintaining a very tight skew becomes difficult due to the long lengths of etches required to reach some of the distributed cards and the routing difficulties that arise in trying to match the lengths of all the etches across the mid-plane(s). Because the clock signal needs to be distributed not only to the five switch fabric cards but also the forwarding cards (e.g., twenty), it becomes a significant routing problem to distribute all clocks to all loads with a fixed etch length. 
   Since timing is so critical to network device operation, typical network devices include redundant central timing subsystems. Certainly, the additional reference timing signals from a redundant central timing subsystem to each of the forwarding cards and switch fabric cards create further routing difficulties. In addition, if the two central timing subsystems (i.e., sources) are not synchronous with matched distribution etches, then all of the loads (i.e., LTSs) must use the same reference clock source to avoid introducing clock skew—that is, unless both sources are synchronous and have matched distribution networks, the reference timing signals from both sources are likely to be skewed with respect to each other and, thus, all loads must use the same source/reference timing signal or be skewed with respect to each other. 
   A redundant, distributed switch fabric greatly increases the number of reference timing signals that must be routed over the mid-planes and yet remain accurately synchronized. In addition, since the timing signals must be sent to each card having a distributed switch fabric, the distance between the cards may vary greatly and, thus, make matching the lengths of timing signal etches on the mid-planes difficult. Further, the lengths of the etches for the reference timing signals from both the primary and redundant central timing subsystems must be matched. Compounding this with a fast clock signal and low skew component requirements makes distributing the timing very difficult. 
   The network device of the present invention, though difficult, includes two synchronized central timing subsystems (CTS)  673  (one is shown in  FIG. 43 ). The etch lengths of reference timing signals from both central timing subsystems are matched to within, for example, +/−50 mils, and both central timing subsystems distribute only reference start of segment (SOS) signals to a local timing subsystem (LTS)  665  on each forwarding card and switch fabric card. The LTSs use the SOS reference signals to generate both an SOS signal and a higher frequency clock signal. This adds components and complexity to the LTSs, however, distributing only the SOS reference signals and not both the SOS and clock reference signals significantly reduces the number of reference timing signals that must be routed across the mid-plane on matched etch lengths. 
   Both electromagnetic radiation and electro-physical limitations prevent the 200 MHz reference clock signal from being widely distributed as required in a network device implementing distributed switch fabric subsystems. Such a fast reference clock increases the overall noise level generated by the network device and wide distribution may cause the network device to exceed Electro-Magnetic Interference (EMI) limitations. Clock errors are often measured as a percentage of the clock period, the smaller the clock period (5 ns for a 200 MHz clock), the larger the percentage of error a small skew can cause. For example, a skew of 3 ns represents a 60% error for a 5 ns clock period but only a 7.5% error for a 40 ns clock period. Higher frequency clock signals (e.g., 200 MHz) are susceptible to noise error and clock skew. The SOS signal has a larger clock period than the reference clock signal (40 ns versus 5 ns) and, thus, is less susceptible to noise error and reduces the percentage of error resulting from clock skew. 
   As previously mentioned, the network device may include redundant switch fabric cards  570   a  and  570   b  ( FIGS. 36   a – 36   b ) and as described above with reference to  FIG. 43 , each switch fabric card  570   a  and  570   b  may include a control card and four or more data cards. 
   Referring to  FIG. 44 , network device  540  may include switch fabric control card  666  (part of central switch fabric  570   a ) and redundant switch fabric control card  667  (part of redundant switch fabric  570   b ). Each control card  666  and  667  includes a central timing subsystem (CTS)  673 . One CTS behaves as the master and the other CTS behaves as a slave and locks its output SOS signal to the master&#39;s output SOS signal. In one embodiment, upon power-up or system re-boot the CTS on the primary switch fabric control card  666  begins as the master and if a problem occurs with the CTS on the primary control card, then the CTS on redundant control card  667  takes over as master without requiring a switch over of the primary switch fabric control card. 
   Still referring to  FIG. 44 , each CTS sends a reference SOS signal to the LTSs on each forwarding card, switch fabric data cards  668   a – 668   d  and redundant switch fabric data cards  669   a – 669   b.  In addition, each CTS sends a reference SOS signal to the LTS on its own switch fabric control card and the LTS on the other switch fabric control card. As described in more detail below, each LTS then selects which reference SOS signal to use. Each CTS  673  also sends a reference SOS signal to the CTS on the other control card. The master CTS ignores the reference SOS signal from the slave CTS but the slave CTS locks its reference SOS signal to the reference SOS signal from the master, as described below. Locking the slave SOS signal to the master SOS signal synchronizes the slave signal to the master signal such that in the event that the master CTS fails and the LTSs switchover to the slave CTS reference SOS signal and the slave CTS becomes the master CTS, minimal phase change and no signal disruption is encountered between the master and slave reference SOS signals received by the LTSs. 
   Each of the CTS reference SOS signals sent to the LTSs and the other CTS over mid-plane etches are the same length (i.e., matched) to avoid introducing skew. The CTS may be on its own independent card or any other card in the system. Even when it is located on a switch fabric card, such as the control card, that has an LTS, the reference SOS signal is routed through the mid-plane with the same length etch as the other reference SOS signals to avoid adding skew. 
   Central Timing Subsystem (CTS): 
   Referring to  FIGS. 45   a – 45   b , central timing subsystem (CTS)  673  includes a voltage controlled crystal oscillator (VCXO)  676  that generates a 25 MHz reference SOS signal  678 . The SOS signal must be distributed to each of the local timing subsystems (LTSs) and is, thus, sent to a first level clock driver  680  and then to second level clock drivers  682   a – 682   d  that output reference SOS signals SFC_BENCH_FB and SFC_REF 1 –SFC_REFn. SFC_BENCH_FB is a local feedback signal returned to the input of the CTS. One of SFC_REF 1 –SFC_REFn is sent to each LTS, the other CTS, which receives it on SFC_SYNC, and one is routed over a mid-plane and returned as a feedback signal SFC_FB to the input of the CTS that generated it. Additional levels of clock drivers may be added as the number of necessary reference SOS signals increases. 
   VCXO  676  may be a VF596ES50 25 MHz LVPECL available from Conner-Winfield. Positive Emitter Coupled Logic (PECL) is preferred over Transistor-Transistor Logic (TTL) for its lower skew properties. In addition, though it requires two etches to transfer a single clock reference—significantly increasing routing resources—, differential PECL is preferred over PECL for its lower skew properties and high noise immunity. The clock drivers are also differential PECL and may be one to ten (1:10) MC100 LVEP111 clock drivers available from On Semiconductor. A test header  681  may be connected to clock driver  680  to allow a test clock to be input into the system. 
   Hardware control logic  684  determines (as described below) whether the CTS is the master or slave, and hardware control logic  684  is connected to a multiplexor (MUX)  686  to select between a predetermined voltage input (i.e., master voltage input)  688   a  and a slave VCXO voltage input  688   b.  When the CTS is the master, hardware control logic  684  selects predetermined voltage input  688   a  from discrete bias circuit  690  and slave VCXO voltage input  688   b  is ignored. The predetermined voltage input causes VCXO  676  to generate a constant 25 MHz SOS signal; that is, the VCXO operates as a simple oscillator. 
   Hardware control logic may be implemented in a field programmable gate array (FPGA) or a programmable logic device (PLD). MUX  686  may be a 74CBTLV3257 FET 2:1 MUX available from Texas Instruments. 
   When the CTS is the slave, hardware control logic  684  selects slave VCXO voltage signal  688   b.  This provides a variable voltage level to the VCXO that causes the output of the VCXO to track or follow the SOS reference signal from the master CTS. Referring still to  FIGS. 45   a – 45   b , the CTS receives the SOS reference signal from the other CTS on SFC_SYNC. Since this is a differential PECL signal, it is first passed through a differential PECL to TTL translator  692  before being sent to MUX  697   a  within dual MUX  694 . In addition, two feedback signals from the CTS itself are supplied as inputs to the CTS. The first feedback signal SFC_FB is an output signal (e.g., one of SFC_REF 1 –SFC_REFn) from the CTS itself which has been sent out to the mid-plane and routed back to the switch fabric control card. This is done so that the feedback signal used by the CTS experiences identical conditions as the reference SOS signal delivered to the LTSs and skew is minimized. The second feedback signal SFC_BENCH_FB is a local signal from the output of the CTS, for example, clock driver  682   a.  SFC_BENCH_FB may be used as the feedback signal in a test mode, for example, when the control card is not plugged into the network device chassis and SFC_SB is unavailable. SFC_BENCH_FB and SFC_FB are also differential PECL signals and must be sent through translators  693  and  692 , respectively, prior to being sent to MUX  697   b  within dual MUX  694 . Hardware control logic  684  selects which inputs are used by MUX  694  by asserting signals on REF_SEL( 1 : 0 ) and FB_SEL( 1 : 0 ). In regular use, inputs  696   a  and  696   b  from translator  692  are selected. In test modes, grounded inputs  695   a,  test headers  695   b  or local feedback signal  698  from translator  693  may be selected. Also in regular use (and in test modes where a clock signal is not inserted through the test headers), copies of the selected input signals are provided on the test headers. 
   The reference output  700   a  and the feedback output  700   b  are then sent from the MUX to phase detector circuit  702 . The phase detector compares the rising edge of the two input signals to determine the magnitude of any phase shift between the two. The phase detector then generates variable voltage pulses on outputs  704   a  and  704   b  representing the magnitude of the phase shift. The phase detector outputs are used by discrete logic circuit  706  to generate a voltage on a slave VCXO voltage signal  688   b  representing the magnitude of the phase shift. The voltage is used to speed up or slow down (i.e., change the phase of) the VCXO&#39;s output SOS signal to allow the output SOS signal to track any phase change in the reference SOS signal from the other CTS (i.e., SFC_SYNC). The discrete logic components implement filters that determine how quickly or slowly the VCXO&#39;s output will track the change in phase detected on the reference signal. The combination of the dual MUX, phase detector, discrete logic, VCXO, clock drivers and feedback signal forms a phase locked loop (PLL) circuit allowing the slave CTS to synchronize its reference SOS signal to the master CTS reference SOS signal. MUX  686  and discrete bias circuit  690  are not found in phase locked loop circuits. 
   The phase detector circuit may be implemented in a programmable logic device (PLD), for example a MACH4LV-32 available from Lattice/Vantis Semiconductor. Dual MUX  694  may be implemented in the same PLD. Preferably, however, dual MUX  694  is an SN74CBTLV3253 available from Texas Instruments, which has better skew properties than the PLD. The differential PECL to TTL translators may be MC100EPT23 dual differential PECL/TTL translators available from On Semiconductor. 
   Since quick, large phase shifts in the reference signal are likely to be the results of failures, the discrete logic implements a filter, and for any detected phase shift, only small incremental changes over time are made to the voltage provided on slave VCXO control signal  688   b.  As one example, if the reference signal from the master CTS dies, the slave VCXO control signal  688   b  only changes phase slowly over time meaning that the VCXO will continue to provide a reference SOS signal. If the reference signal from the master CTS is suddenly returned, the slave VCXO control signal  688   b  again only changes phase slowly over time to cause the VCXO signal to re-synchronize with the reference signal from the master CTS. This is a significant improvement over distributing a clock signal directly to components that use the signal because, in the case of direct clock distribution, if one clock signal dies (e.g., broken wire), then the components connected to that signal stop functioning causing the entire switch fabric to fail. 
   Slow phase changes on the reference SOS signals from both the master and slave CTSs are also important when LTSs switch over from using the master CTS reference signal to using the slave CTS reference signal. For example, if the reference SOS signal from the master CTS dies or other problems are detected (e.g., a clock driver dies), then the slave CTS switches over to become the master CTS and each of the LTSs begin using the slave CTS′ reference SOS signal. For these reasons, it is important that the slave CTS reference SOS signal be synchronized to the master reference signal but not quickly follow large phase shifts in the master reference signal. 
   It is not necessary for every LTS to use the reference SOS signals from the same CTS. In fact, some LTSs may use reference SOS signals from the master CTS while one or more are using the reference SOS signals from the slave CTS. In general, this is a transitional state prior to or during switch over. For example, one or more LTSs may start using the slave CTS&#39;s reference SOS signal prior to the slave CTS switching over to become the master CTS. 
   It is important for both the CTSs and the LTSs to monitor the activity of the reference SOS signals from both CTSs such that if there is a problem with one, the LTSs can begin using the other SOS signal immediately and/or the slave CTS can quickly become master. Reference output signal  700   a —the translated reference SOS signal sent from the other CTS and received on SFC_SYNC—is sent to an activity detector circuit  708 . The activity detector circuit determines whether the signal is active—that is, whether the signal is “stuck at” logic 1 or logic 0. If the signal is not active (i.e., stuck at logic 1 or 0), the activity detector sends a signal  683   a  to hardware control logic  684  indicating that the signal died. The hardware control logic may immediately select input  688   a  to MUX  686  to change the CTS from slave to master. The hardware control logic also sends an interrupt to a local processor  710  and software being executed by the processor detects the interrupt. Hardware control allows the CTS switch over to happen very quickly before a bad clock signal can disrupt the system. 
   Similarly, an activity detector  709  monitors the output of the first level clock driver  680  regardless of whether the CTS is master or slave. Instead, the output of one the second level clock drivers could be monitored, however, a failure of a different second level clock will not be detected. SFC_REF_ACTIVITY is sent from the first level clock driver to differential PECL to TTL translator  693  and then as FABRIC_REF_ACTIVITY to activity detector  709 . If activity detector  709  determines that the signal is not active, which may indicate that the clock driver, oscillator or other component(s) within the CTS have failed, then it sends a signal  683   b  to the hardware control logic. The hardware control logic asserts KILL_CLKTREE to stop the clock drivers from sending any signals and notifies a processor chip  710  on the switch fabric control card through an interrupt. Software being executed by the processor chip detects the interrupt. The slave CTS activity detector  708  detects a dead signal from the master CTS either before or after the hardware control logic sends KILL_CLKTREE and asserts error signal  683   a  to cause the hardware control logic to change the input selection on MUX  686  from  688   b  to  688   a  to become the master CTS. As described below, the LTSs also detect a dead signal from the master CTS either before or after the hardware control logic sends KILL_CLKTREE and switch over to the reference SOS signal from the slave CTS either before or after the slave CTS switches over to become the master. 
   As previously mentioned, in the past, a separate, common clock selection signal or etch was sent to each card in the network device to indicate whether to use the master or slave clock reference signal. This approach required significant routing resources, was under software control and resulted in every load selecting the same source at any given time. Hence, if a clock signal problem was detected, components had to wait for the software to change the separate clock selection signal before beginning to use the standby clock signal and all components (i.e., loads) were always locked to the same source. This delay can cause data corruption errors, switch fabric failure and a network device crash. 
   Forcing a constant logic one or zero (i.e., “killing”) clock signals from a failed source and having hardware in each LTS and CTS detect inactive (i.e., “dead” or stuck at logic one or zero) signals allows the hardware to quickly begin using the standby clock without the need for software intervention. In addition, if only one clock driver (e.g.,  682   b ) dies in the master CTS, LTSs receiving output signals from that clock driver may immediately begin using signals from the slave CTS clock driver while the other LTSs continue to use the master CTS. Interrupts to the processor from each of the LTSs connected to the failed master CTS clock driver allow software, specifically the SRM, to detect the failure and initiate a switch over of the slave CTS to the master CTS. The software may also override the hardware control and force the LTSs to use the slave or master reference SOS signal. 
   When the slave CTS switches over to become the master CTS, the remaining switch fabric control card functionality (e.g., scheduler and cross-bar components) continue operating. The SRM (described above) decides—based on a failure policy—whether to switch over from the primary switch fabric control card to the secondary switch fabric control card. There may be instances where the CTS on the secondary switch fabric control card operates as the master CTS for a period of time before the network device switches over from the primary to the secondary switch fabric control card, or instead, there may be instances where the CTS on the secondary switch fabric control card operates as the master CTS for a period of time and then the software directs the hardware control logic on both switch fabric control cards to switch back such that the CTS on the primary switch fabric control card is again master. Many variations are possible since the CTS is independent of the remaining functionality on the switch fabric control card. 
   Phase detector  702  also includes an out of lock detector that determines whether the magnitude of change between the reference signal and the feedback signal is larger than a predetermined threshold. When the CTS is the slave, this circuit detects errors that may not be detected by activity detector  708  such as where the reference SOS signal from the master CTS is failing but is not dead. If the magnitude of the phase change exceeds the predetermined threshold, then the phase detector asserts an OOL signal to the hardware control logic. The hardware control logic may immediately change the input to MUX  686  to cause the slave CTS to switch over to Master CTS and send an interrupt to the processor, or the hardware control logic may only send the interrupt and wait for software (e.g., the SRM) to determine whether the slave CTS should switch over to master. 
   Master/Slave CTS Control: 
   In order to determine which CTS is the master and which is the slave, hardware control logic  684  implements a state machine. Each hardware control logic  684  sends an IM_THE_MASTER signal to the other hardware control logic  684  which is received as a YOU_THE_MASTER signal. If the IM_THE_MASTER signal—and, hence, the received YOU_THE_MASTER signal—is asserted then the CTS sending the signal is the master (and selects input  688   a  to MUX  686 ,  FIGS. 45   a – 45   b ) and the CTS receiving the signal is the slave (and selects input  688   b  to MUX  686 ). Each IM_THE_MASTER/YOU_THE_MASTER etch is pulled down to ground on the mid-planes such that if one of the CTSs is missing, the YOU_THE_MASTER signal received by the other CTS will be a logic 0 causing the receiving CTS to become the master. This situation may arise, for example, if a redundant control card including the CTS is not inserted within the network device. In addition, each of the hardware control logics receive SLOT_ID signals from pull-down/pull-up resistors on the chassis mid-plane indicating the slot in which the switch fabric control card is inserted. 
   Referring to  FIG. 46 , on power-up or after a system or card or CTS re-boot, the hardware control logic state machine begins in INIT/RESET state 0 and does not assert IM_THE_MASTER. If the SLOT_ID signals indicate that the control card is inserted in a preferred slot (e.g., slot one), and the received YOU_THE_MASTER is not asserted (i.e., 0), then the state machine transitions to the ONLINE state  3  and the hardware control logic asserts IM_THE_MASTER indicating its master status to the other CTS and selects input  688   a  to MUX  686 . While in the ONLINE state  3 , if a failure is detected or the software tells the hardware logic to switch over, the state machine enters the OFFLINE state  1  and the hardware control logic stops asserting IM_THE_MASTER and asserts KILL_CLKTREE. While in the OFFLINE state  1 , the software may reset or re-boot the control card or just the CTS and force the state machine to enter the STANDBY state  2  as the slave CTS and the hardware control logic stops asserting KILL_CLKTREE and selects input  688   b  to MUX  686 . 
   While in INIT/RESET state  0 , if the SLOT_ID signals indicate that the control card is inserted in a non-preferred slot, (e.g., slot  0 ), then the state machine will enter STANDBY state  2  as the slave CTS and the hardware control logic will not assert IM_THE_MASTER and will select input  688   b  to MUX  686 . While in INIT/RESET state  0 , even if the SLOT-ID signals indicate that the control card is inserted in the preferred slot, if YOU_THE_MASTER is asserted, indicating that the other CTS is master, then the state machine transfers to STANDBY state  2 . This situation may arise after a failure and recovery of the CTS in the preferred slot (e.g., reboot, reset or new control card). 
   A While in the STANDBY state  2 , if the YOU_THE_MASTER signal becomes zero (i.e., not asserted), indicating that the master CTS is no longer master, the state machine will transition to ONLINE state  3  and the hardware control logic will assert IM_THE_MASTER and select input  688   a  to MUX  686  to become master. While in ONLINE state  3 , if the YOU_THE_MASTER signal is asserted and SLOT_ID indicating slot  0  the state machine enters STANDBY state  2  and the hardware control logic stops asserting IM_THE_MASTER and selects input  688   b  to MUX  686 . This is the situation where the original master CTS is back up and running. The software may reset the state machine at any time or set the state machine to a particular state at any time. 
   Local Timing Subsystem: 
   Referring to  FIGS. 47   a – 47   b , each local timing subsystem (LTS) 665 receives a reference SOS signal from each CTS on SFC_REFA and SFC_REFB. Since these are differential PECL signals, each is passed through a differential PECL to TTL translator  714   a  or  714   b,  respectively. A feedback signal SFC_FB is also passed from the LTS output to both translators  714   a  and  714   b.  The reference signal outputs  716   a  and  716   b  are fed into a first MUX  717  within dual MUX  718 , and the feedback signal outputs  719   a  and  719   b  are fed into a second MUX  720  within dual MUX  718 . LTS hardware control logic  712  controls selector inputs REF_SEL ( 1 : 0 ) and FB_SEL ( 1 : 0 ) to dual MUX  718 . With regard to the feedback signals, the LTS hardware control logic selects the feedback signal that went through the same translator as the reference signal that is selected to minimize the effects of any skew introduced by the two translators. 
   A phase detector  722  receives the feedback (FB) and reference (REF) signals from the dual MUX and, as explained above, generates an output in accordance with the magnitude of any phase shift detected between the two signals. Discrete logic circuit  724  is used to filter the output of the phase detector, in a manner similar to discrete logic  706  in the CTS, and provide a signal to VCXO  726  representing a smaller change in phase than that output from the phase detector. Within the LTSs, the VCXO is a 200 MHz oscillator as opposed to the 25 MHz oscillator used in the CTS. The output of the VCXO is the reference switch fabric clock. It is sent to clock driver  728 , which fans the signal out to each of the local switch fabric components. For example, on the forwarding cards, the LTSs supply the 200 MHz reference clock signal to the EPP and data slice chips, and on the switch fabric data cards, the LTSs supply the 200 MHz reference clock signal to the cross-bar chips. On the switch fabric control card, the LTSs supply the 200 MHz clock signal to the scheduler and cross-bar components. 
   The 200 MHz reference clock signal from the VCXO is also sent to a divider circuit or component  730  that divides the clock by eight to produce a 25 MHz reference SOS signal  731 . This signal is sent to clock driver  732 , which fans the signal out to each of the same local switch fabric components that the 200 MHz reference clock signal was sent to. In addition, reference SOS signal  731  is provided as feedback signal SFC_FB to translator  714   b.  The combination of the dual MUX, phase detector, discrete logic, VCXO, clock drivers and feedback signal forms a phase locked loop circuit allowing the 200 MHz and 25 MHz signals generated by the LTS to be synchronized to either of the reference SOS signals sent from the CTSs. 
   The divider component may be a SY100EL34L divider by Synergy Semiconductor Corporation. 
   Reference signals  716   a  and  716   b  from translator  714   a  are also sent to activity detectors  734   a  and  734   b,  respectively. These activity detectors perform the same function as the activity detectors in the CTSs and assert error signals ref_a_los or ref_b_los to the LTS hardware control logic if reference signal  716   a  or  716   b,  respectively, die. On power-up, reset or reboot, a state machine ( FIG. 48 ) within the LTS hardware control logic starts in INIT/RESET state  0 . Arbitrarily, reference signal  716   a  is the first signal considered. If activity detector  734   a  is not sending an error signal (i.e., ref_a_los is 0), indicating that that reference signal  716   a  is active, then the state machine changes to REF_A state  2  and sends signals over REF_SEL( 1 : 0 ) to MUX  717  to select reference input  716   a  and sends signals over FB_SEL( 1 : 0 ) to MUX  720  to select feedback input  719   a.  While in INIT/RESET state  0 , if ref a los is asserted, indicating no signal on reference  716   a,  and if ref_b_los is not asserted, indicating there is a signal on reference  716   b,  then the state machine changes to REF_B state  1  and changes REF_SEL( 1 : 0 ) and FB_SEL( 1 : 0 ) to select reference input  716   b  and feedback signal  719   b.    
   While in REF_A state  2 , if activity detector  734   a  detects a loss of reference signal  716   a  and asserts ref_a_los, the state machine will change to REF_B state  1  and change REF_SEL( 1 : 0 ) and FB_SEL( 1 : 0 ) to select inputs  716   b  and  719   b.  Similarly, while in REF_B state  1 , if activity detector  734   b  detects a loss of signal  716   b  and asserts ref_b_los, the state machine will change to REF_A state  2  and change REF_SEL( 1 : 0 ) and FB_SEL( 1 : 0 ) to select inputs  716   a  and  719   a.  While in either REF_A state  2  or REF_B state  1 , if both ref_a_los and ref_b_los are asserted, indicating that both reference SOS signals have died, the state machine changes back to INIT/RESET state  0  and change REF_SEL( 1 : 0 ) and FB_SEL( 1 : 0 ) to select no inputs or test inputs  736   a  and  736   b  or ground  738 . For a period of time, the LTS will continue to supply a clock and SOS signal to the switch fabric components even though it is receiving no input reference signal. 
   When ref_a_los and/or ref_b_los are asserted, the LTS hardware control logic notifies its local processor  740  through an interrupt. The SRM will decide, based on a failure policy, what actions to take, including whether to switch over from the master to slave CTS. Just as the phase detector in the CTS sends an out of lock signal to the CTS hardware control logic, the phase detector  722  also sends an out of lock signal OOL to the LTS hardware control logic if the magnitude of the phase difference between the reference and feedback signals exceeds a predetermined threshold. If the LTS hardware receives an asserted OOL signal, it notifies its local processor (e.g.,  740 ) through an interrupt. The SRM will decide based on a failure policy what actions to take. 
   Shared LTS Hardware: 
   In the embodiment described above, the switch fabric data cards are four independent cards. More data cards may also be used. Alternatively, all of the cross-bar components may be located on one card. As another alternative, half of the cross-bar components may be located on two separate cards and yet attached to the same network device faceplate and share certain components. A network device faceplate is something the network manager can unlatch and pull on to remove cards from the network device. Attaching two switch fabric data cards to the same faceplate effectively makes them one board since they are added to and removed from the network device together. Since they are effectively one board, they may share certain hardware as if all components were on one physical card. In one embodiment, they may share a processor, hardware control logic and activity detectors. This means that these components will be on one of the physical cards but not on the other and signals connected to the two cards allow activity detectors on the one card to monitor the reference and feedback signals on the other card and allow the hardware control logic on the one card to select the inputs for dual MUX  718  on the other card. 
   Scheduler: 
   Another difficulty with distributing a portion of the switch fabric functionality involves the scheduler component on the switch fabric control cards. In current systems, the entire switch fabric, including all EPP chips, are always present in a network device. Registers in the scheduler component are configured on power-up or re-boot to indicate how many EPP chips are present in the current network device, and in one embodiment, the scheduler component detects an error and switches over to the redundant switch fabric control card when one of those EPP chips is no longer active. When the EPP chips are distributed to different cards (e.g., forwarding cards) within the network device, an EPP chip may be removed from a running network device when the printed circuit board on which it is located is removed (“hot swap”, “hot removal”) from the network device. To prevent the scheduler chip from detecting the missing EPP chip as an error (e.g., a CRC error) and switching over to the redundant switch fabric control card, prior to the board being removed from the network device, software running on the switch fabric control card re-configures the scheduler chip to disable the scheduler chip&#39;s links to the EPP chip that is being removed. 
   To accomplish this, a latch  547  ( FIG. 40 ) on the faceplate of each of the printed circuit boards on which a distributed switch fabric is located is connected to a circuit  742  ( FIG. 44 ) also on the printed circuit board that detects when the latch is released. When the latch is released, indicating that the board is going to be removed from the network device, circuit  742  sends a signal to a circuit  743  on both switch fabric control cards indicating that the forwarding card is about to be removed. Circuit  743  sends an interrupt to the local processor (e.g.,  710 ,  FIGS. 45   a – 45   b ) on the switch fabric control card. Software (e.g., slave SRM) being executed by the local processor detects the interrupt and sends a notice to software (e.g., master SRM) being executed by the processor (e.g.,  24 ,  FIG. 1 ) on the network device centralized processor card (e.g.,  12 ,  FIG. 1 ,  542  or  543 ,  FIGS. 35   a – 35   b ). The master SRM sends a notice to the slave SRMs being executed by the processors on the switch fabric data cards and forwarding cards to indicate the removal of the forwarding card. The redundant forwarding card switches over to become a replacement for the failed primary forwarding card. The master SRM also sends a notice to the slave SRM on the cross-connection card (e.g.,  562 – 562   b,    564   a – 564   b,    566   a – 566   b,    568   a – 565   b,    FIGS. 35   a – 35   b ) to re-configure the connections between the port cards (e.g.,  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h,    FIGS. 35   a – 35   b ) and the redundant forwarding card. The slave SRM on the switch fabric control card re-configures the registers in the scheduler component to disable the scheduler&#39;s links to the EPP chip on the forwarding card that&#39;s being removed from the network device. As a result, when the forwarding card is removed, the scheduler will not detect an error due to a missing EPP chip. 
   Similarly, when a forwarding card is added to the network device, circuit  742  detects the closing of the latch and sends an interrupt to the processor. The slave SRM running on the local processor sends a notice to the Master SRM which then sends a notice to the slave SRMs being executed by the processors on the switch fabric control cards, data cards and forwarding cards indicating the presence of the new forwarding card. The slave SRM on the cross-connection cards may be re-configured, and the slave SRM on the switch fabric control card may re-configure the scheduler chip to establish links with the new EPP chip to allow data to be transferred to the newly added forwarding card. 
   Switch Fabric Control Card Switch-Over: 
   Typically, the primary and secondary scheduler components receive the same inputs, maintain the same state and generate the same outputs. The EPP chips are connected to both scheduler chips but only respond to the master/primary scheduler chip. If the primary scheduler or control card experiences a failure a switch over is initiated to allow the secondary scheduler to become the primary. When the failed switch fabric control card is re-booted, re-initialized or replaced, it and its scheduler component serve as the secondary switch fabric control card and scheduler component. 
   In currently available systems, a complex sequence of steps is required to “refresh” or synchronize the state of the newly added scheduler component to the primary scheduler component and for many of these steps, network data transfer through the switch fabric is temporarily stopped (i.e., back pressure). Stopping network data transfer may affect the availability of the network device. When the switch fabric is centralized and all on one board or only a few boards or in its own box, the refresh steps are quickly completed by one or only a few processors limiting the amount of time that network data is not transferred. When the switch fabric includes distributed switch fabric subsystems, the processors that are local to each of the distributed switch fabric subsystems must take part in the series of steps. This may increase the amount of time that data transfer is stopped further affecting network device availability. 
   To limit the amount of time that data transfer is stopped in a network device including distributed switch fabric subsystems, the local processors each set up for a refresh while data is still being transferred. Communications between the processors take place over the Ethernet bus (e.g.,  32 ,  FIG. 1 ,  544 ,  FIGS. 35   a – 35   b ) to avoid interrupting network data transfer. When all processors have indicated (over the Ethernet bus) that they are ready for the refresh, the processor on the master switch fabric control card stops data transfer and sends a refresh command to each of the processors on the forwarding cards and switch fabric cards. Since all processors are waiting to complete the refresh, it is quickly completed. Each processor notifies the processor on the master switch fabric control card that the refresh is complete, and when all processors have completed the refresh, the master switch fabric control card re-starts the data transfer. 
   During the time in which the data transfer is stopped, the buffers in the traffic management chips are used to store data coming from external network devices. It is important that the data transfer be complete quickly to avoid overrunning the traffic management chip buffers. 
   Since the switch over of the switch fabric control cards is very complex and requires that data transfer be stopped, even if briefly, it is important that the CTSs on each switch fabric control card be independent of the switch fabric functionality. This independence allows the master CTS to switch over to the slave CTS quickly and without interrupting the switch fabric functionality or data transmission. 
   As described above, locating the EPP chips and data slice chips of the switch fabric subsystem on the forwarding cards is difficult and against the teachings of a manufacturer of these components. However, locating these components on the forwarding cards allows the base network device—that is, the minimal configuration—to include only a necessary portion of the switching fabric reducing the cost of a minimally configured network device. As additional forwarding cards are added to the minimal configuration—to track an increase in customer demand—additional portions of the switch fabric are simultaneously added since a portion of the switch fabric is located on each forwarding card. Consequently, switch fabric growth tracks the growth in customer demands and fees. Also, typical network devices include 1:1 redundant switch fabric subsystems. However, as previously mentioned, the forwarding cards may be 1:N redundant and, thus, the distributed switch fabric on each forwarding card is also 1:N redundant further reducing the cost of a minimally configured network device. 
   External Network Data Transfer Timing: 
   In addition to internal switch fabric timing, a network device must also include external network data transfer timing to allow the network device to transfer network data synchronously with other network devices. Generally, multiple network devices in the same service provider site synchronize themselves to Building Integrated Timing Supply (BITS) lines provided by a network service provider. BITS lines are typically from highly accurate stratum two clock sources. In the United States, standard T1 BITS lines (2.048 MHz) are provided, and in Europe, standard E1 BITS lines (1.544 MHz) are provided. Typically, a network service provider provides two T1 lines or two E1 lines from different sources for redundancy. Alternatively, if there are no BITS lines or when network devices in different sites want to synchronously transfer data, one network device may extract a timing signal received on a port connected to the other network device and use that timing signal to synchronize its data transfers with the other network device. 
   Referring to  FIG. 49 , controller card  542   b  and redundant controller card  543   b  each include an external central timing subsystem (EX CTS)  750 . Each EX CTS receives BITS lines  751  and provide BITS lines  752 . In addition, each EX CTS receives a port timing signal  753  from each port card ( 554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h,    FIGS. 35   a – 35   b ), and each EX CTS also receives an external timing reference signal  754  from itself and an external timing reference signal  755  from the other EX CTS. 
   One of the EX CTSs behaves as a master and the other EX CTS behaves as a slave. The master EX CTS may synchronize its output external reference timing signals to one of BITS lines  751  or one of the port timing signals  753 , while the slave EX CTS synchronizes its output external reference timing signals to the received master external reference timing signal  755 . Upon a master EX CTS failure, the slave EX CTS may automatically switch over to become the master EX CTS or software may upon an error or at any time force the slave EX CTS to switch over to become the master EX CTS. 
   An external reference timing signal from each EX CTS is sent to each external local timing subsystem (EX LTS)  756  on cards throughout the network device, and each EX LTS generates local external timing signals synchronized to one of the received external reference timing signals. Generally, external reference timing signals are sent only to cards including external data transfer functionality, for example, cross connection cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b  and  568   a – 568   b  ( FIGS. 35   a – 35   b ) and universal port cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h.    
   In network devices having multiple processor components, an additional central processor timing subsystem is needed to generate processor timing reference signals to allow the multiple processors to synchronize certain processes and functions. The addition of both external reference timing signals (primary and secondary) and processor timing reference signals (primary and secondary) require significant routing resources. In one embodiment of the invention, the EX CTSs embed a processor timing reference signal within each external timing reference signal to reduce the number of timing reference signals needed to be routed across the mid-plane(s). The external reference timing signals are then sent to EX LTSs on each card in the network device having a processor component, for example, cross connection cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b,    568   a – 568   b,  universal port cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h,  forwarding cards  546   a – 546   e,    548   a – 548   e,    550   a – 550   e,    552   a – 552   e,  switch fabric cards  666 ,  667 ,  668   a – 668   d,    669   a – 669   d  ( FIG. 44 ) and both the internal controller cards  542   a,    543   a  ( FIG. 41   b ) and external controller cards  542   b  and  543   b.    
   All of the EX LTSs extract out the embedded processor reference timing signal and send it to their local processor component. Only the cross-connection cards and port cards use the external reference timing signal to synchronize external network data transfers. As a result, the EX LTSs include extra circuitry not necessary to the function of cards not including external data transfer functionality, for example, forwarding cards, switch fabric cards and internal controller cards. The benefit of reducing the necessary routing resources, however, out weighs any disadvantage related to the excess circuitry. In addition, for the cards including external data transfer functionality, having one EX LTS that provides both local signals actually saves resources on those cards, and separate processor central timing subsystems are not necessary. Moreover, embedding the processor timing reference signal within the highly accurate, redundant external timing reference signal provides a highly accurate and redundant processor timing reference signal. Furthermore having a common EX LTS on each card allows access to the external timing signal for future modifications and having a common EX LTS, as opposed to different LTSs for each reference timing signal, results in less design time, less debug time, less risk, design re-use and simulation re-use. 
   Although the EX CTSs are described as being located on the external controllers  542   b  and  543   b,  similar to the switch fabric CTSs described above, the EX CTSs may be located on their own independent cards or on any other cards in the network device, for example, internal controllers  542   a  and  543   a.  In fact, one EX CTS could be located on an internal controller while the other is located on an external controller. Many variations are possible. In addition, just as the switch fabric CTSs may switch over from master to slave without affecting or requiring any other functionality on the local printed circuit board, the EX CTSs may also switch over from master to slave without affecting or requiring any other functionality on the local printed circuit board. 
   External Central Timing Subsystem (EX CTS): 
   Referring to  FIGS. 50   a – 50   c , EX CTS  750  includes a T1/E1 framer/LIU  758  for receiving and terminating BITS signals  751  and for generating and sending BITS signals  752 . Although T1/E1 framer is shown in two separate boxes in  FIGS. 50   a – 50   c , it is for convenience only and may be the same circuit or component. In one embodiment, two  5431  T1/E1 Framer Line Interface Units (LIU) available from PMC-Sierra are used. The T1/E1 framer supplies 8 KHz BITS_REF 0  and BITS_REF 1  signals and receives 8 KHz BITS 1 _TXREF and BITS 2 _TXREF signals. A network administrator notifies NMS  60  ( FIGS. 35   a – 35   b ) as to whether the BITS signals are T1 or E1, and the NMS notifies software running on the network device. Through signals  761  from a local processor, hardware control logic  760  within the EX CTS is configured for T1 or E1 and sends an T1E1_MODE signal to the T1/E1 framer indicating T1 or E1 mode. The T1/E1 framer then forwards BITS_REF 0  and BITS_REF 1  to dual MUXs  762   a  and  762   b.    
   Port timing signals  753  are also sent to dual MUXs  762   a  and  762   b . The network administrator also notifies the NMS as to which timing reference signals should be used, the BITS lines or the port timing signals. The NMS again notifies software running on the network device and through signals  761 , the local processor configures the hardware control logic. The hardware control logic then uses select signals  764   a  and  764   b  to select the appropriate output signals from the dual MUXs. 
   Activity detectors  766   a  and  766   b  provide status signals  767   a  and  767   b  to the hardware control logic indicating whether the PRI_REF signal and the SEC_REF signal are active or inactive (i.e., stuck at 1 or 0). The PRI_REF and SEC_REF signals are sent to a stratum 3 or stratum 3E timing module  768 . Timing module  768  includes an internal MUX for selecting between the PRI_REF and SEC_REF signals, and the timing module receives control and status signals  769  from the hardware control logic indicating whether PRI_REF or SEC_REF should be used. If one of the activity detectors  766   a  or  766   b  indicates an inactive status to the hardware control logic, then the hardware control logic sends appropriate information over control and status signals  769  to cause the timing module to select the active one of PRI_REF or SEC_REF. 
   The timing module also includes an internal phase locked loop (PLL) circuit and an internal stratum 3 or 3E oscillator. The timing module synchronizes its output signal  770  to the selected input signal (PRI_REF or SEC_REF). The timing module may be an MSTM-S3 available from Conner-Winfield or an ATIMe-s or ATIMe-3E available from TF systems. The hardware control logic, activity detectors and dual MUXs may be implemented in an FPGA. The timing module also includes a Free-run mode and a Hold-Over mode. When there is no input signal to synchronize to, the timing module enter a free-run mode and uses the internal oscillator to generate a clock output signal. If the signal being synchronized to is lost, then the timing module enters a hold-over mode and maintains the frequency of the last known clock output signal for a period of time. 
   The EX CTS  750  also receives an external timing reference signal from the other EX CTS on STRAT_SYNC  755  (one of STRAT_REF 1 –STRAT_REFN from the other EX CTS). STRAT_SYNC and output  770  from the timing module are sent to a MUX  772   a . REF_SEL( 1 : 0 ) selection signals are sent from the hardware control logic to MUX  772   a  to select STRAT_SYNC when the EX CTS is the slave and output  770  when the EX CTS is the master. When in a test mode, the hardware control logic may also select a test input from a test header  771   a.    
   An activity detector  774   a  monitors the status of output  770  from the timing module and provides a status signal to the hardware control logic. Similarly, an activity detector  774   b  monitors the status of STRAT_SYNC and provides a status signal to the hardware control logic. When the EX CTS is master, if the hardware control logic receives an inactive status from activity detector  774   a,  then the hardware control logic automatically changes the REF_SEL signals to select STRAT_SYNC forcing the EX CTS to switch over and become the slave. When the EX CTS is slave, if the hardware control logic receives an inactive status from activity detector  774   b,  then the hardware control logic may automatically change the REF_SEL signals to select output  770  from the timing module forcing the EX CTS to switch over and become master. 
   A MUX  772   b  receives feedback signals from the EX CTS itself. BENCH_FB is an external timing reference signal from the EX CTS that is routed back to the MUX on the local printed circuit board. STRAT_FB  754  is an external timing reference signal from the EX CTS (one of STRAT_REF 1 _STRAT_REFN) that is routed onto the mid-plane(s) and back onto the local printed circuit board such that is most closely resembles the external timing reference signals sent to the EX LTSs and the other EX CTS in order to minimize skew. The hardware control logic sends FB_SEL( 1 : 0 ) signals to MUX  772   b  to select STRAT_FB in regular use or BENCH_FB or an input from a test header  771   b  in test mode. 
   The outputs of both MUX  772   a  and 772 b  are provided to a phase detector  776 . The phase detector compares the rising edge of the two input signals to determine the magnitude of any phase shift between the two. The phase detector then generates variable voltage pulses on outputs  777   a  and  777   b  representing the magnitude of the phase shift. The phase detector outputs are used by discrete logic circuit  778  to generate a voltage on signal  779  representing the magnitude of the phase shift. The voltage is used to speed up or slow down (i.e., change the phase of) a VCXO  780  to allow the output signal  781  to track any phase change in the external timing reference signal received from the other EX CTS (i.e., STRAT_SYNC) or to allow the output signal  781  to track any phase change in the output signal  770  from the timing module. The discrete logic components implement a filter that determines how quickly or slowly the VCXO&#39;s output tracks the change in phase detected on the reference signal. 
   The phase detector circuit may be implemented in a programmable logic device (PLD). 
   The output  781  of the VCXO is sent to an External Reference Clock (ERC) circuit  782  which may also be implemented in a PLD. ERC_STRAT_SYNC is also sent to ERC  782  from the output of MUX  772   a . When the EX CTS is the master, the ERC circuit generates the external timing reference signal  784  with an embedded processor timing reference signal, as described below, based on the output signal  781  and synchronous with ERC_STRAT_SYNC (corresponding to timing module output  770 ). When the EX CTS is the slave, the ERC generates the external timing reference signal  784  based on the output signal  781  and synchronous with ERC_STRAT_SYNC (corresponding to STRAT_SYNC  755  from the other EX CTS). 
   External reference signal  784  is then sent to a first level clock driver  785  and from there to second level clock drivers  786   a – 786   d  which provide external timing reference signals (STRAT_REF 1 –STRAT_REFN) that are distributed across the mid-plane(s) to EX LTSs on the other network device cards and the EX LTS on the same network device card, the other EX CTS and the EX CTS itself. The ERC circuit also generates BITS 1 _TXREF and BITS 2 _TXREF signals that are provided to BITS T1/E1 framer  758 . 
   The hardware control logic also includes an activity detector  788  that receives STRAT_REF_ACTIVITY from clock driver  785 . Activity detector  788  sends a status signal to the hardware control logic, and if the status indicates that STRAT_REF_ACTIVITY is inactive, then the hardware control logic asserts KILL_CLKTREE. Whenever KILL_CLKTREE is asserted, the activity detector  774   b  in the other EX CTS detects inactivity on STRAT_SYNC and may become the master by selecting the output of the timing module as the input to MUX  772   a.    
   Similar to hardware control logic  684  ( FIGS. 45   a – 45   b ) within the switch fabric CTS, hardware control logic  760  within the EX CTS implements a state machine (similar to the state machine shown in  FIG. 46 ) based on IM_THE_MASTER and YOU_THE_MASTER signals sent between the two EX CTSs and also on slot identification signals (not shown). 
   In one embodiment, ports (e.g.,  571   a – 571   n,    FIG. 49 ) on network device  540  are connected to external optical fibers carrying signals in accordance with the synchronous optical network (SONET) protocol and the external timing reference signal is a 19.44 MHz signal that may be used as the SONET transmit reference clock. This signal may also be divided down to provide an 8 KHz SONET framing pulse (i.e., J0FP) or multiplied up to provide higher frequency signals. For example, four times 19.44 MHz is 77.76 MHz which is the base frequency for a SONET OC1 stream, two times 77.76 MHz provides the base frequency for an OC3 stream and eight times 77.76 MHz provides the base frequency for an OC12 stream. 
   In one embodiment, the embedded processor timing reference signal within the 19.44 Hz external timing reference signal is 8 KHz. Since the processor timing reference signal and the SONET framing pulse are both 8 KHz, the embedded processor timing reference signal may used to supply both. In addition, the embedded processor timing reference signal may also be used to supply BITS 1 _TXREF and BITS 2 _TXREF signals to BITS T1/E1 framer  758 . 
   Referring to  FIG. 51 , the 19.44 Hz external reference timing signal with embedded 8 KHz processor timing reference signal from ERC  782  (i.e., output signal  784 ) includes a duty-cycle distortion  790  every 125 microseconds (us) representing the embedded 8 KHz signal. In this embodiment, VCXO  780  is a 77.76 MHz VCXO providing a 77.76 MHz clock output signal  781 . The ERC uses VCXO output signal  781  to generate output signal  784  as described in more detail below. Basically, every 125 us, the ERC holds the output signal  784  high for one extra 77.76 MHz clock cycle to create a 75%/25% duty cycle in output signal  784 . This duty cycle distortion is used by the EX LTSs and EX CTSs to extract the 8 KHz signal from output signal  784 , and since the EX LTS&#39;s use only the rising edge of the 19.44 Hz signal to synchronize local external timing signals, the duty cycle distortion does not affect that synchronization. 
   External Reference Clock (ERC) circuit: 
   Referring to  FIG. 52 , an embeddor circuit  792  within the ERC receives VCXO output signal  781  (77.76 MHz) at four embedding registers  794   a – 794   d,  a 9720−1 rollover counter  796  and three 8 KHz output registers  798   a – 798   b.  Each embedding register passes its value (logic 1 or 0) to the next embedding register, and embedding register  794   d  provides ERC output signal  784  (19.44 Hz external timing reference signal with embedded 8 KHz processor timing reference signal). The output of embedding register  794   b  is also inverted and provided as an input to embedding register  794   a.  When running, therefore, the embedding registers maintain a repetitive output  784  of a high for two 77.76 MHz clock pulses and then low for two 77.76 MHz which provides a 19.44 Hz signal. Rollover counter  796  and a load circuit  800  are used to embed the 8 KHz signal. 
   The rollover counter increments on each 77.76 MHz clock tick and at 9720−1 (9720−1 times 77.76 MHz=8 KHz), the counter rolls over to zero. Load circuit  800  detects when the counter value is zero and loads a logic 1 into embedding registers  794   a,    794   b  and  794   c  and a logic zero into embedding register  794   d.  As a result, the output of embedding register  794   d  is held high for three 77.76 MHz clock pulses (since logic ones are loaded into three embedding registers) which forces the duty cycle distortion into the 19.44 Hz output signal  784 . 
   BITS circuits  802   a  and  802   b  also monitor the value of the rollover counter. While the value is less than or equal to 4860−1 (half of 8 KHz), the BITS circuits provide a logic one to 8 KHz output registers  798   a  and  798   b,  respectively. When the value changes to 4860, the BITS circuits toggle from a logic one to a logic zero and continue to send a logic zero to 8 KHz output registers  798   a  and  798   b,  respectively, until the rollover counter rolls over. As a result, 8 KHz output registers  798   a  and  798   b  provide 8 KHz signals with a 50% duty cycle on BITS 1 _TXREF and BITS 2 _TXREF to the BITS T1/E1 framer. 
   As long as a clock signal is received over signal  781  (77.76 MHz), rollover counter  796  continues to count causing BITS circuits  802   a  and  802   b  to continue toggling 8 KHz registers  798   a  and  798   b  and causing load circuit  800  to continue to load logic 1110 into the embedding registers every 8 KHz. As a result, the embedding registers will continue to provide a 19 MHz clock signal with an embedded 8 KHz signal on line  784 . This is often referred to as “fly wheeling.” 
   Referring to  FIG. 53 , an extractor circuit  804  within the ERC is used to extract the embedded 8 KHz signal from ERC_STRAT_SYNC. When the EX CTS is the master, ERC_STRAT_SYNC corresponds to the output signal  770  from the timing module  768  (pure 19.44 Hz), and thus, no embedded 8 KHz signal is extracted. When the EX CTS is the slave, ERC_STRAT_SYNC corresponds to the external timing reference signal provided by the other EX CTS (i.e., STRAT_SYNC  755 ; 19.44 Hz with embedded 8 KHz) and the embedded 8 KHz signal is extracted. The extractor circuit includes three extractor registers  806   a – 806   c.  Each extractor register is connected to the 77.76 MHz VCXO output signal  781 , and on each clock pulse, extractor register  806   a  receives a logic one input and passes its value to extractor register  806   b  which passes its value to extractor register  806   c  which provides an 8 KHz pulse  808 . The extractor registers are also connected to ERC_SRAT_SYNC which provides an asynchronous reset to the extractor registers—that is, when ERC_STRAT_SYNC is logic zero, the registers are reset to zero. Every two 77.76 MHz clock pulses, therefore, the extractor registers are reset and for most cycles, extractor register  806   c  passes a logic zero to output signal  808 . However, when the EX CTS is the slave, every 8 KHz ERC_STRAT_SYNC remains a logic one for three 77.76 MHz clock pulses allowing a logic one to be passed through each register and onto output signal  808  to provide an 8 KHz pulse. 
   8 KHz output signal  808  is passed to extractor circuit  804  and used to reset the rollover counter to synchronize the rollover counter to the embedded 8 KHz signal within ERC_STRAT_SYNC when the EX CTS is the slave. As a result, the 8 KHz embedded signal generated by both EX CTSs are synchronized. 
   External Local Timing Subsystem (EX LTS): 
   Referring to  FIGS. 54   a – 54   b , EX LTS  756  receives STRAT_REF_B from one EX CTS and STRAT_REF_A from the other EX CTS. STRAT_REF_B and STRAT_REF_A correspond to one of STRAT_REF 1 –STRAT_REFN ( FIGS. 50   a – 50   c ) output from each EX CTS. STRAT_REF_B and STRAT_REF A are provided as inputs to a MUX  810   a  and a hardware control logic  812  within the EX LTS selects the input to MUX  810   a  using REF_SEL ( 1 : 0 ) signals. An activity detector  814   a  monitors the activity of STRAT_REF_A and sends a signal to hardware control logic  812  if it detects an inactive signal (i.e., stuck at logic one or zero). Similarly, an activity detector  814   b  monitors the activity of STRAT_REF_B and sends a signal to hardware control logic  812  if it detects an inactive signal (i.e., stuck at logic one or zero). If the hardware control logic receives a signal from either activity detector indicating that the monitored signal is inactive, the hardware control logic automatically changes the REF_SEL ( 1 : 0 ) signals to cause MUX  810   a  to select the other input signal and send an interrupt to the local processor. 
   A second MUX  810   b  receives a feed back signal  816  from the EX LTS itself. Hardware control logic  812  uses FB_SEL( 1 : 0 ) to select either a feedback signal input to MUX  810   b  or a test header  818   b  input to MUX  810   b . The test header input is only used in a test mode. In regular use, feedback signal  816  is selected. Similarly, in a test mode, the hardware control logic may use REF_SEL( 1 : 0 ) to select a test header  818   a  input to MUX 810 a.    
   Output signals  820   a  and  820   b  from MUXs  810   a  and 810 b , respectively, are provided to phase detector  822 . The phase detector compares the rising edge of the two input signals to determine the magnitude of any phase shift between the two. The phase detector then generates variable voltage pulses on outputs  821   a  and  821   b  representing the magnitude of the phase shift. The phase detector outputs are used by discrete logic circuit  822  to generate a voltage on signal  823  representing the magnitude of the phase shift. The voltage is used to speed up or slow down (i.e., change the phase of) of an output  825  of a VCXO  824  to track any phase change in STRAT_REF_A or STRAT_REF_B. The discrete logic components implement filters that determine how quickly or slowly the VCXO&#39;s output will track the change in phase detected on the reference signal. 
   In one embodiment, the VCXO is a 155.51 MHz or a 622 MHz VCXO. This value is dependent upon the clock speeds required by components, outside the EX LTS but on the local card, that are responsible for transferring network data over the optical fibers in accordance with the SONET protocol. On at least the universal port card, the VCXO output  825  signal is sent to a clock driver  830  for providing local data transfer components with a 622 MHz or 155.52 MHz clock signal  831 . 
   The VCXO output  825  is also sent to a divider chip  826  for dividing the signal down and outputting a 77.76 MHz output signal  827  to a clock driver chip  828 . Clock driver chip  828  provides 77.76 MHz output signals  829   a  for use by components on the local printed circuit board and provides 77.76 MHz output signal  829   b  to ERC circuit  782 . The ERC circuit also receives input signal  832  corresponding to the EX LTS selected input signal either STRAT_REF_B or STRAT_REF_A. As shown, the same ERC circuit that is used in the EX CTS may be used in the EX LTS to extract an 8 KHz J0FP pulse for use by data transfer components on the local printed circuit board. Alternatively, the ERC circuit could include only a portion of the logic in ERC circuit  782  on the EX CTS. 
   Similar to hardware control logic  712  ( FIGS. 47   a – 47   b ) within the switch fabric LTS, hardware control logic  812  within the EX LTS implements a state machine (similar to the state machine shown in  FIG. 48 ) based on signals from activity detectors  814   a  and  814   b.    
   External Reference Clock (ERC) circuit: 
   Referring again to  FIGS. 52 and 53 , when the ERC circuit is within an EX LTS circuit, the inputs to extractor circuit  804  are input signal  832  corresponding to the LTS selected input signal either STRAT_REF_B or STRAT_REF_A and 77.76 MHz clock input signal  829   b.  The extracted 8 KHz pulse  808  is again provided to embeddor circuit  792  and used to reset rollover counter  796  in order to synchronize the counter with the embedded 8 KHz signal with STRAT_REF_A or STRAT_REF_B. Because the EX CTSs that provide STRAT_REF_A and STRAT_REF_B are synchronous, the embedded 8 KHz signals within both signals are also synchronous. Within the EX LTS, the embedding registers  794   a – 794   d  and BITS registers  798   a  and  798   b  are not used. Instead, a circuit  834  monitors the value of the rollover counter and when the rollover counter rolls over to a value of zero, circuit  834  sends a logic one to 8 KHz register  798   c  which provides an 8 KHz pulse signal  836  that may be sent by the LTS to local data transfer components (i.e., J0FP) and processor components as a local processor timing signal. 
   Again, as long as a clock signal is received over signal  829   b  (77.76 MHz), rollover counter  796  continues to count causing circuit  834  to continue pulsing 8 KHz register  798   c.    
   External Central Timing Subsystem (EX CTS) Alternate Embodiment: 
   Referring to  FIGS. 55   a – 55   c , instead of using one of the STRAT_REF 1 –STRAT_REFN signals from the other EX CTS as an input to MUX  772   a , the output  770  (marked “Alt. Output to other EX CTS”) of timing module  768  may be provided to the other EX CTS and received as input  838  (marked “Alt. Input from other EX CTS”). The PLL circuit, including MUXs  772   a  and 772 b , phase detector  776 , discrete logic circuit  778  and VCXO  780 , is necessary to synchronize the output of the VCXO with either output  770  of the timing module or a signal from the other EX CTS. However, PLL circuits may introduce jitter into their output signals (e.g., output  781 ), and passing the PLL output signal  781  via one of the STRAT_REF 1 –STRAT_REFN signals from one EX CTS into the PLL of the other EX CTS—that is, PLL to PLL—may introduce additional jitter into output signal  781 . Since accurate timing signals are critical for proper data transfer with other network devices and SONET standards specifically set maximum allowable jitter transmission at interfaces (Bellcore GR-253-CORE and SONET Transport Systems Common Carrier Criteria), jitter should be minimized. Passing the output  770  of the timing module within the EX CTS to the input  838  of the other EX CTS avoids passing the output of one PLL to the input of the second PLL and thereby reduces the potential introduction of jitter. 
   It is still necessary to send one of the STRAT_REF 1 –STRAT_REFN signals to the other EX CTS (received as STRAT_SYNC  755 ) in order to provide ERC  782  with a 19.44 Hz signal with an embedded 8 KHz clock for use when the EX CTS is a slave. The ERC circuit only uses ERC_STRAT_SYNC in this instance when the EX CTS is the slave. 
   Layer One Test Port: 
   The present invention provides programmable physical layer (i.e., layer one) test ports within an upper layer network device (e.g., network device  540 ,  FIGS. 35   a – 35   b ). The test ports may be connected to external test equipment (e.g., an analyzer) to passively monitor data being received by and transmitted from the network device or to actively drive data to the network device. Importantly, data provided at a test port accurately reflects data received by or transmitted by the network device with minimal modification and no upper layer translation or processing. Moreover, data is supplied to the test ports without disrupting or slowing the service provided by the network device. 
   Referring to  FIGS. 35   a – 35   b  and  36   a – 36   b , network device  540  includes at least one cross-connection card  562   a – 562   b,    564   a – 564   b,    566   a – 566   b,    568   a – 568   b,  at least one universal port card  554   a – 554   h,    556   a – 556   h,    558   a – 558   h,    560   a – 560   h,  and at least one forwarding card  546   a – 546   e,    548   a – 548   e,    550   a – 550   e,    552   a – 552   e.  Each port card includes at least one port  571   a – 571   n  for connecting to external physical network attachments  576   a – 576   b,  and each port card transfers data to a cross-connection card. The cross-connection card transfers data between port cards and forwarding cards and between port cards. In one embodiment, each forwarding card includes at least one port/payload extractor  582   a – 582   n  for receiving data from the cross-connection cards. 
   Referring to  FIG. 56 , a port  571   a  on a port card  554   a  within network device  540  may be connected to another network device (not shown) through physical external network attachments  576   a  and  576   b.  As described above, components  573  on the port card transfer data between port  571   a  and cross-connection card  562   a,  and components  563  on the cross-connection card transfer data on particular paths between the port cards and the forwarding cards or between port cards. For convenience, only one port card, forwarding card and cross-connection card are shown. 
   For many reasons, including error diagnosis, a service administrator may wish to monitor the data received on a particular path or paths at a particular port, for example, port  571   a,  and/or the data transmitted on a particular path or paths from port  571   a.  To accomplish this, the network administrator may connect test equipment, for example, an analyzer  840  (e.g., an Orniber analyzer available from Hewlett Packard Company), to the transmit connection of port  571   b  to monitor data received at port  571   a  and/or to the transmit connection of port  571   c  to monitor data transmitted from port  571   a.  The network administrator then notifies the NMS (e.g., NMS  60  running on PC  62 ,  FIGS. 35   a – 35   b ) as to which port or ports on which port card or port cards should be enabled and whether the transmitter and/or receiver for each port should be enabled. The network administrator also notifies the NMS as to which path or paths are to be sent to each test port, and the time slot for each path. With this information, the NMS fills in test path table  841  ( FIGS. 57 and 58 ) in configuration database  42 . 
   Similar to the process of enabling a working port through path table  600  ( FIGS. 37 and 38 ), when a record in the test path table is filled in, the configuration database sends an active query notification to the path manager (e.g., path manager  597 ) executing on the universal port card (e.g., port card  554   a ) corresponding to the universal port card port LID in the path table record. For example, port  571   b  may have a port LID of  1232  (record  842 ,  FIG. 58 ) and port  571   b  may have a port LID of  1233  (record  843 ). An active query notification is also sent to NMS database  61 , and once the NMS database is updated, the NMS displays the new system configuration, including the test ports, to the user. 
   Through the test path table, the path manager learns that the transmitters of ports  571   b  and  571   c  need to be enabled and which path or paths are to be transferred to each port. As shown in path table  600  ( FIG. 38 ), path LID  1666  corresponds to working port LID  1231  (port  571   a ), and as shown in test path table  841  ( FIG. 58 ), path LID  1666  is also assigned to test port LIDs  1232  and  1233  (ports  571   b  and  571   c,  respectively). Record  842  indicates that the receive portion of path  1666  (i.e., “ingress” in Monitor column  844 ) is to be sent to port LID  1232  (i.e., port  571   b ) and then transmitted (i.e., “no” in Enable Port Receiver column  845 ) from port LID  1232 , and similarly, record  843  indicates that the transmit portion of path  1666  (i.e., “egress” in Monitor column  844 ) is to be sent to port LID  1233  (i.e., port  571   c ) and then transmitted (i.e., “no” in Enable Port Receiver column  845 ) from port LID  1233 . 
   The path manager passes the path connection information to cross-connection manager  605  executing on the cross-connection card  562   a.  The CCM uses the connection information to generate a new connection program table  601  and uses this table to program internal connections through one or more components (e.g., a TSE chip  563 ) on the cross-connection card. After re-programming, cross-connection card  562   a  continues to transmit data corresponding to path LID  1666  between port  571   a  on universal port card  554   a  and the serial line input to payload extractor  582   a  on forwarding card  546   c.  However, after reprogramming, cross-connection card  562   a  also multicasts the data corresponding to path LID  1666  and received on port  571   a  to port  571   b  and data corresponding to path LID  1666  and transmitted to port  571   a  by forwarding card  546   c  to port  571   c.    
   Analyzer  840  may then be used to monitor both the network data received on port  571   a  and the network data being transmitted from port  571   a.  Alternatively, analyzer  840  may only be connected to one test port to monitor either the data received on port  571   a  or the data transmitted from port  571   a.  The data received on port  571   a  may be altered by the components on the port card(s) and the cross-connection cards before the data reaches the test port but any modification is minimal. For example, where the external network attachment  576   a  is a SONET optical fiber, the port card components may convert the optical signals into electrical signals that are passed to the cross-connection card and then back to the test ports, which reconvert the electrical signals into optical signals before the signals are passed to analyzer  840 . Since the data received at port  571   a  has not been processed or translated by the upper layer processing components on the forwarding card, the data accurately reflects the data received at the port. For example, the physical layer (e.g., SONET) information and format is accurately reflected in the data received. 
   To passively monitor both the data received and transmitted by a particular port, two transmitters are necessary and, thus, two ports are consumed for testing and cannot be used for normal data transfer. Because the test ports are programmable through the cross-connection card, however, the test ports may be re-programmed at any time to be used for normal data transfer. In addition, redundant ports may be used as test ports to avoid consuming ports needed for normal data transfer. Current network devices often have a dedicated test port that can provide both the data received and transmitted by a working port. The dedicated test port, however, contains specialized hardware that is different from the working ports and, thus, cannot be used as a working port. Hence, although two ports may be consumed for monitoring the input and output of one working port, they are only temporarily consumed and may be re-programmed at any time. Similarly, if the port card on which a test port is located fails, the test port(s) may be quickly and easily reprogrammed to another port on another port card that has not failed. 
   Instead of passively monitoring the data received at port  571   a,  test equipment  840  may be connected to the receiver of a test port and used to drive data to network device  540 . For example, the network administrator may connect test equipment  840  to the receiver of test port  571   c  and then notify the NMS to enable the receiver on port  571   c  to receive path  1666 . With this information, the NMS modifies test path table  841 . For example, record  844  ( FIG. 58 ) indicates that the receive portion of path  1666  (i.e., “ingress” in Monitor column  844 ) is to be driven (i.e., “yes” in Enable Port Receiver column  845 ) externally with data from port LID  1233  (i.e., port  571   c ). Again, an active query notification is sent to path manager  597 . Path manager  597  then disables the receiver corresponding to port LID  1231  (i.e., port  571   a ) and enables the receiver corresponding to port LID  1233  (i.e., port  571   c ) and passes the path connection information to cross-connection manager  605  indicating that port LID  1231  will supply the receive portion of path  1666 . The cross-connection manager uses the connection information to generate a new connection program table  601  to re-program the internal connections through the cross-connection card. In addition, the network administrator may also indicate that the transmitter of port  571   a  should be disabled, and path manager  597  would disable the transmitter of port  571   a  and pass the connection information to the cross connection manager. 
   After reprogramming, cross-connection card  562   a  data is sent from test equipment  840  to test port  571   c  and then through the cross-connection card to forwarding card  546   c.  The cross-connection card may multicast the data from forwarding card  546   c  to both working port  571   a  and to test port  571   c,  or just to test port  571   c  or just working port  571   a.    
   Instead of having test equipment  840  drive data to the network device over a test port, internal components on a port card, cross-connection card or forwarding card within the network device may drive data to the other cards and to other network devices over external physical attachments connected to working ports and/or test ports. For example, the internal components may be capable of generating a pseudo-random bit sequence (PRBS). Test equipment  840  connected to one or more test ports may then be used to passively monitor the data sent from and/or received by the working port, and the internal components may be capable of detecting a PRBS over the working port and/or test port(s). 
   Although the test ports have been shown on the same port card as the working port being tested, it should be understood, that the test ports may be on any port card in the same quadrant as the working port. Where cross-connection cards are interconnected, the test ports may be on any port card in a different quadrant so long as the cross-connection card in the different quadrant is connected to the cross-connection card in same quadrant as the working port. Similarly, the test ports may be located on different port cards with respect to each other. A different working port may be tested by re-programming the cross-connection card to multicast data corresponding to the different working port to the test port(s). In addition, multiple working ports may be tested simultaneously by re-programming the cross-connection card to multicast data from different paths on different working ports to the same test port(s) or to multiple different test ports. A network administrator may choose to dedicate certain ports as test ports prior to any testing needing to be done or the network administrator may choose certain ports as test ports when problems arise. 
   The programmable physical layer test port or ports allow a network administrator to test data received at or transmitted from any working port or ports and also to drive data to any upper layer card (i.e., forwarding card) within the network device. Only the port card(s) and cross-connection card need be working properly to passively monitor data received at and sent from a working port. Testing and re-programming test ports may take place during normal operation without disrupting data transfer through the network device to allow for diagnosis without network device disruption. 
   NMS Server Scalability 
   As described above, a network device (e.g.,  10 ,  FIG. 1 and 540 ,  FIGS. 35   a – 35   b ) may include a large number (e.g., millions) of configurable/manageable objects. Manageable objects are typically considered physical or logical. Physical managed objects correspond to the physical components of the network device such as the network device itself, one or more chassis within the network device, shelves in each chassis, slots in each shelf, cards inserted in each slot, physical ports on particular cards (e.g., universal port cards), etc. Logical managed objects correspond to configured elements of the network device such as SONET paths, internal logical ports (e.g., forwarding card ports), ATM interfaces, virtual ATM interfaces, virtual connections, paths/interfaces related to other network protocols (e.g., MPLS, IP, Frame Relay, Ethernet), etc. 
   If multiple NMS clients request access to multiple different network devices and the NMS server is required to retrieve and store data for all managed objects corresponding to each network device, then the NMS server&#39;s local memory will likely be quickly filled and repeated retrievals of data from each network device will likely be necessary. Retrieval of a large amount of data from each network device limits the scalability of the NMS server and reduces the NMS server&#39;s response time to NMS client requests. 
   To improve the scalability of the NMS server and improve data request response times, only physical managed objects are initially retrieved from a selected network device and logical managed objects are retrieved only when necessary. To further increase NMS server scalability and response time, proxies for managed objects (preferably physical managed objects and only a limited number of global logical managed objects) are stored in memory local to each NMS client. Moreover, to increase NMS server scalability and response time, unique identification numbers corresponding to each managed object are also stored in memory local to the NMS client (for example, in proxies or GUI tables) and used by the NMS server to quickly retrieve data requested by the NMS client. Each NMS client, therefore, maintains its user context of interest, eliminating the need for client-specific device context management by the NMS server. 
   Referring to  FIG. 59 , an NMS client  850   a  runs on a personal computer or workstation  984  and uses data in graphical user interface (GUI) tables  985  stored in local memory  986  to display a GUI to a user (e.g., network administrator, provisioner, customer) after the user has logged in. In one embodiment, the GUI is GUI  895  described above with reference to  FIGS. 4   a – 4   z,    5   a – 5   z,    6   a – 6   p,    7   a – 7   y,    8   a – 8   e,    9   a – 9   n,    10   a – 10   i  and  11   a – 11   h.  When GUI  895  is initially displayed (see  FIG. 4   a ), only navigation tree  898  is displayed and under Device branch  898   a  a list  898   b  of IP addresses and/or domain name server (DNS) names may be displayed corresponding to network devices that may be managed by the user in accordance with the user&#39;s profile. 
   If the user selects one of the IP addresses (e.g., 192.168.9.202,  FIG. 4   f ) in list  898   b,  then the client checks local memory  986  ( FIG. 59 ) for proxies (described below) corresponding to the selected network device and if such proxies are not in local memory  986 , the NMS client sends a network device access request including the IP address of the selected network device to an NMS server, for example, NMS server  851   a.  The NMS server may be executed on the same computer or workstation as the client or, more likely, on a separate computer  987 . The NMS server checks local memory  987   a  for managed objects corresponding to the network device to be accessed and if the managed objects are not in local memory  987   a,  the NMS server sends database access commands to the configuration database  42  within the network device corresponding to the IP address sent by the NMS client. The database access commands retrieve only data corresponding to physical components of the network device. 
   In one embodiment, data is stored within configuration database  42  as a series of containers. Since the configuration database is a relational database, data is stored in tables and containment is accomplished using pointers from lower level tables (children) to upper level tables (parents). As previously discussed with reference to  FIGS. 12   a – 12   c,  after the network device is powered-up, the Master MCD (Master Control Driver)  38  takes a physical inventory of the network device (e.g., computer system  10 ,  FIG. 1 , network device  540 ,  FIGS. 35   a – 35   b ,  59 ) and assigns a unique physical identification number (PID) to each physical component within the system, including the network device itself, each chassis in the network device, each shelf in each chassis, each slot in each shelf, each card inserted in each slot, and each port on each card having a physical port (e.g., universal port cards). As previously stated, the PID is a unique logical number unrelated to any physical aspect of the component. 
   The MCD then fills in tables for each type of physical component, such tables being provided by a default configuration within the configuration database. Alternatively, the MCD could create and fill in each table. In one embodiment, the configuration database includes a managed device table  983  ( FIG. 60   a ), a chassis table  988  ( FIG. 60   b ), a shelf table  989  ( FIG. 60   c ), a slot table  990  ( FIG. 60   d ), a card table  47 ′ ( FIG. 60   e ), and a port table  49 ′ ( FIG. 60   f ). The MCD enters the assigned unique PID for each physical component in a row (i.e., record) in one of the tables. Consequently, each unique PID serves as a primary key within the configuration database for the row/data corresponding to each physical component. Where available, the MCD also enters data representing attributes (e.g., card type, port type, relative location, version number, etc.) for the component in each table row. In addition, with the exception of the managed device table, each row includes a unique PID corresponding to a parent table. The unique PID corresponding to a parent table is a pointer and provides data “containment” by linking each child table to its parent table (i.e., provides a table hierarchy). The unique PID corresponding to the parent table may also be referred to as a foreign key for association. 
   Referring to  FIG. 60   a,  since the managed device is the top physical level, managed device table  983  includes one row  983   a  representing the one managed device (e.g.,  540 ,  FIGS. 35   a – 35   b  and  59 ) including a unique managed device PID  983   b  (e.g., 1; i.e., primary key) and attributes A 1 –An corresponding to the managed device but the managed device table does not include a parent PID (i.e., foreign key for association). In the current embodiment, chassis table  988  includes one row  988   a  representing the one chassis (e.g.,  620 ,  FIGS. 41   a – 41   b ) in the managed device. Other network devices may have multiple chassis and a row would be added to the chassis table for each chassis and each row would include the same managed device PID (e.g., 1). Each row in the chassis table includes a unique chassis PID  988   b  (e.g., 2; i.e., primary key) and attributes A 1 –An corresponding to the chassis and a managed device PID  988   c  (i.e., parent PID/foreign key for association). Referring to  FIG. 60   c,  shelf table  989  includes one row for each shelf in the chassis and each row includes a unique shelf PID  989   a  (e.g., 3–18; i.e., primary key) and attributes A 1 –An corresponding to each shelf and a chassis PID  989   b  (i.e., foreign key for association). Since all the shelves are in the same chassis in this embodiment, they each list the same chassis PID (e.g., 2). Referring to  FIG. 60   d,  slot table  990  includes one row for each slot in the chassis and each row includes a unique slot PID  990   a  (e.g.,  20 – 116 ; i.e., primary key) and attributes A 1 –An corresponding to each slot and a shelf PID  990   b  (i.e., foreign key for association). Since there may be many shelves in the chassis, the shelf PID in each row corresponds to the shelf in which the slot is located. For example, a row  990   c  includes slot PID  20  corresponding to a shelf PID of 3, and a row  990   d  includes slot PID  116  corresponding to a different shelf PID of 18. 
   Referring to  FIG. 60   e,  card table  47 ′ includes one row for each card inserted within a slot in the chassis and each row includes a unique card PID  47   a  (i.e., primary key), attributes (e.g., CWD Type, Version No., etc.) corresponding to each card and a slot PID  47   b  (i.e., foreign key for association) corresponding to the slot in which the card is inserted. Referring to  FIG. 60   f,  port table  49 ′ includes one row for each physical port located on a universal port card in the chassis and each row includes a unique port PID  49   a  (i.e., primary key), attributes (e.g., port type, version no., etc.) corresponding to each port and a card PID  49   b  (i.e., foreign key for association) corresponding to the card on which the port is located. 
   Even after initial power-up, master MCD  38  continues to take physical inventories of the network device to determine if physical components have been added or removed. For example, cards may be added to empty slots or removed from slots. When changes are detected, master MCD  38  updates the tables (e.g., card table  47 ′ and port table  49 ′) accordingly, and through the active query feature, the configuration database updates an external NMS database (e.g.,  61 ,  FIG. 59 ) and notifies the NMS server. In one embodiment, each time a physical component is changed, the NMS server sends the NMS client a full set of updated proxies to ensure that the NMS client is fully synchronized with the network device. Alternatively, only those proxies that are affected may be updated. As described below, however, proxies may include pointers to both a parent proxy and children proxies, and if so, even a change to only one physical component requires changes to the proxy for that component and any related parent and/or children proxies. 
   In this embodiment, therefore, when the server sends database access commands to the configuration database within the network device to retrieve all data corresponding to physical components of the network device, the database access commands request data from each row in each of the physical tables (e.g., managed device table  983 , chassis table  988 , shelf table  989 , slot table  990 , card table  47 ′ and port table  49 ′). The data from these tables is then sent to the NMS server, and the server creates physical managed objects (PMO 1 –PMOn,  FIG. 59 ) for each row in each table and stores them in local memory  987   a.    
   Referring to  FIG. 61   a,  each physical managed object  991  created by the NMS server includes the unique PID  991   a  and the attribute data  991   b  associated with the particular row/record in the configuration database table and function calls  991   c.  With the exception of the managed device physical managed object, the attribute data includes a pointer (i.e., PID) for the corresponding parent physical component, and with the exception of the port physical managed objects, each managed object&#39;s attribute data also includes one or more pointers (i.e., PIDs) corresponding to any children physical components. In this embodiment, the port managed objects are the lowest level physical component and, therefore, do not include pointers to children physical components. 
   In one embodiment, all physical managed objects include a “Get Parent”  991   e  function call to cause the NMS server to retrieve data corresponding to the parent physical component. A Get Parent function call to the managed device managed object receives a null message since the managed device does not have a parent component. The Get Parent function call may be used for constraint checking. For example, prior to configuring a particular card as a backup for another card, the Get Parent function call may be placed twice by the NMS server to ensure that both cards are within the same shelf—that is, the network device may have a constraint that redundant boards must be within the same shelf. The first Get Parent function call determines which slot each card is in and the second Get Parent function call determines which shelf each slot is in. If the shelves match, then the constraint is met. 
   In one embodiment, all physical managed objects include a “Get Children”  991   f  function call to cause the NMS server to retrieve data from the configuration database for children physical components related to the physical managed object. A Get Children function call to a port managed object receives a null message since the port does not have any physical children components. The data retrieved with the Get Children function call is used to fill in the tables in the physical tabs (e.g., system tab  934  ( FIG. 4   s ), module tab  936  ( FIG. 4   t ), ports tab  938  ( FIG. 4   u ) and SONET Interfaces tab  940  ( FIG. 4   v )) within configuration/status window  897  ( FIG. 5   q ). Some or all of the data from each row in the configuration database tables may be used to fill in these tables. 
   In addition to Get Children and Get Parent function calls, each physical managed object includes a “Get Config”  991   g  and a “Set Config”  991   h  function call. The Get Config function call is used to retrieve data for dialog boxes when a user double clicks the left mouse button on an entry in one of the tabs in status window  897 . The Set Config function call is used to implement changes to managed objects received from a user through a dialog box. 
   Instead of a “Get Children” function call, the port managed object includes a “Get SONET Path Table” function call to cause the server to retrieve all SONET paths (logical managed objects) configured for that particular port for display in SONET Paths tab  942  ( FIG. 5   q ). Since SONET paths are children to a port, the “Get SONET Path Table” corresponds to the “Get Children” function call in the other physical managed objects. However, the pointers (i.e., logical identification numbers (LIDs)) to the children are not stored in the port managed object attribute data. This is because the number of SONET paths that the SONET port would need to point may be large and would have to be regularly updated as SONET Paths are created and deleted. The port managed object also includes a “Create SONET Path” function call and a “Delete SONET Path” function call to cause the server to create or delete, respectively, a SONET path for that particular port. As described below, the port managed object may also include other function calls related to logical components. 
   Each managed object  991  also includes a “Get Proxy” function call  991   d,  and after creating each managed object, the NMS server places a get proxy function call to the managed object. Placing the get proxy call causes the NMS server to create a proxy (PX) for the managed object and send the proxy (e.g., PX 1 –PXn) to memory  986  local to the NMS client that requested the network device access. Referring to  FIG. 61   b,  each proxy includes the PID  992   a  and some or all of the attribute data  992   b  from the corresponding managed object. The decision to include some or all of the attribute data within the proxy may depend upon the size of the memory  986  local to the NMS client. This may be a static design decision based on the expected size of the memory local to the typical NMS client, or this may be a dynamic decision based on the actual size of the memory local to the NMS client that requested access to the network device. If sufficiently large, the proxy may include all the attribute data. If not sufficiently large, then perhaps only attribute data regularly accessed by users may be included in the proxy. For example, for a port managed object perhaps only the port name, connection type and relative position within the network device is included in the proxy. 
   In addition, each proxy may include function calls  992   c  similar to one or more function calls in the corresponding managed object, with the exception of the “Get Proxy” function call. Unlike the managed object function calls, however, the proxy function calls cause the NMS client to send messages to the NMS server in, for example, JAVA RMI. For instance, the SONET Port proxy like the SONET Port managed object includes the “Get SONET Path Table”, “Create SONET Paths” and “Delete SONET Paths” function calls. However, proxy function calls cause the NMS client to send JAVA RMI messages to the NMS server to cause the server to place similar function calls to the managed object. The managed object function calls cause the server to generate database access commands to the configuration database in the network device. 
   Initially, the NMS client uses data from the received proxies (PX 1 –PXn,  FIG. 59 ) to update GUI tables  985  which causes the GUI to display device mimic  896   a  ( FIG. 4   f ) in graphic window  896   b  and system tab  934  ( FIG. 4   s ) in configuration/service status window  897 . Limiting the initial data retrieval from the configuration database to only data corresponding to physical components of the network device—as opposed to both physical and logical components—reduces the amount of time required to transfer the data from the configuration database to the NMS server and on to the NMS client. Thus, the NMS client is able to display the device mimic and system tab more quickly than if data corresponding to both the physical and logical components were retrieved. To further increase the speed with which the device mimic and system tab are displayed, the NMS server may first transfer the proxies necessary for the device mimic and the system tab and then transfer the proxies corresponding to other physical tabs, including module (i.e., card) tab  936  ( FIG. 4   t ), port tab  938  ( FIG. 4   u ) and SONET Interfaces tab  940  ( FIG. 4   v ). 
   If a user selects a different network device from navigation tree  898  ( FIG. 5   h ) using NMS client  850   a,  NMS client  850   a  searches local memory  986  for proxies associated with the selected network device and if not found, the NMS client sends JAVA RMI messages to the NMS server to cause the NMS server to retrieve all physical data from the selected network device, create physical managed objects, store them in local memory  987   a,  create proxies for each physical managed object and send the proxies to the NMS client. If memory  986  local to the NMS client is sufficiently large, then the proxies for the first selected network device may remain in memory along with the proxies for the second selected network device. Consequently, if the user re-selects the first selected network device, the proxies are located in local memory by the NMS client, and the NMS client does not have to access the NMS server. 
   In addition to reducing the time required to display physical information through GUI  895 , limiting the initial data retrieval to only physical data reduces the amount of memory  987   a  local to the NMS server required to store the managed objects. Moreover, once the data from the proxies are added to the GUI tables, the GUI can respond to a user request for any of the device views within the mimic (as shown in  FIGS. 4   f – 4   r ) and to a user request for any physical tab without having to send data requests to the NMS server. Consequently, the GUI response time is increased, traffic between the NMS client and server is reduced and the burden on the server to respond to client requests is reduced. 
   If the proxies include all of the attribute data from the managed objects, then once the proxies are transferred to the NMS client, it is not necessary for the NMS server to continue storing the corresponding physical managed objects. If, however, a proxy includes only some of the attribute data from its corresponding managed object, then continuing to store the managed object at the NMS server saves time if the user requests access to data not included in the proxy. For example, a proxy may only include data for attributes displayed in a tab in status window  897 . If a user desires more data, the user may double click the left mouse button on an entry in the tab to cause a dialog box to be displayed including additional attribute data. This causes the NMS client to place a Get Config function call to the corresponding proxy which causes the NMS client to send JAVA RMI messages to the NMS server. If the managed object is still in local memory  987   a,  then the response time to the client is faster than if the server needs to access the configuration database again to retrieve the data. 
   Maintaining the managed objects for a particular network device in local memory  987   a  is also advantageous if another NMS client requests access to the same network device. As previously mentioned, when the NMS server receives a network device access request, it first checks local memory  987   a.  If the managed objects are already present, then the NMS server may respond more quickly than if the server again needs to retrieve the data from the network device. 
   Due to the advantages described above, in one embodiment, the NMS server does not automatically delete managed objects from its local memory after proxies are sent to the NMS client. However, because the NMS server&#39;s local memory is a limited resource, as clients request access to more and more different network devices, it may become necessary for the NMS server to overwrite managed objects within local memory  987   a  such that they are no longer available. As previously mentioned, sending proxies to the NMS clients allows the clients to display physical data through GUI  895  without accessing the NMS server. Thus, even when the NMS server is forced to overwrite corresponding managed objects in local memory  987   a,  the client is able to continue displaying physical data through GUI  895 . 
   Importantly, through the unique PID and the function calls, the proxies also provide an improved mechanism for accessing logical data and physical data not included within the proxies. As mentioned above, if the user requests access to physical data not in the proxy, then the NMS client places a Get Config function call to the NMS server. The function call is made more efficient by including the unique PID stored in the proxy. The NMS server uses the PID to first search local memory  987   a —perhaps the NMS server searches a hash table in cache. If the PID is found, then the NMS quickly sends the data from the corresponding managed object to the NMS client. If the PID is not found in local memory  987   a,  then the NMS server uses the PID as a primary key to retrieve the physical data from the configuration database within the network device and again builds the corresponding physical managed object. The NMS server then sends the data from the managed object to the NMS client. 
   Without the PID, the NMS server would be forced to walk through the hierarchical physical tables until the correct physical component was found. For example, if the NMS server needs data relevant to a particular port, the NMS server would begin by locating the managed device, the chassis, then the correct shelf within the chassis, then the correct slot within the chassis, then the module within the slot and then finally the correct port on the module. This will likely take several database accesses and will certainly take more time than directly accessing the port data using a primary key that provides absolute context. 
   The process is similar if the data requested is logical. For example, if a user selects a particular port (e.g., port  939   a,    FIG. 5   a ) and then selects SONET Paths tab  942  ( FIG. 5   h ), the logical data associated with the SONET paths configured for the selected port (e.g., SONET paths  942   a  and  942   b ) is needed. To do this, the NMS client places a “Get SONET Path Table” function call to the port proxy which causes the NMS client to issue JAVA RMI messages to the NMS server including a request for the SONET paths configured for the physical port associated with the unique port PID stored in the proxy. The NMS server first searches local memory  987   a  for the PID. If a managed object including the PID is found in local memory, then the NMS server places a similar “Get SONET Path Table” function call through the port managed object. If the PID is not found in local memory, then the NMS server uses the port PID as a primary key to quickly retrieve the data from the configuration database stored in the table row corresponding to the selected port. The NMS server again builds the managed object for the port and then places the “Get SONET Path Table” function call through the managed object. The Get SONET Path Table function call within the managed object causes the NMS server to generate database access commands to the configuration database within the network device to retrieve data corresponding to each SONET path configured for the selected port. Only some of the data in each row may be necessary to fill in the fields in the tab (e.g., SONET Paths tab  942 ,  FIG. 4   w ). 
   Similar to the physical data, logical data is stored in tables within configuration database  42  ( FIG. 59 ). The tables may be provided as part of a default configuration within the configuration database, or the tables may be created within the configuration database as each different type of table is needed. In one embodiment, configuration database  42  includes a SONET Path Table (e.g.,  600 ′,  FIG. 60   g ), a Service End Point Table (e.g.,  76 ″,  FIG. 60   h ), an ATM Interface Table (e.g.,  114 ″,  FIG. 60   i ), a Virtual ATM Interface Table (e.g.,  993 ,  FIG. 60   j ), a Virtual Connection Table (e.g.,  994 ,  FIG. 60   k ), a Virtual Link Table (e.g.,  995 ,  FIG. 60   l ) and a Cross-Connect Table (e.g.,  996 ,  FIG. 60   m ). Tables corresponding to other physical layer or upper layer network protocols may also be included within configuration database  42 . 
   The database access commands corresponding to the Get SONET Path Table function call include the port PID (from the proxy/JAVA RMI messages) associated with the selected port. When the database access commands corresponding to the Get SONET Path Table function call are received by the configuration database, the configuration database locates each row in SONET Path Table  600 ′ ( FIG. 60   g ) including the selected port PID and returns to the NMS server the data from each row necessary for the SONET Paths tab. Thus, the retrieved data is limited to those rows/records corresponding to the selected port and the data necessary for the tab. This allows the NMS server and NMS client to quickly respond to the user&#39;s request for logical data. If all SONET paths configured for all SONET ports within the network device (or worse, all logical data) were retrieved, then the response time would likely be much slower. 
   For each row of data the NMS server formats the data according to the SONET Paths tab display and sends it to the NMS client. The NMS client adds the data to the GUI tables which causes the GUI tables to display the SONET paths (e.g.,  942   a  and  942   b,    FIG. 5   h ) configured for the selected port. Along with the data necessary for the SONET Paths tab, the NMS server also sends the LID for each logical managed object (i.e., each SONET path) and the NMS client saves the LID within the GUI tables, in one embodiment, within a column hidden from the user. 
   As previously discussed, to retrieve additional attribute data or change attribute data for a managed object, the user may simply double click the left mouse button on an entry in a tab in configuration/status window  897  ( FIG. 5   q ) to cause a dialog box to appear. When the user double clicks the left mouse button on the entry, the NMS client places a “Get Config” function call to the corresponding proxy and simultaneously opens a GUI dialog  998  ( FIG. 59 ) in local memory  986 . If the selected entry is for a physical component of the network device, then the function call causes the NMS client to populate GUI dialog  998  with attribute data from the proxy. If the selected entry is for a logical component of the network device, for example, a SONET path, then the NMS client needs data from the configuration database within the network device to populate GUI dialog  998 . 
   For example, if a user selects SONET path  942   a  ( FIG. 5   q ) from SONET Paths tab  942  and double clicks the left mouse button, the NMS client displays a SONET Path dialog box  997  ( FIG. 62 ). To do this, when the user double clicks the left mouse button on the entry, the NMS client places a “Get Config” function call to the corresponding port proxy and simultaneously opens a GUI dialog  998  ( FIG. 59 ) in local memory  986 . The function call causes the NMS client to send JAVA RMI messages to the NMS server including both the port PID from the proxy and the SONET path LID from the GUI table. The NMS server first searches local memory  987   a  for the port PID. If a managed object including the port PID is found, then the NMS server issues a “Get Config” function call to the managed object including the SONET Path LID. If the port PID is not found, then the NMS server uses the port PID as a primary key into the configuration database to retrieve data from the row/record corresponding to the port. The NMS server then creates the port managed object, stores it in local memory and issues the “Get Config” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to retrieve all the attribute data in the row in SONET Path Table  600 ′ ( FIG. 60   g ) corresponding to the SONET path LID. The server uses the retrieved data to build a configuration object and sends the configuration object to the NMS client. The NMS client then uses the configuration object to populate GUI dialog  998  with the data which causes the dialog box  997  ( FIG. 62 ) to display the data to the user. 
   If the user then selects a Cancel button  997   a  or OK button  997   b,  then the NMS client closes the dialog box. If the user selects Cancel button  997   a,  then the NMS client closes and deletes GUI dialog  998  and takes no further action. If the user selects OK button  997   b,  then it is assumed that the user made changes to one or more SONET path attributes and now wants those changes implemented. To implement any changes made to the SONET path attributes, when the NMS client detects the selection of the OK button, the NMS client places a “Set Config” function call to the corresponding port proxy. The function call causes the NMS client to send JAVA RMI messages to the NMS server including both the port PID from the proxy and the SONET path LID from the GUI table and the attributes for the SONET path. The NMS server first searches local memory  987   a  for the port PID. If a managed object including the port PID is found, then the NMS server issues a “Set Config” function call to the managed object including the SONET Path LID. If the port PID is not found, then the NMS server uses the port PID as a primary key into the configuration database to retrieve data from the row/record corresponding to the port. The NMS server then creates the port managed object, stores it in local memory and issues the “Set Config” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to locate the row in SONET Path Table  600 ′ ( FIG. 60   g ) corresponding to the SONET path LID and replace the attributes in that row with the attributes included in the database access commands. As discussed in detail above, when tables in the configuration database are updated an active query feature is used to notify other processes of the changes. For example, NMS database  61  ( FIG. 59 ) is automatically updated with any changes. NMS database  61  may be located within computer/workstation  987  or  984  or within a separate computer/workstation  997 . In addition, the changes are sent to the NMS server which uses the data to re-build the configuration object. The NMS server then sends the configuration object to the NMS client. The NMS client uses the configuration object as an indication that the Set Config function call was successful. The NMS client then closes and deletes GUI dialog  998  and uses the received data to update the GUI tables  985 . 
   Alternatively, proxies may be created for each logical managed object and sent to the NMS client. In a typical network device, however, there may be millions of logical managed objects making storage of all logical proxies in memory local to an NMS client difficult if not impossible. Moreover, since logical managed objects change frequently (as opposed to physical managed objects which do not change as frequently), the stored logical proxies would need to be updated frequently leading to an increased burden on both the NMS server and NMS client. Thus, in the preferred embodiment, only physical proxies are created and stored local to the NMS client. 
   Using the unique PIDs as primary keys allows for faster response times by the NMS server. First the PIDs are used to quickly check local memory  987   a —perhaps hash tables in a cache. If the data is not in local memory, the PIDS are used as primary keys to perform a fast data retrieval from configuration database  42 . If the PIDs were not used, the NMS server would need to navigate through the hierarchy of tables—possibly performing multiple database accesses—to locate the data of interest and, thus, response time would be much slower. As primary keys, the PIDs allow the NMS server to directly retrieve required data (i.e., table rows/records) without having to navigate through upper level tables. 
   Since logical data corresponds to configured objects, rows are added to the tables when logical objects are configured. In addition, the NMS server assigns a unique logical identification number (LID) for each configured object and inserts this within each corresponding row. The LID, like the PID, is used as a primary key within the configuration database for the row/data corresponding to each logical component. The NMS server and MCD use the same numbering space for LIDs, PIDs and other assigned numbers to ensure that the numbers are different (no collisions). In each row, the NMS server also inserts a unique PID or LID corresponding to a parent table (i.e., a foreign key for association) to provide data “containment”. 
   As described above with reference to  FIGS. 5   a – 5   p,  a user may select a port or a SONET interface and then access a SONET path configuration wizard to configure SONET paths on the selected port/interface. When the user selects OK button  944   r,  the NMS client places a “Create SONET Path” function call to the proxy corresponding to the selected port/interface including the port PID in the proxy and the parameters provided by the user through the SONET path configuration wizard. The function call causes the NMS client to send JAVA/RMI messages to the NMS server. The NMS server first searches local memory  987   a  for the port PID. If a managed object including the port PID is found, then the NMS server issues a “Create SONET Path” function call to the managed object including the port PID and the parameters sent by the NMS client. If the port PID is not found, then the NMS server uses the port PID as a primary key into the configuration database to retrieve data corresponding to the port. The NMS server then creates the port managed object, stores it in local memory and then issues the “Create SONET Path” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to add a row in SONET Path Table  600 ′ ( FIG. 60   g ) for each SONET path created by the user. The NMS server assigns a unique path LID  600   a  (i.e., primary key) to each SONET path and inserts this within the corresponding row. The NMS server also enters data representing attributes for each SONET path (e.g., time slot, number of time slots, etc.) and the unique port PID  600   b  (i.e., foreign key for association) corresponding to the selected port. 
   As previously discussed, each SONET path corresponds to a port (e.g.,  571   a,    FIGS. 36   a – 36   b ) on a universal port card (e.g.,  554   a ) and is connected through a cross-connection card (e.g.,  562   a ) to a service end point corresponding to a port (i.e., slice) on a forwarding card (e.g.,  546   c ). In one embodiment, after filling in one or more rows in SONET Path Table  600 ′, the NMS server also fills in one or more corresponding rows in Service EndPoint Table (SET) 76″ ( FIG. 60   h ). The NMS server assigns a unique service endpoint LID  76   a  (i.e., primary key) to each service endpoint and inserts the service endpoint LID within a corresponding row. The NMS server also inserts the corresponding path LID  76   b  (i.e., foreign key for association) within each row and may also insert attributes associated with each service endpoint. For example, the NMS server may insert the quadrant number corresponding to the selected port and may also insert other attributes (if provided by the user) such as the forwarding card slice PID ( 76   d ) corresponding to the service end point, the forwarding card PID ( 76   c ) on which the port/slice is located and the forwarding card time slot ( 76   e ). Alternatively, the NMS server only provides the quadrant number attribute and a policy provisioning manager (PPM)  599  ( FIG. 37 ) decides which forwarding card, slice (i.e., payload extractor chip) and time slot (i.e., port) to assign to the new universal port card path, and once decided, the PPM fills in SET Table  76 ″ attribute fields (i.e., self-completing configuration record). 
   For each service endpoint created, the database access commands also cause the configuration database to add a row in an interface table. For example, for each service endpoint corresponding to a SONET path configured for ATM service—that is, service field  942   h  ( FIG. 5   q ) indicates ATM service—a row is added to ATM Interface Table  114 ″ ( FIG. 60   i ). Alternatively, if service field  942   h  is configured for another service, for example, IP, MPLS or Frame Relay, then a row would be added to an interface table corresponding to that upper layer network protocol. The NMS server assigns a unique ATM interface (IF) LID  114   a  (i.e., primary key) and within each row inserts both the assigned ATM IF LID  114   a  and the service endpoint LID  114   b  (i.e., foreign key for association) corresponding to each ATM interface. The NMS server also inserts in each row data representing attributes (e.g., ATM group number) for each ATM interface. The attribute data may be default values and/or data received within the database access commands. 
   Again, when tables in the configuration database are updated an active query feature is used to notify other processes including NMS database  61  ( FIG. 59 ) and any NMS server currently connected to the network device, for example, NMS server  851   a.  Each NMS server builds a configuration object for each changed logical managed object and sends the configuration object to any NMS clients that currently have access to the network device corresponding to the changed logical managed objects, for example, NMS client  850   a.  The NMS clients use the received configured object to update GUI tables  985  and display the configuration changes to a user. Thus, the user that created the SONET path(s) would then be able to see the new paths displayed in SONET path tab  942  ( FIG. 5   q ) and new ATM interfaces displayed in ATM interface tab  946  ( FIG. 5   r ). 
   Similarly, a user may select Virtual ATM Interfaces tab  947  ( FIG. 5   s ) and then select Add button  947   b  to add a virtual ATM interface to an ATM interface selected in navigation tree  947   a.  When the user selects OK button  950   e  ( FIG. 5   t ) in virtual ATM interfaces dialog box  950 , the NMS client places an “Add Virtual ATM Interface” function call to the proxy corresponding to the port associated with the selected ATM interface. The function call includes the ATM interface LID (stored in the GUI table), the corresponding port PID and the parameters provided by the user through the ATM interfaces dialog box. The function call causes the NMS client to send JAVA RMI messages to the NMS server. The NMS server first searches local memory  987   a  for the port PID. If a managed object including the port PID is found, then the NMS server issues an “Add Virtual ATM Interface” function call to the managed object including the ATM interfaces LID and the parameters sent by the NMS client. If the port PID is not found, then the NMS server uses the port PID as a primary key into the configuration database to retrieve data corresponding to the port. The NMS server then creates the port managed object, stores it in local memory and issues the “Add Virtual ATM Interface” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to add a row in Virtual ATM Interfaces Table  993  ( FIG. 60   d ) corresponding to the virtual ATM interface created by the user. The NMS server assigns a unique virtual ATM interface LID  993   a  (i.e., primary key) to the virtual ATM interface and inserts this within the corresponding row. The NMS server also enters data representing attributes (e.g., A 1 –An) for the virtual ATM interface and the unique ATM interface LID  993   b  (i.e., foreign key for association) corresponding to the selected ATM interface in navigation tree  947   a  ( FIG. 5   s ). Again, through the active query feature, the NMS database and NMS server are notified of the changes made to the configuration database. The NMS server builds a configuration object and sends it to the NMS client which updates the GUI tables to display the added virtual ATM interface (e.g.,  947   c,    FIG. 5   u ) to Virtual ATM Interfaces tab  947 . The configuration object may be temporarily stored in local memory  986 . However, once the GUI tables are updated, the NMS client deletes the configured object from local memory  986 . 
   Because there may be many upper layer network protocol interfaces in network device  540 , the port managed object and port proxy may become very large as more and more function calls (e.g., Add Virtual ATM Interface, Add Virtual MPLS Interface, etc.) are added for each type of interface. To limit the size of the port managed object and port proxy, all interface function calls may be added to logical proxies corresponding to logical upper layer protocol nodes. For example, an ATM node table  999  ( FIG. 60   n ) may be included in configuration database  42 , and when ATM service is first configured by a user on network device  540 , the NMS server assigns an ATM node LID  999   a  (e.g., 5000) and inserts the ATM node LID and the managed device PID  999   b  (e.g., 1) in one row  999   c  in the ATM node table. The NMS server may also insert any attributes (A 1 –An). The NMS server then retrieves the data in the row and creates an ATM logical managed object (ATM LMO). Like the physical managed objects, the ATM logical managed object includes the assigned LID (e.g., 5000), attribute data and function calls. The function calls include Get Proxy and interface related function calls like Add Virtual ATM Interface. The NMS server stores the ATM LMO in local memory  987   a  and issues a Get Proxy function call. After creating the ATM proxy (ATM PX), the NMS server sends the ATM proxy to memory  986  local to NMS client  850   a.  The NMS client uses the ATM proxy to update GUI tables  985 , and then uses it to later make function calls to get ATM interface related data from configuration database  42 . 
   Thus, after the user selects OK button  950   e  ( FIG. 5   t ) in virtual ATM interfaces dialog box  950 , the NMS client places an “Add Virtual ATM Interface” function call to the ATM node proxy. The function call includes the ATM interface LID (stored in the GUI table), the corresponding ATM node LID and the parameters provided by the user through the ATM interfaces dialog box. The function call causes the NMS client to send JAVA RMI messages to the NMS server. The NMS server first searches local memory  987   a  for the ATM node LID. If a managed object including the ATM node LID is found, then the NMS server issues an “Add Virtual ATM Interface ATM interface LID and the parameters sent by the NMS client. If the ATM node LID is not found, then the NMS server uses the ATM node LID as a primary key into the configuration database to retrieve data corresponding to the port. The NMS server then creates the ATM node logical managed object, stores it in local memory and issues the “Add Virtual ATM Interface” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to add a row in Virtual ATM Interfaces Table  993  ( FIG. 60   d ) corresponding to the virtual ATM interface created by the user. The NMS server assigns a unique virtual ATM interface LID  993   a  (i.e., primary key) to the virtual ATM interface and inserts this within the corresponding row. The NMS server also enters data representing attributes (e.g., A 1 –An) for the virtual ATM interface and the unique ATM interface LID  993   b  (i.e., foreign key for association) corresponding to the selected ATM interface in navigation tree  947   a  ( FIG. 5   s ). Again, through the active query feature, the NMS database and NMS server are notified of the changes made to the configuration database. The NMS server builds a configuration object and sends it to the NMS client which updates the GUI tables to display the added virtual ATM interface (e.g.,  947   c,    FIG. 5   u ) to Virtual ATM Interfaces tab  947 . The NMS client then deletes the logical managed objects from local memory  986 .” function call to the managed object including the 
   In the discussion below, virtual connections are added using the ATM node proxy. It should be understood, however, that a port proxy including the virtual connection function calls could be used instead. 
   As explained above, to add a virtual connection, the user may select a port (e.g.,  941   a,    FIG. 5   v ) and then select the “Add Virtual Connection” option from pull down menu  943  or the user may select a virtual ATM interface (e.g.,  947   c,    FIG. 5   v ) in Virtual ATM Interfaces tab  947  and then select Virtual Connections button  947   d.  After creating a virtual connection through Virtual Connection Wizard  952  ( FIGS. 5   w – 5   x ), the user selects Finish button  953   w.  This causes the NMS client to place an “Add Virtual Connection” function call to the ATM node proxy. The function call includes the virtual ATM interface LID (stored in the GUI table), the corresponding ATM node PID and the parameters provided by the user through the Virtual Connection Wizard. The function call causes the NMS client to send JAVA RMI messages to the NMS server. The NMS server first searches local memory  987   a  for the ATM node LID. If a managed object including the ATM node LID is found, then the NMS server issues an “Add Virtual Connection” function call to the managed object including the virtual ATM interface LID and the parameters sent by the NMS client. If the ATM node LID is not found, then the NMS server uses the ATM node LID as a primary key into the configuration database to retrieve data corresponding to the ATM node. The NMS server then creates the ATM node logical managed object, stores it in local memory and then issues the “Add Virtual Connection” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to add a row in Virtual Connection Table  994  ( FIG. 60   k ) corresponding to the virtual connection created by the user. The NMS server assigns a unique virtual connection LID  994   a  (i.e., primary key) to the virtual connection and inserts this within the corresponding row. The NMS server also enters data representing attributes (e.g., A 1 –An) for the virtual connection and the unique virtual ATM interface LID  994   b  (i.e., foreign key for association) corresponding to the selected virtual ATM interface in Virtual ATM Interfaces tab  947  ( FIG. 5   v ). 
   In addition to adding a row to Virtual Connection table  994 , when a virtual connection is created one or more rows are also added to Virtual Link Table  995  ( FIG. 601 ) and Cross-Connection Table  996  ( FIG. 60   m ). With regard to Virtual Link Table  995 , the NMS server assigns a unique virtual link LID  995   a  (i.e., primary key) to each endpoint in the virtual connection and inserts each endpoint LID within a row in the Virtual Link Table. The NMS server also enters data in each row representing attributes (e.g., A 1 –An) for the corresponding endpoint and the unique virtual connection LID  995   b  (i.e., foreign key for association) corresponding to the newly created virtual connection  994   a  ( FIG. 60   k ). For a point-to-point connection there will be two end points—that is, two rows are added to the Virtual Link Table each including a unique endpoint LID  995   a  and the same virtual connection LID  995   b  (corresponding to the same virtual connection LID  994   a ,  FIG. 60   k ). For a point to multipoint connection there will be one source endpoint and multiple destination endpoints—that is, more than two rows are added to the Virtual Link Table, one row corresponding to the source endpoint and one row corresponding to each destination endpoint, where each row includes a unique endpoint LID  995   a  and the same virtual connection LID  995   b  (corresponding to the same virtual connection LID  994   a ,  FIG. 60   k ). 
   Each row/record in Cross-Connection Table  60   g,  represents the relationship between the various endpoints and virtual connections. One row is created for each point-to-point connection while multiple rows are created for each point-to-multipoint connection. The NMS server assigns a unique cross-connection LID  996   a  (i.e., primary key) to each cross-connection and inserts each cross-connection LID within a row in the Cross-Connection Table. The NMS server also enters data in each row representing attributes (e.g., A 1 –An) for the corresponding cross-connection. The NMS server then enters two foreign keys for association: Virtual Link  1  LID  996   b  and Virtual Link  2  LID  996   c . Within Virtual Link  1  LID  996   b  the NMS server inserts the source endpoint LID for the virtual connection. Within Virtual Link  2  LID  996   c , the NMS server inserts a destination endpoint LID for the virtual connection. For each of these Virtual Link LIDs in Virtual a Link Table  995 , the NMS server also inserts Cross-Connection LID  995   c  (corresponding to Cross-Connection LID  996   a  in Cross-Connection Table  996 ). Since a point-to-point connection includes only one destination endpoint, only one row in the Cross-Connection table is needed to fully represent the connection. One or more rows are necessary, however, to represent a point-to-multipoint connection. In each of the other rows, Virtual Link  1  LID  996   b  representing the source endpoint remains the same but in each row a different Virtual Link  2  LID  996   c  is added representing the various destination endpoints. 
   Again, through the active query feature, the NMS database and NMS server are notified of the changes made to the Virtual Connection Table, Virtual Link Table and Cross-Connection Table in the configuration database. The NMS server creates configuration objects for each changed row and sends the configuration objects to the NMS client which updates the GUI tables to display the added virtual connection (e.g.,  948   a,    FIG. 5   z ) in the Virtual Connections tab  948 . 
   In addition to adding rows to tables when logical managed objects are configured, rows are also removed from tables when logical managed objects are deleted. For example, if a user selects a SONET path (e.g.,  942   a,    FIG. 5   q ) from SONET Paths Tab  942  and then selects Delete button  942   g,  the NMS client places a “Delete SONET Path” function call to the proxy corresponding to the selected port. The function call includes the selected port PID as well as the SONET Path LID corresponding to the SONET path to be deleted. The function call causes the NMS client to send JAVA RMI messages to the NMS server. The NMS server first searches local memory  987   a  for the port PID. If a managed object including the port PID is found, then the NMS server issues a “Delete SONET Path” function call to the managed object including the SONET path LID. If the port PID is not found, then the NMS server uses the port PID as a primary key into the configuration database to retrieve data from the row/record corresponding to the port. The NMS server then creates the port managed object, stores it in local memory and issues the “Delete SONET Path” function call. The function call causes the NMS server to generate database access commands and send them to the configuration database within the selected network device. 
   The database access commands cause the configuration database to directly delete the specific row within SONET Path Table  600 ′ ( FIG. 60   g ) corresponding to the SONET path LID (primary key). Through the active query feature, the NMS database and NMS server are notified of the changes made to the SONET Path Table in the configuration database. The NMS server sends JAVA RMI messages to the NMS client to cause the client to update the GUI tables to remove the deleted SONET Path from the SONET Paths tab  942 . 
   Many different function calls may be generated by the NMS client and NMS server to carry out configuration changes requested by users. 
   As described above, memory local to each NMS client is utilized to store proxies corresponding to managed objects associated with physical components within a network device selected by a user. Proxies for logical managed objects corresponding to upper layer network protocol nodes (e.g., ATM node, IP node, MPLS node, Frame Relay node, etc.) may also be stored in memory local to each NMS client to limit the size of physical port proxies. The proxies reduce the load on the network/NMS server by allowing the NMS client to respond to user requests for physical network device data and views without having to access the NMS server. Storing data local to the NMS client improves the scalability of the NMS server by not requiring the NMS server to maintain the managed objects in memory local to the server. Thus, as multiple NMS clients request access to different network devices, the NMS server may, if necessary, overwrite managed objects within its local memory without disrupting the NMS client&#39;s ability to display physical network device information to the user and issue function calls to the NMS server. Response time to a user&#39;s request for access to a network device is also improved by initially only retrieving physical data as opposed to retrieving both physical and logical data. 
   In addition, unique identification numbers—both PIDs and LIDs—may also be stored in memory local to the NMS client (e.g., within proxies or GUI tables) to provide improved data request response times. Instead of navigating through the hierarchy of tables within the relational configuration database internal to the network device, the NMS server is able to use the unique identification numbers as primary keys to directly retrieve the specific data needed. Providing the unique identification numbers from the NMS client to the NMS server insures that even if the NMS server needed to overwrite managed objects within memory local to the NMS server, the NMS server will be able to quickly re-generate the managed objects and quickly retrieve the necessary data. 
   The unique identification numbers—both PIDs and LIDs—may be used in a variety of ways. For example, as previously mentioned, the device mimic  896   a  ( FIG. 4   t ) is linked with status window  897 , such that selecting a module in device mimic  896   a  causes the Module tab to highlight a line in the inventory corresponding to that card. The unique PIDs and LIDs are utilized to make this link between the status window and the device mimic. 
   Network Device Authentication: 
   When a user selects an IP address (i.e., 192.168.9.202,  FIG. 4   e ) representing a particular network device from device list  898   b  in GUI  895 , a network management system (NMS) client (e.g.,  850   a,    FIG. 2   b ) sends a message to an NMS server (e.g.,  851   a ) and the NMS server uses the IP address to connect to the network device (e.g.,  540 ) to which that IP address is assigned. The NMS server may connect to a network device port on a universal port card for in-band management or a port on an external Ethernet bus  41  ( FIGS. 13   b  and  35   a – 35   b ) for out-of-band management. 
   For out-of-band management, the NMS server uses the IP address over a separate management network, typically a local area network (LAN), to reach an interface  1036  ( FIGS. 63   a – 63   b ) on the network device to external Ethernet bus  41 . Any intermediate network may exist between the local network to which the NMS is connected and the local network (i.e., Ethernet  41 ) to which the network device is connected. A Media Access Control (MAC) address (hereinafter referred to as the network device&#39;s external MAC address) is then used on Ethernet  41  to bridge the packet, containing the IP address, to the network device. 
   The Institute of Electrical and Electronics Engineers (IEEE) is responsible for creating and assigning MAC addresses, and since one independent party has this responsibility, MAC addresses are assured to be globally unique. Network hardware manufacturers apply to the IEEE for a block (e.g., sixteen thousand, sixteen million) of MAC addresses. MAC addresses are normally 48 bits (6 bytes) and the first three bytes represent an Organization Unique Identifier (OUI) assigned by the IEEE. During manufacturing, the network hardware manufacturer assigns a MAC address to each piece of hardware having an external LAN connection. For example, a MAC address is assigned to each network device card on which an external Ethernet port is located when the card is manufactured. Typically, MAC addresses are stored in non-volatile memory within the hardware, for example, a programmable read only memory chip (PROM), which cannot be changed. Thus, MAC addresses provide a unique physical identifier for the assigned hardware and may be used as unique global identifiers for individual network device cards including external Ethernet ports. 
   Referring to  FIGS. 63   a – 63   b , in one embodiment, an external Ethernet network interface  1036  for connecting network device  540  to external Ethernet  41  is located on management interface (MI) card  621  (see also  FIG. 41   a ), and the IEEE provided MAC address (i.e., external MAC address) assigned to the MI card is stored in PROM  1038 . 
   Preferably the network device includes an internal Ethernet bus  544  (or  32  in  FIG. 1 ) to which each card including a processor is connected. In this embodiment, MI card  621  does not connect directly to internal Ethernet bus  544  but instead connects to external control card  542   b  and redundant external control card  543   b.  Each card that connects to internal Ethernet bus  544 —for example, external control cards  542   b  and  543   b,  internal control cards  542   a  and  543   a,  switch fabric cards  570   a  and  570   b,  forwarding cards  546   a – 546   e,    548   a – 548   e,    550   a – 550   e,  and  552   a – 552   e,  universal port cards  554   a – 554   h,    556   a – 556   h,    558   a – 558   h  and  560   a – 560   h,  and cross connection cards  562   a – 562   b,    564   a – 564   b,    566   a – 566   b  and  568   a – 568   b —includes an internal Ethernet network interface and may communicate with each of the other cards connected to the internal Ethernet using an internal address. In one embodiment, the internal address for each card is an assigned IEEE provided MAC address, which is stored in non-volatile memory (e.g., a PROM) on the card. Since IEEE assigned MAC addresses are limited and since traffic on internal Ethernet  544  is not sent directly over external Ethernet  41 , instead of using IEEE assigned MAC addresses as internal addresses, another unique identifier may be used. For example, the unique serial number of each card may be stored within and readable from a register on each card and may be used as the internal address. The serial number may also be combined with other identifiers specific to the card, for example, the card&#39;s part number. The serial number or the combination of serial number and part number for each card may then be used as a unique internal address and physical identifier for the card. 
   As previously discussed, the IP addresses listed in device list  898   b  ( FIG. 4   e ) come from a user profile previously created for the user. Since the IP address assigned to each network device may change after the user profile is created, the NMS needs a mechanism in addition to the IP address that will ensure that the device to which it is connected is the same network device associated with the set of network device attributes (i.e., capabilities and current configuration) corresponding to the IP address in the user profile. Each time a user selects a network device in device list  898   b  and/or periodically, for example, every six hours, the NMS will then use the mechanism to authenticate the identity of the network device. 
   In one embodiment, the authentication mechanism uses two or more of the network device&#39;s physical identifiers. For example, the external MAC address (i.e., IEEE assigned) may be used for authentication with one or more of the internal addresses (i.e., IEEE assigned MAC addresses or other unique identifiers such as serial numbers). As another example, two or more internal addresses may be used for authentication. As a result, a combination of a user entered identifier—the IP address assigned to the network device—and two or more physical identifiers—the external MAC address and/or one or more internal addresses—are used to guarantee the identity of each network device in the network. 
   As described above, when a network device is added to a network, an administrator selects an Add Device option in a pop-up menu  898   c  ( FIG. 6   a ) in GUI  895  to cause a dialog box (e.g.,  898   d,    FIG. 6   b;    1013 ,  FIG. 11   u ) to be displayed. After entering the required information into the dialog box, the user selects an Add button (e.g.,  898   f,    FIG. 6   b;    1013   h,    FIG. 11   u ). Selection of the Add button causes the NMS client to send the data from the dialog box to the NMS server. The NMS server adds a row to Administration Managed Device table  1014 ′ ( FIG. 64 ) and inputs the data sent from the NMS client into the new row. In addition, the NMS server uses the IP address in the data sent from the NMS client to connect with the network device and retrieve two or more physical identifiers. The physical identifiers may then be stored in columns (e.g.,  1014   e ′ and  1014   f ′) of the Administration Managed Device table. Although only two physical identifier (ID) columns are shown in  FIG. 64 , the Administration Managed Device table may include additional columns for additional physical identifiers. 
   Since MAC addresses are 48 bits in length, they may be too large to store as integers within the NMS database when the NMS database is a relational database. When one or more MAC addresses are used as physical identifiers, therefore, the NMS server converts the 48 bit MAC addresses into strings before storing them in columns  1014   e ′ and  1014   f ′ in the new row of the Administration Managed Device table. 
   The NMS server may be programmed to retrieve the physical identifier associated with any card within the network device for input into the Administration Managed Device table. Preferably, the retrieved physical identifiers correspond to cards least likely to fail and least likely to be removed from the network device. Cards with the smallest number of components or less complex hardware may be least likely to fail and may be least likely to be removed from the network device and replaced with an upgraded card. 
   With respect to the current embodiment, MI card  621  includes the smallest number of components and may be the card least likely to fail or be removed from network device  540 . Thus, the external MAC address for MI card  621  may be retrieved by the NMS server and input into one of the physical identifier columns in the Administration Managed Device table. Since the network device requires at least one internal control card  542   a  or  543   a  to be present in order to operate, the internal address associated with one of the internal control cards may be retrieved and input into one of the physical identifier columns in the Administration Managed Device table along with the physical identifier for MI card  621 . Since internal control card  542   b  is a backup card for internal control card  542   a  and at least one is required to be operational, it is highly unlikely that both cards will fail or be removed from the network device simultaneously. Therefore, instead of or in addition to retrieving the external MAC address associated with MI card  621 , the internal addresses for both internal control cards may be retrieved by the NMS server and input into the physical identifier columns in the Administration Managed Device table. Similarly, the internal addresses for the external control cards or the switch fabric cards may be retrieved and input into the physical identifier columns in the Administration Managed Device table. The internal addresses corresponding to the forwarding cards, universal port cards and cross connection cards may also be retrieved and input into the Administration Managed Device table, however, since these cards support customer demands which are likely to change, it is highly likely that these cards will be removed or replaced within the network device and, therefore, these internal addresses are not preferred as the physical identifiers for authentication. 
   Authentication may be accomplished using two or more physical identifiers retrieved from a network device regardless of whether the network device includes an internal Ethernet. As described above, each network device card may include a serial number stored in a register on the card. Alternatively, another type of unique identifier may be stored in non-volatile memory. In either case, since the unique identifier is tied to the card, it is a physical identifier, and authentication may be accomplished by retrieving the physical identifier—through the in-band network—from two or more cards within the network device. 
   As described above, the Administration Managed Device table provides a centralized set of device records shared by all NMS servers. The LID in column  1014   a ′, therefore, provides a single “global” identifier for each network device that is unique across the network and accessible by each NMS server, and each record in the Administration Managed Device table provides a footprint that uniquely identifies each device. The global identifier (i.e., the LID from column  1014   a ′) may be used for a variety of other network level activities. For example, the global identifier may be sent by the NMS server to the network device and included in accounting/statistical data (or in the file names containing the data) by Usage Data Server (UDS)  412   a  or FTP client  412   b  ( FIG. 13   c ) sent from the network device to external file system  425 . Since all data gathered within the network is associated with a unique global identifier, data collector server  857  may then run reports across all devices in the network. For example, a report may be run to determine which network device is least utilized and another report may be run to determine which network device is most utilized. The network administrator may then use these reports to transfer services from the most utilized to the least utilized to better balance the load of the network. 
   As described above, after the data from dialog box  1040  ( FIG. 64 ) is added to the Administration Managed Device table, the data corresponding to the network device is added to user profile logical managed objects (LMOs) when users authorized to access the network device log into an NMS client. Once added to a user profile LMO, the IP address associated with that network device is added to device list  898   b  ( FIG. 4   e ). In one embodiment, each time a user selects a network device IP address in device list  898   b,  the NMS server connects to the network device and authenticates the network device by retrieving the physical identifiers from the appropriate cards in the network device. In addition or alternatively, an NMS server may periodically connect to each network device in the telecommunications network and authenticate each network device by retrieving the physical identifiers from the appropriate cards in the network device. 
   In one embodiment, the network device is authenticated by comparing the physical identifiers retrieved from the network device to the physical identifiers stored either in the Administration Managed Device table or each user profile. If both physical identifiers match, then the network device is authenticated. In addition, if only one physical identifier matches, the network device is also authenticated. One physical identifier may not match because the associated card may have been removed from the network device and replaced with a different card having a different physical identifier. In this event, the NMS server still automatically authenticates the network device without user intervention and may also change the physical identifier in the Administration Managed Device table and perhaps the user profile immediately or schedule an update during a time in which network activity is generally low. 
   Since electronic hardware may fail, it is important that all network device electronic hardware be removable and replaceable. However, if all electronic hardware is removable, no permanent electrical hardware storing a physical identifier may be used to definitively identify the network device. Using multiple physical identifiers to uniquely identify network devices provides fault tolerance and supports the modularity of electronic hardware (e.g., cards) within a network device. That is, using multiple physical identifiers for authentication allows for the fact that cards associated with physical identifiers used for authentication may be removed from the network device. Through the use of multiple physical identifiers, even if a card associated with a physical identifier used for authentication is removed from the network device, the network device may be authenticated using the physical identifier of another card. If more than two physical identifiers are used for authentication, a network device may still be authenticated even if more than one card within the device is removed as long as at least one card corresponding to a physical identifier being used for authentication is within the device during authentication. 
   Importantly, the present invention allows for dynamic authentication, that is, the NMS is able to update its records, including physical identifiers, over time as cards within network devices are removed and replaced. As long as one card associated with a physical identifier within the user profile LMO is in the network device when authentication is performed, the network device will be authenticated and the NMS may then update its records to reflect any changes to physical identifiers associated with other cards. That is, for cards that are removed and replaced, the NMS will update the Administration Managed Device table with the new physical identifiers corresponding to those cards and if a card was removed and not replaced, the NMS will remove the physical identifier corresponding to that card from the Administration Managed Device table. For example, in the embodiment described above, if the card associated with the physical identifier stored in physical ID A is removed and replaced and the card associated with the physical identifier stored in physical ID B is in the network device during authentication, the network device will be authenticated and the NMS may insert the new physical identifier corresponding to the new card in physical ID A. Then if the card associated with the physical identifier stored in physical ID B is removed and replaced, the network device will still be authenticated during the next authentication so long as the card associated with the new physical identifier stored in physical ID A is in the network device. 
   Instead of storing multiple physical identifiers in the Administration Managed Device table, a single string representing a composite of two or more physical identifiers may be stored in one column of the Administration Managed Device table. For example, the physical identifiers corresponding to two or more cards within the network device may be multiplied together as integers and the result of the multiplication converted into and stored as one string value in one column of the Administration Managed Device table. With regard to the current embodiment, physical ID A and physical ID B may be multiplied together and stored as a single string. For authentication, the composite string may be converted back into a long integer, be divided by a first retrieved physical identifier corresponding to physical ID A and the result compared with the second retrieved physical identifier corresponding to physical ID B. If the result matches, then the device is authenticated. Otherwise, the converted composite value is divided by the second retrieved physical identifier corresponding to physical ID B and the result is compared with the first retrieved physical identifier corresponding to physical ID A. If the result matches, then the device is authenticated. Storing a multiplied product of physical identifiers works similarly for more than two physical identifiers, and other composite values and corresponding comparisons may also be used to provide authentication of multiple physical identifiers. In addition, since the composite value will be a single, unique value derived from two or more physical identifiers, it may be inserted in LID column  1014   a ′ of the Administration Managed Device table instead of a separate column. 
   If all cards associated with physical identifiers being used for authentication are removed and/or replaced within a network device, then the NMS server will be unable to authenticate the network device and the NMS server will notify the NMS client which will notify the user. The user may confirm through a dialog box that the network device to which the NMS server was connected using the IP address in the user profile is indeed the correct network device in which case the NMS server would update the physical identifiers in the Administration Managed Device table and/or the user profile immediately or at a predetermined future time. If the user indicates that the network device is not the same, then the NMS server removes the IP address from the record in the Administration Managed Device table and/or requests the user to provide a new IP address for that network device. As a result, a network administrator may re-configure a network and assign new IP addresses to a variety of network devices and the set of attributes associated with each network device will not be lost. Instead the user may be prompted to input the new IP address for each network device corresponding to a changed IP address. As a result, the present invention also allows for dynamic authentication over time as the IP addresses assigned to network devices are changed. 
   The above discussion uses MAC addresses, serial numbers and a combination of serial numbers and part numbers as examples of physical identifiers that may be used to authenticate a network device. It is to be understood that a network device may be authenticated through multiple other physical identifiers. For example, memory on each network card may include a different unique identifier, perhaps provided by a user. In addition to storing the IP address and physical identifiers in the Administration Managed Device record, additional identifiers may also be included in each record. For example, a user may be prompted to supply a unique identifier for each network device. 
   Internal Dynamic Health Monitoring: 
   To improve network device availability, many current network devices include internal monitoring and evaluation of particular network resource attributes. The evaluations, however, are based upon simple threshold values and fixed expressions. In addition, the resource attributes that may be monitored are limited to particular predetermined resource attributes. The present invention allows network managers to dynamically select a threshold evaluation expression from a list of available expressions or input a new threshold evaluation expression. In addition, any attribute associated with an identifiable resource within the network device may be evaluated against the chosen or input expression. 
   Referring to  FIG. 65 , processes within network device  540  may include attributes (i.e., parameters) corresponding to network device resources that a network manager may wish to check against particular threshold expressions (i.e., rules). For each of these processes, a Threshold Monitoring Library (TML)  1046  is linked in when they are built. For example, within network device  540 , SONET drivers (e.g.,  415   a ) and ATM drivers (e.g.,  417   a ) link in TML  1046  when built to allow resource attributes corresponding to those applications to be checked against threshold rules. When an application including the TML is first loaded within network device  540 , the TML linked into each application causes the applications to retrieve the threshold rules and other threshold data from tables within configuration database  42 . In one embodiment, these tables include a Dynamic Threshold table  1048 , a Threshold Rule table  1050  and a Threshold Group table  1052 , described in detail below. The application/TML also establishes active queries (discussed above) for table entries relevant to each application such that if entries are added to or removed from these tables, the configuration database automatically notifies the appropriate application/TML of the change. 
   The TML maintains a sampling timer for each resource attribute corresponding to its associated application and selected by the user for threshold evaluation. The sampling frequency for each resource attribute is retrieved from the Dynamic Threshold table, and at the appropriate sampling frequency, the TML retrieves each resource attribute value from the corresponding application and checks the resource attribute value against a threshold rule and other variables retrieved from the Dynamic Threshold table. If the threshold rule is met, then, in accordance with a reporting structure also retrieved from the Dynamic Threshold table, the application/TML may do nothing or notify an SNMP master agent  1042  and/or a global log service  1044 . The SNMP master agent causes SNMP traps to be sent to appropriate NMS servers (e.g.,  851   a ), while the Global Log Service logs the event in one or more files within hard drive  421 . 
   In one embodiment, to establish a threshold evaluation for a resource attribute, a user (e.g., a network manager) selects a resource in graphical user interface (GUI)  895  ( FIGS. 66   a – 66   e ) and then selects a Threshold menu option  1054  to cause a Threshold dialog box  1056  ( FIG. 67 ) to be displayed. For example, a user may select SONET Path  942   a  ( FIG. 66   a ), ATM Interface  946 b ( FIG. 66   b ), Virtual ATM Interface 947 c  ( FIG. 66   c ) or Virtual Connection  948   a  ( FIG. 66   d ) and then Threshold menu option  1054  to cause a Threshold dialog box  1056  ( FIG. 67 ) to be displayed. As another example, for attributes related to network device hardware resources—for example, unused hard drive space—the user may select a card (e.g., internal processor control card  542   a,    FIG. 66   e ) corresponding to the hardware resource (e.g., hard drive  421 ,  FIG. 65 ) and attribute (e.g., hard drive space) and then select Threshold menu option  1054  to cause the Threshold dialog box to be displayed. 
   The Threshold dialog box may include many different elements. In one embodiment, the Threshold dialog box includes a Resource element  1056   a,  an Attribute element  1056   b,  a Threshold Rule element  1056   c,  a Sampling Frequency element  1056   d  and an Action element  1056   e.  The resource element window  1056   j  is automatically filled in with a resource name corresponding to the resource selected by the user. If the user&#39;s selection (e.g., a hardware component) is associated with more than one resource, a default resource name is entered in window  1056   j  and the user may accept that resource name or choose a different resource name from pull down menu  1056   f.  Default values may also be inserted in attribute window  1056   k,  the threshold rule window  1056 L and the sampling frequency window  1056   m.  Again, the user may accept these default values or select a value from corresponding pull-down menus  1056   h – 1056   i.    
   The Attribute element identifies the specific resource attribute that is to be examined against the threshold rule. For example, the resource may be a SONET path and the attribute may be “unavailable seconds” indicating that the user wants to check the number of seconds the selected SONET path is unavailable against the threshold rule. The corresponding applications—in this case, SONET drivers—maintain values (for example, in counters) associated with the attribute or have access to other applications that maintain values associated with the attribute. For example, a SONET driver may maintain a counter for seconds that a SONET path is unavailable or the attribute may correspond to a Management Information Base (MIB) Object Identifier (OID) and the SONET driver may access an SNMP subagent to retrieve the current value for the MIB OID. The MIB OID identifies a table and statistic maintained by the SNMP subagent. 
   As described above, user profiles may be used to limit each user&#39;s access to particular network device resources. In addition, a user profile may be used to limit which network device resource attributes a user may evaluate against thresholds. For example, a user profile may list only those attributes the user associated with the profile may evaluate, and this list of attributes may be made available to the user through the Threshold dialog box attribute element pull-down menu  1056   g.    
   With respect to the Threshold Rule element and Sampling Frequency element, in addition to choosing the default value or a value from the corresponding pull-down menu, the user may type a different value into windows  1056 L and  1056   m.  For example, pull-down menu  1056   h  may list ten possible rules or expressions, one of which is chosen as the default value and automatically listed in window  1056 L. The user may accept the default value, select one of the other nine rules listed in the pull-down menu or type in a new expression in window  1056 L. 
   The Threshold Rule element identifies the expression against which the attribute for the selected resource will be checked. For example, the threshold rule may be a simple expression such as “if attribute&gt;10”, “if attribute is&lt;5”, “if attribute is&gt;10 or &lt;5” or “if attribute=0”. As another example, the threshold rule may be a more complex expression such as an expression using the Remote Monitoring (RMON) MIB as a model. Since network devices generally have peak time periods when a large amount of network traffic is transmitted and received and off-peak time periods when less network traffic is transmitted and received, a user may want a threshold rule to include the time of day. For example, the user may want to be notified if an attribute (e.g., failed call attempts) for a resource (e.g., ATM interface) is greater than 10 during the hours between 8:00 am and 7:00 pm or greater than 5 between the hours of 7:00 pm and 8:00 am. To accomplish this, the user might select or input the following expression: “if failed call attempts&gt;10 between 8:00 am–7:00 pm or &gt;5 between 7:00 pm–8:00 am”. As another example, the user may want to be notified when a particular attribute exceeds a threshold and then only if it remains over that threshold for a particular number of sampling periods (hereinafter referred to as frequency of events (FOE) threshold rule). Again, the user may simply select or enter an expression for the FOE threshold rule. The NMS client may add any new rules to pull-down menu  1056   h.    
   The Sampling Frequency element identifies the periodicity with which the attribute for the selected resource will be checked against the threshold rule. As described below, the user may select a sampling frequency (e.g., seconds, minutes, hours, days, weeks, etc.) from a pull-down menu or type in a new sampling frequency (e.g., 6 hours). In general, users set sampling frequencies based upon the criticality of the failure. That is, sampling frequencies will be shorter for those attributes that are used to detect critical network device failures. A short sampling frequency (e.g., five minutes) on a critical resource attribute may allow the network manager to be quickly notified of any issues such that the network manager may address the issue and prevent the failure. 
   To receive notices of a threshold event for the selected resource, the user selects NMS element  1056   n  within Action element  1056   e  of the Threshold dialog box. Selecting NMS element  1056   n  causes TMLs within applications including that resource attribute to report threshold events to SNMP master agent  1042  ( FIG. 65 ) or another central process used to manage the distribution of events/traps. The SNMP master agent then sends an SNMP trap to the appropriate NMS server, which notifies the appropriate NMS client, which displays a notice to the user through GUI  895 . Alternatively or in addition, the user may select Log element  1056   o  within Action element  1056   e  of the Threshold dialog box to cause threshold events to be logged. Selecting Log element  1056   o  causes TMLs within applications including the selected resource attribute to report threshold events to Global Log Service  1044  ( FIG. 65 ). The Global Log Service then stores the event in one or more log files within hard drive  421 . 
   When the user is finished selecting and entering values for the elements within the Threshold dialog box, the user selects an OK button  1056   p.  The NMS client sends the data from the Threshold dialog box to an NMS server (e.g., NMS server  851   a,    FIG. 65 ). As described above, although hidden from the user, the NMS client saves the logical identification (LID) or physical identification (PID) associated with each resource within the GUI tables, and the data sent by the NMS client to the NMS server includes the LID/PID associated with the selected resource. For example, SONET path  942   a  ( FIG. 66   a ) may have been assigned LID  901  ( FIG. 60   g ), and any threshold data sent from an NMS client to an NMS server and corresponding to SONET path  942   a  will include LID  901 . The NMS server uses the received data to update tables in configuration database  42  of the network device selected in GUI  895 . 
   Referring to  FIG. 68 , specifically, within Dynamic Threshold table  1048 , the NMS server enters the resource ID (LID or PID) into column  1048   a,  the attribute into column  1048   c,  the sampling frequency into column  1048   d,  the reporting structure (log and/or SNMP trap) into action column  1048   e  and the threshold evaluation expression into rule column  1048   f.  The evaluation expression is stored as a string value in rule column  1048   f.  To avoid having duplicate records for the same resource ID and threshold name, the NMS server first searches Dynamic Threshold table  1048  for records (i.e., rows) including the same resource ID and attribute. If a match is found, then the NMS server updates the values in the other columns with the new data received from the NMS client. If a match is not found, then the NMS server creates a new row and inserts all the data received from the NMS client. 
   The network manager is likely to want to evaluate many similar resources in a similar way. For example, a network manager may want to evaluate a large number of SONET paths against the same attributes and rules using the same sampling frequency and reporting structure. That is, for each of these many SONET paths, the network manager may want to evaluate the same attribute (e.g., path errors (path end), path errors (far end), unavailable seconds (path end), unavailable seconds (far end), etc.) using the same evaluation expression (e.g., attribute &gt;10), sampling frequency (e.g., 15 minutes) and reporting structure (e.g., SNMP trap). Having a row for each resource ID in the Dynamic Threshold table, therefore, leads to a large amount of repetitive data. 
   To reduce the amount of repetitive data, one or more rows in the Dynamic Threshold table may represent a threshold group that may be associated with multiple resource IDs. 
   Referring to  FIG. 69   a,  Dynamic Threshold table  1048 ′ includes a threshold group LID column  1048   a ′ and a resource column  1048   b ′ instead of the resource ID column (e.g.,  1048   a,    FIG. 68 ) found in Dynamic Threshold table  1048 . Threshold group LID column  1048   a ′ corresponds to threshold group LID column  1052   b  in Threshold Group table  1052  ( FIG. 69   b ). Threshold Group table  1052  further includes a resource ID column  1052   a.    
   The TML in each application uses the Threshold Group table to associate each resource ID with a threshold group LID. As a result, one or more resource IDs may be associated with the same threshold group LID. For example, within Threshold Group table  1052 , SONET path LIDs  901  and  903  are associated with threshold group LID  8312 . Within Dynamic Threshold table  1048 ′, threshold group LID  8312  corresponds to three rows each of which corresponds to a different attribute (e.g., section errors, line errors (line end) and line errors (far end)). As a result, instead of having three rows for each SONET path LID  901  and  903 , the Dynamic Threshold table  1048 ′ includes only three rows shared by both SONET path LIDs. The TMLs within the SONET drivers corresponding to SONET path LIDs  901  and  903 , therefore, each use the attributes, sampling frequencies, reporting structures and rules in the three rows corresponding to threshold group LID  8312 . Although not shown, additional SONET path LIDs may also be associated with threshold group  8312 , and other SONET path LIDs (e.g.,  902 ) may be associated with other threshold groups (e.g.,  8313 ). 
   As previously mentioned, SONET paths are only one type of resource and many other types of resources with various constraints may be checked against threshold rules. For example, an ATM interface assigned an LID of  5054  may be associated with threshold group  8433  in Threshold group table  1052 , and threshold group  8433  may include multiple records in Dynamic Threshold table  1048 ′ each of which corresponds to a different attribute, for example, failed call attempts and has errors. As another example, a virtual connection assigned an LID of  7312  may be associated with threshold group  8542 , and threshold group  8542  may also include multiple records in Dynamic Threshold table  1048 ′ each of which corresponds to a different attribute, for example, received (Rx) traffic and transmitted (Tx) traffic. Any resource including an assigned LID or PID and at least one measurable attribute may be checked against a threshold expression. 
   Where Dynamic Threshold table  1048 ′ is implemented, once the NMS server receives threshold data from the NMS client, the NMS server searches the Threshold Group table for the resource LID/PID. If a match is found, then the NMS server searches the Dynamic Threshold table for records associated with the threshold group LID corresponding to the resource LID/PID. The NMS server then compares the attribute in the data received from the NMS client to the attributes retrieved from each record in the Dynamic Threshold table. If a match is found, the NMS server compares the remaining data received from the NMS client to the data retrieved from that record in the Dynamic Threshold table. If any of the data does not match, then the NMS server first searches Threshold Group table  1052  for the threshold group LID to determine if any other resources correspond to that group LID. If no, then the NMS server does not need to create a new threshold group and simply updates the group records in the Dynamic Threshold table. If yes, then the NMS server needs to create a new threshold group and does so by adding a new row in the Dynamic Threshold table, inserting the data received from the NMS client, and assigning a new threshold group LID. The NMS server then updates the record in the Threshold Group table associated with the resource LID/PID with the new threshold group LID. The NMS server also copies over any additional records associated with the original threshold group LID but for different attributes into new records in the Dynamic Threshold table and inserts the new threshold group LID. 
   Many threshold groups may use the same basic rule/evaluation expression with the same or different variables. For example, a common threshold evaluation expression may be “if attribute&gt;a”, where ‘a’ is a variable. A network manager may want to be notified if the section errors on a SONET path exceed 10 and if the has errors on an ATM interface exceed 13. Within Dynamic Threshold table  1048  ( FIG. 68 ), rule column  1048   f  for both records  1048   g  and  1048   h  would include different strings because although the basic expression is the same, the threshold variable (e.g., 10, 13) is different for both records. To allow rules to be shared by many threshold groups, Dynamic Threshold table  1048 ″ ( FIG. 70   a ) includes a rule LID column  1048   f ″ and threshold variable columns  1048   g ″– 1048   t ″. More or less variable columns may be included in the Dynamic Threshold table. 
   The identification numbers stored in rule LID column  1048   f ′ correspond to identification numbers stored in rule LID column  1050   a  ( FIG. 70   b ) in Threshold Rule table  1050 . The Threshold Rule table also includes an expression column  1050   b  within which are stored the basic rules that may be shared by one or more threshold groups in Dynamic Threshold table  1048 ″. For example, row  1050   c  in the Threshold Rule table includes a rule LID of  9421  and an expression of “if attribute&gt;a”. This rule LID of  9421  may be included in both rows  1048   u ″ and  1048   v ″ of Dynamic Threshold table  1048 ″ to allow both threshold groups  8312  and  8433  to share that expression string. In addition, each variable needed by the expression is stored in one of the variable columns  1048   g ″– 1048   t ″. Thus, for threshold group LID  8312  in record  1048   u ″, the expression is converted into “if section errors&gt;10”, and for threshold group LID  8433 , the expression is converted into “if hcs errors&gt;13”. 
   When the user adds a new expression to Threshold dialog box  1056  ( FIG. 67 ), the NMS server adds a row to Threshold Rule table  1050 , strips the new expression of values to provide a basic new expression and inserts the basic new expression in column  1050   b  of the new row. The NMS server also assigns a new rule LID and inserts that into column  1050   a  of the new row. Within Dynamic Threshold table  1048 ″, the NMS server then adds the new rule LID to column  1048   f ″ in the record associated with the threshold group LID corresponding to the resource listed in the Threshold dialog box. The NMS server also adds any variable values to columns  1048   g ″– 1048   t ″ of this same record. 
   Instead of having the TML maintain a sampling timer for a particular resource attribute, the application may continuously track an attribute and then notify the TML if an event occurs. For example, an application, such as Global Log Service  1044  ( FIG. 65 ), may monitor the amount of unused space in hard drive  421  and if that amount falls below a certain level, the Global Log Service application may notify its linked-in TML  1046 . Then, in accordance with the action listed in the Dynamic Threshold table, the TML will send a notice to SNMP master agent  1042  to cause the SNMP master agent to issue an SNMP trap to an NMS server and/or the TML will cause the Global Log Service to log the event. 
   As explained above, many different threshold expressions may be used to evaluate resource attributes. In addition, one or more expressions may be cascaded together—that is, a detected threshold event corresponding to a first threshold expression may cause the TML to begin using a second threshold expression. Referring to  FIG. 71 , Dynamic Threshold table  1048 ′″ may include an Active/Inactive column  1048   w ′″ and each threshold group LID may include two or more rows corresponding to the same resource and attribute. For example, rows  1048   x ′″ and  1048   y ′″ correspond to threshold group LID  8588 , the hard drive resource and the unused disk space attribute. Each row, however, includes a different rule LID  9428 ,  9424  in Rule LID column  1048   f ′″ and, in accordance with Active/Inactive column  1048   w ′″, row  1048   x ′″ starts out as an active threshold evaluation and row  1048   y ′″ starts out as an inactive threshold evaluation. As defined in Threshold Rule table  1050 , rule LID  9428  corresponds to the expression “if attribute is&lt; a,  go to rule LID b”. Within row  1048   x ′″, this converts to “if unused disk space is&lt;80%, go to rule LID  9424 ”. Thus, if the TML detects that less than 80% of unused disk space is available in hard drive  421 , the TML will, in accordance with Action column  1048   e ′″, cause the Global Log Service to log the threshold event and then change the status of row  1048   x ′″ to inactive and the status of row  1048   y ′″ to active. Rule  9424  in the Threshold Rule table corresponds to expression “if attribute&lt;a” and with respect to row  1048   y ′″, this converts to “if unused disk space is&lt;20%”. Thus, once the TML detects that the unused disk space is less than 80% (row  1048   x ′″), the TML begins using an increased sampling frequency of every 30 seconds in accordance with row  1048   y ′″ and if the unused disk space is determined to be less than 20% (row  1048   y ′″), then the TML, in accordance with Action column  1048   e ′″ sends a notice to SNMP master agent  1042  to cause the SNMP master agent to send an SNMP trap to the NMS server. Thus, rules  9428  and  9424  are cascaded together. 
   Action column  1048   e ′″ in the Dynamic Threshold table may include any possible action that a process within network device  540  may take. For example, in addition to notifying the Global Log Service and the Master SNMP agent, the process may notify a process capable of sending an e-mail message or a page to the user. Thus, if a network resource attribute causes a threshold event and that resource attribute corresponds to a potentially critical failure, the network manager may want to be paged in order to address the issue as quickly as possible to attempt to avoid the actual failure. 
   Linking the TML into each application having resource attributes that may be checked against thresholds, removes the need to hard code thresholding into these applications. Upgrading or modifying thresholding is, therefore, simplified since only the TML needs to be changed and then re-linked into each application to effect the upgrade/modification. Importantly, the thresholding metadata received from the user, stored in the one or more tables within the configuration database and retrieved by the TML provides massive flexibility to the TML such that TML modifications and upgrades should be very infrequent. For example, in the past, to add new threshold rules, network device software needed to be upgraded and re-released and the network device had to be re-booted. In the present invention, users may directly enter new rules, which are then automatically used within the network device without the need to change or re-release software or reboot the network device. Thus, neither the applications nor the TML need to be changed or re-released to allow the applications and TML to use a new rule. In addition, Threshold dialog box and configuration tables allow the user to continuously change the threshold rules and variables, the resources and attributes that are evaluated, the sampling frequency and the reporting structure. Thus, the user may proactively manage their network by gathering data over time and then change thresholding as needed. In essence, users may customize their network device health monitoring dynamically at their local site, for example, at a network carrier&#39;s premises. 
   The TML and the tables in the configuration database are not application specific or resource type specific. As a result, when new applications are created, they are simply linked with the TML when the application is built and prior to loading the application in the network device. Once added to the network, the resources available through the new application are made available to the user through GUI  895  and the user may establish threshold evaluations as described above through the Threshold dialog box. For example, a new type of forwarding card (e.g.,  552   a,    FIG. 65 ) that is capable of transmitting network traffic in accordance with the MPLS protocol may be added to network device  540 . To allow threshold evaluations of MPLS resources, a new MPLS driver (e.g.,  419   a ) is linked with TML  1046  when the MPLS driver is built and prior to loading the MPLS driver into network device  540 . Once loaded, GUI  895  will show the new board as present in the network device mimic  896   a  ( FIG. 66   a ) and MPLS related tabs (e.g., MPLS interfaces) will be added to status window  897 . The user may select an MPLS interface from an MPLS interfaces tab and then select Threshold menu option  1054  as described above with respect to ATM interfaces. Consequently, changes to or newly added applications are independent of the TML and changes to the TML are independent of the applications with the exception that the applications need to be re-linked with the TML if either are changed. 
   Flexibility is also added by allowing users to evaluate any resource attribute within the network device against a threshold rule. This is possible because when a user selects a resource, the data sent from the NMS client to the NMS server includes the resource&#39;s unique LID or PID. Since each resource may be uniquely identified, each resource attribute may also be checked against a threshold rule. For example, a user may want to be notified if a power supply within the network device fails within a sampling period of every 6 hours. Since the power supply has a unique PID and may be selected by the user in GUI  895 , the user may establish this threshold evaluation. As another example, a network manager may have noticed that nightly backups scheduled for 2:00 am are not being completed. For each virtual connection through which the backups are normally completed, the network manager may establish a threshold evaluation to determine whether other traffic is present on these connections at that time of night. In addition, if excess traffic were present on those connections, since each resource may be associated with one or more customer groups, the network manager would be able to determine which customers were using those connections at that time and whether they had paid for such service. As yet another example, a network manager may wish to know how often automatic protection switching is executed—that is, how often a primary module fails over to a backup module. The TML may be linked into the automatic protection switching application and since each module includes a unique PID, the network manager is able to establish a threshold evaluation to make the necessary determination. 
   Power Distribution 
   Typically, telecommunications network devices include a central power supply system or a distributed power supply system. A central power supply system includes a centrally located power supply that receives power feeds (AC or unregulated DC) from an external source, converts the raw power into regulated voltages (e.g., 5 v, 3.3 v, 1.5 v, 1.2 v) and then distributes the regulated voltages through a backplane or midplane to the appropriate modules in the network device. A distributed power supply system includes power supply circuitry on each module needing power. Unregulated DC power feeds from an external source or sources are connected to filters in the network device and from the filters the unregulated power is distributed to each module in the device needing power. The power supply circuitry on each module then converts the unregulated power into the regulated voltages necessary for that particular module. The filters are used primarily to meet emissions requirements and also provide some protection against external noise. 
   For fully configured/loaded network devices a central power supply system is often less expensive than a distributed power supply system. For network devices that may be configured/loaded over time—that is, modules may be purchased as network demands increase—the distributed power supply system reduces the cost of the base network device by pushing the cost of the power supply onto each module. Distributed power supply systems also allow for more variation in the types of components used and the voltages required by those components since the power supply circuitry on each module can be designed to provide the particular voltages required by the module. The central power supply usually cannot supply all necessary voltages without consuming extensive backplane/midplane routing space. 
   In addition, a new module requiring unique voltages may be added to a distributed power supply system since the power supply circuitry on the module itself is designed to provide the unique voltages. Such a module cannot be added to a network device with a central power supply system without either modifying the central power supply to provide the additional voltages and then building a new backplane/midplane to deliver the new voltages or implementing a distributed power supply on the new module to convert an available voltage from the existing central power supply into the needed voltages. The additional distributed power supply, however, will increase the cost and consume more space and power. Each power supply (i.e., the central and distributed power supply) consumes power: typically, 10–20% is consumed in each power supply. The increase in power consumption also leads to an increase in heat dissipation, which may result in thermal problems. 
   Distributed power supply systems may also improve network device reliability and availability since the power supply circuitry is located on multiple modules—that is, if the power supply circuitry of one module fails, it will not affect the remaining modules. If a central power supply is used, a more complicated redundancy scheme is required, which usually results in lower reliability. In either case, whether a central power supply system or a distributed power supply system is chosen, a network device generally includes an identical, redundant power supply system to increase reliability and availability, and the redundant power supply is preferably attached to a separate external power source. 
   Many network devices include central power supply systems that are removable. Thus, one advantage to such a central power supply system is that if one system fails it may be removed and replaced while the other power supply system continues to function. Unfortunately with distributed power supply systems, the connections to the external raw power source and the filters used to reduce noise are fixed, perhaps through rivets, to the network device chassis. As a result, these components are not replaceable, and if one of these components needs to be replaced, the network device must be shut down. Network service providers are generally required to provide five 9&#39;s availability or 99.999% network up time. Shutting down a network device to replace failed power supply components directly impacts the network device&#39;s availability. 
   As network devices have become larger, multiple power feeds have been required. In such instances, central power supply systems include multiple, independent central power supply subsystems each connected to a separate power feed and each separately removable from the network device. The independence of each subsystem increases the network device&#39;s reliability and availability. However, each of these units generally requires considerable space within the network device, which may reduce the number of functional modules that may be included in the network device. 
   In recent years, deregulation has forced incumbent telecommunications companies to lease out space to competitors. The equipment owned by the different companies within these sites is generally kept in separate locked cages. Consequently, a competitor may not have access to the site&#39;s power source circuit breakers. In response to this situation, many network device providers connect a circuit breaker to each power feed and expose the circuit breaker switch to allow network managers to switch off the power delivered to the device when necessary. Each circuit breaker switch, however, requires a large amount of space (e.g., 3 by 4 inches) on the front or back of the device and may reduce the number of functional network modules that may be included in the device. 
   In one embodiment, network device  540  ( FIG. 2   a ) includes a distributed power supply system. External power feeds from external power sources are connected to the network device through power entry (PE) unit  1060  ( FIG. 41   c ). In one embodiment, PE unit  1060  includes two independent, removable, redundant power distribution units (PDUs)  1062   a  and  1062   b  ( FIGS. 72   a  and  72   b ). Only PDU  1062   a  is shown for convenience. It should be understood, however, that PDU  1062   b  is identical to PDU  1062   a.  Each PDU is inserted within a separate slot  1064   a  and  1064   b  ( FIG. 73   a ) in chassis  620 . 
   Each PDU  1062   a,    1062   b  includes a faceplate  1066  and a cover  1068  ( FIG. 72   a ). The faceplate will be exposed on the rear of the chassis when the PDU is inserted in one of the chassis slots  1064   a  or  1064   b.  In one embodiment, each PDU  1062   a,    1062   b  receives power from five power feeds through connectors  1070   a – 1070   j  extending from faceplate  1066 , where each power feed is connected to two connectors (e.g.,  1070   a  and  1070   b ). The faceplate also includes an on/off toggle switch  1072 . Including five power feeds in one replaceable PDU provides a higher power density (Amps/cubic inch) over systems that include replaceable sub-systems for each power feed. For example, each PDU  1062   a  and  1062   b  may be 17×9×2.25 inches (i.e., 344 cubic inches) and connected to five 60 Amp power feeds such that each PDU provides 300 Amps of power in a very small amount of space for a total power density of 0.87 Amps/cu. in. 
   As can be seen with cover  1068  removed ( FIG. 72   b ), each PDU  1062   a,    1062   b  includes independent filter circuitry  1074   a – 1074   e.  Each filter is connected to a pair of connectors and to an independent circuit breaker/motor combination device  1076   a – 1076   e.  For example, filter  1074   a  is connected to connectors  1070   i  and  1070   j  and circuit breaker device  1076   a.  On/off toggle switch  1072  is connected to on/off logic circuitry  1078  (partially shown) which is connected in series with each of the circuit breaker/motor devices  1076   a – 1076   e.  When on/off toggle switch  1072  is toggled from on to off or off to on, the switch sends signals to each of the circuit breaker/motor devices  1076   a – 1076   e  to cause the motor to physically switch the circuit breaker from on to off or off to on, respectively. Thus, power delivery to the network device through each of the five power feeds of one PDU is controlled by a single on/off toggle switch. 
   In one embodiment, the filter circuitry is an EMI filter part number A60SPL0751 from Aerovox EMI Filters Corporation in El Paso, Tex., and the circuit breaker/motor combination device is a magnetic/hydraulic circuit breaker part number CA1-X0-07-503-321-C from Carlingswitch Corporation in Plainville, Conn. Each circuit breaker/motor device also monitors the voltage it receives from the power feed to which it is connected. If the voltage falls outside a predetermined range, for example, lower than 37.5 v or higher than 75 v, then the circuit breaker/motor device automatically switches to an off position. This allows the power distribution unit to also function as a power controller unit. If the on/off switch is in an on position and one of the circuit breaker/motor devices switches to an off position, on/off logic circuitry  1078  causes a light emitting diode (LED)  1100   a – 1100   e  ( FIG. 72   a )—corresponding to the off circuit breaker—on faceplate  1066  to be illuminated. Alternatively, switches may be used instead of the circuit breaker/motor combination devices. The circuit breaker device is preferred, however, since the circuit breaker provides protection against certain failures within the network device. 
   The single on/off switch does not allow the circuit breakers for each power feed to be independently controlled. However, the single on/off switch does eliminate the need to expose the circuit breaker for each power feed on faceplate  1066 , which significantly reduces the surface area of the network device consumed for power distribution. Since the surface area of network devices is limited, many network devices do not include on/off switches and external circuit breakers must be toggled to provide and remove power from the power feeds connected to the network devices. In a telecommunications site where access to such external circuit breakers is limited, arrangements must be made with the facilities owner to schedule service times, often a difficult arrangement since the facilities owner is usually an incumbant carrier (i.e., a competitor). Ability to turn power off may be required for device reconfigurations, upgrades, or in the event of catastrophic failure (i.e., a fire). Thus, an on/off switch provides the benefit of allowing direct control over power application to the network device, and connecting many circuit breakers within the network device to one on/off switch reduces the network device surface space required for power distribution. Reducing the surface space required may allow additional functional modules to be contained within the network device which generally allows the network device to have increased network service capacity. 
   Each circuit breaker/motor device  1076   a – 1076   e  includes two bus bar connectors  1080   a – 1080   j  which extend from cover  1068  ( FIG. 72   a ) to allow them to be connected with bus bars  1086   a – 1086   j  ( FIGS. 73   a  and  73   c ) mounted on an insulation board  1084 . For example, circuit breaker/motor device  1076   a  is connected to connectors  1080   a  and  1080   b  which are connected to bus bar  1086   i  if the PDU is inserted in slot  1064   a  or bus bar  1086   j  if the PDU is inserted in slot  1064   b.  The insulation board is mounted within chassis  620  adjacent to and below the lower midplane  622   b.  The bus bars and bus bar connectors provide direct, blind mating connections for the multiple power feeds on each PDU. 
   The bus bars are used to distribute power through the midplanes to each of the modules requiring power that are plugged into connectors (see  FIG. 42 ) on the midplanes. Bus bars  1086   a  and  1086   b  are connected with bus bars  1082   a  and  1082   b,  respectively, on the lower midplane which are connected with bus bars  1088   a  and  1088   b,  respectively, on the upper midplane  622   a.  Similarly, bus bars  1086   e,    1086   f,    1086   i  and  1086   j  are connected with bus bars  1082   c,    1082   d,    1082   e  and  1082   f,  respectively, on the lower midplane which are connected with bus bars  1088   c,    1088   d,    1088   e  and  1088   f,  respectively, on the upper midplane. The bus bars on the midplanes are connected using metal straps  1089  ( FIG. 73   b ). Bus bars  1086   c,    1086   d,    1086   g  and  1086   f  are connected with etches (not shown) located on internal layers within the lower midplane which are then connected with etches (not shown) located on internal layers within the upper midplane. 
   Bus bar connectors on the PDU inserted in upper chassis slot  1064   a  connect to bus bars  1086   a,    1086   c,    1086   e,    1086   g  and  1086   i,  while bus bar connectors on the PDU inserted in lower chassis slot  1064   b  connect to bus bars  1086   b,    1086   d,    1086   f,    1086   h  and  1086   j.  Thus, there are five redundant bus bar pairs, for example, bus bars  1086   a  and  1086   b  are a redundant pair as are bus bars  1086   c  and  1086   d,    1086   e  and  1086   f,    1086   g  and  1086   h  and  1086   i  and  1086   j.  Each module requiring power receives power through connectors on one or both of the midplanes from a redundant bus bar pair. In one embodiment, one bus bar pair is dedicated to each quadrant, for example, bus bar pair  1086   a  and  1086   b  may be dedicated to supplying power to modules inserted in quadrant two, and the fifth bus bar pair provides power to modules that are common to all quadrants, for example, switch fabric cards. 
   Referring to  FIG. 74 , for example, a universal port (UP) card  556   h  receives power from redundant bus bar pair  1088   a  and  1088   b  on input lines  1090   a  and  1090   b,  respectively. Input lines  1090   a  and  1090   b  are connected to fuses  1092   a  and  1092   b,  respectively, and the outputs of the fuses are connected to diodes  1094   a  and  1094   b,  respectively. Diodes  1094   a  and  1094   b  are connected to form a diode OR circuit. As a result, a power supply circuit  1096  receives power from whichever diode  1094   a  or  1094   b  provides greater power. Consequently, if either PDU  1062   a  or  1062   b  fails, power supply circuit  1096  will continue to receive power through the diode OR from the other PDU. Power supply circuit  1096  then converts the unregulated DC power received from the diode OR into the particular voltages required by that module, for example, 5 v, 3.3 v, 1.5 v and 1.3 v. Perhaps other voltages may also be provided or perhaps only one or more of these voltages may be provided. 
   The outputs of fuses  1092   a  and  1092   b  may also be sent to a processor component or circuit  1098 . If one of the outputs fails or falls below a predetermined threshold, then the processor may send an error to the network management system such that a network manager may be notified of the failure. 
   Redundant PDUs increase the availability and reliability of the network device. A single, replaceable, multi-feed PDU provides a higher power density than separate replaceable units for each power feed, and a single on/off switch per PDU saves significant surface space on the network device over network devices that provide an on/off switch per power feed. In addition, mounting the filter circuits required for a distributed power supply system in a replaceable PDU allows them to be removed, replaced and/or upgraded along with other power distribution components in the replaceable PDU. For example, if a filter circuit fails, the PDU may be switched off using the toggle switch and removed from the chassis. The removed PDU may be repaired and re-inserted within the chassis or a new PDU may be inserted within the chassis. As another example, if a new filter circuit is designed to provide improved noise reduction or an improved circuit breaker component becomes available, one of the PDUs may be switched off using the toggle switch and replaced with a new PDU including the new filter circuit or circuit breaker. In any case, while one PDU is switched off, the redundant PDU provides power to the network device to keep it running. Once the replaced PDU is up and running, the other PDU may then be switched off and replaced with a new PDU including the new filter circuit or circuit breaker. Similar upgrades may be made for the other PDU components. 
   Common Command Interface 
   To allow for the increased flexibility associated with multiple command interfaces (e.g., command line interface (CLI), web interface, etc.) while minimizing the burden to maintain commands across those interfaces, a common command interface (CCI) is provided. Referring to  FIG. 80 , preferably, the CCI is a distributed application including a central Command Daemon  1108  and distributed command proxies  1110   a – 1110   n.  A command proxy  1110   a – 1110   n  is executed on each card, which includes a processor, in network device  540 . For convenience, only external processor card  542   b,  internal processor card  542   a,  port card  554   a,  and forwarding cards  546   a  and  552   a  are shown in  FIG. 80 . It should be understood, however, that network device  540  may include many other cards, for example, those cards shown in  FIGS. 41   a  and  41   b,  and that each of those cards (except the fan trays (FT), power entry (PE) and MI card  621 ) executes a command proxy. 
   Although Command Daemon  1108  may be executed by any card (including a processor) in network device  540 , it is preferable to execute the Command Daemon on the card through which commands will be received by command interfaces or, where multiple cards may receive commands, the one most likely to have the largest volume. In this example, each of the cards in network device  540  includes a serial port. Thus, each of these cards may receive commands from a CLI interface. However, the majority of commands from command interfaces will likely be received by external processor card  542   b,  and thus, in this example, the Command Daemon is executed by external processor card  542   b.  A backup Command Daemon may be executed by external processor card  543   b.    
   External processor card  542   b  also executes a web server  1112  and a telnet server  1114 . The web server is capable of communicating with an external web browser  1116  to receive commands from a user through a web interface. The telnet server is capable of communicating with an external telnet application  1118  or console  1119  to receive commands from a user through a CLI interface. Each of the other cards may also execute a web server and a telnet server. 
   When a telnet server (e.g.,  1114 ) receives a command from a telnet application (e.g.,  1118 ), the telnet server spawns a child telnet server (e.g.,  1114   a ), which spawns a CLI shell (e.g.,  1120 ). If another command is received, the telnet server spawns a second child telnet server, which spawns a second CLI shell. Thus commands may be received simultaneously from multiple telnet applications. 
   Referring also to  FIG. 81 , commands (e.g.,  1111   a,    1111   b ) received by a web server (e.g.,  1112 ) and/or a telnet server/CLI shell (e.g.,  1114   a / 1120 ) are sent to a local command proxy (e.g.,  1110   a ). The received command includes a unique location identification for the application to which the command is being sent. The web server or CLI shell adds an interface type (e.g., web, CLI) to the command and the message to the command proxy includes the process identification for the server/shell (e.g., web server  1112 , CLI shell  1120 ) sending the message. If the location identification in the command corresponds to a local application (e.g., MKI  50   p,  slave MCD  39   p,  slave SRM  37   p ), then the command proxy sends (arrow  1113   a ) the command to the local application. If, however, the location identification in the command does not correspond to a local application—that is, it corresponds to an application (e.g.,  415   a ) running on another card (e.g.,  554   a )—the command proxy (e.g.,  1110   a ) sends (arrow  1113   b ) the command to Command Daemon  1108 . Using the location identification, the Command Daemon then sends (arrow  1113   c ) —over, for example, internal Ethernet  32  (FIG.  1 )—the command to the command proxy (e.g.,  1110   c ) that is local to that corresponding application (e.g.,  415   a ) and that command proxy sends (arrow  1113   d ) it to the application. 
   Referring also to  FIG. 82 , each application (e.g., Slave SRM  37   a ) capable of responding to a command from a command interface includes one or more command call back routines (e.g.,  1126   a – 1126   n ) and links in a command API  1122  and a display API  1130 . In one embodiment, the command API includes a component registration routine  1124  and a debug command registration routine  1125 . Each application may include one or more components and associated commands. For example, System Resiliency Module (SRM) slave  37   a  (described above) may include a main slave SRM component and commands associated with the slave SRM and may include other components and associated commands such as an SNMP component and associated SNMP commands executable by the slave SRM application. 
   When an application is first loaded or initialized on network device  540 , the application calls component registration routine  1124 . The application includes a component tag (e.g., srms, snmp) in the call and, if the component is associated with commands that are accessible from a web interface, a component title (e.g., Slave SRM, SNMP) is also included in the call. For each component, the component registration routine creates a component data structure (e.g.,  1127 , only one is shown for convenience) including the component tag, the component title and a location identification. The component data structure also includes a command list, and the component registration routine inserts an index command in the command list. Web browsers may send the index command to the web server to retrieve and display to the user a list of commands associated with the component. 
   If there is only one instantiation of an application in the entire network device, the component registration routine may include a location identification or may not include a location identification in the component data structure or may include a “null” value for the location identification. If, as in most cases, however, there are multiple instantiations of an application within the network device, a location identification is included in the component data structure to allow the command proxy and the command Daemon to uniquely identify and send commands to each application within network device  540 . As specified by the application writer within the application, the location identification may be based on the slot within which the card executing the application is located, the application&#39;s process name and slot, or a programmable tag designed by the application writer. For example, only two instantiations of Global Log Service  1044  ( FIG. 65 ) may be running in network device  540 : a primary and a backup. In this case, a programmable tag within the Global Log Service may instruct the component registration routine to use the primary or backup indication provide by the local slave SRM as the location identification. As another example, one instantiation of the slave SRM application may be running on several cards in the network device. In this case, then the application may instruct the component registration routine to use the slot label in which the card executing the slave SRM is inserted as the location identification. As yet another example, multiple instantiations of a device driver may be running on the same card. In this case, the application may instruct the component registration routine to use the slot label and each device driver&#39;s unique process name, for example, listed in PMD file  48  ( FIG. 13   a ), as the location identification for each device driver. 
   After the component registration routine has created a component data structure, the application calls command registration routine  1125 . For each command provided by the application for the corresponding component, the command registration routine creates a command data structure including a command tag, a command title (for use by a web server), a command description for a help service and for display on a web server, command flags, a handle corresponding to a call back routine (e.g.,  1126   a – 1126   n ) within the application and a context argument to be sent to the call back routine when the command is executed. For example, the slave SRM applications may be capable of executing a command to reset the slot. The command tag for this command may be “resetme”, the command title may be “Reset Slot” and the command description may be “Use to reset the slot”. Flags are command options. For example, if the command were only possible from a particular command interface, such as the CLI, the flag may indicate this so that it is not displayed on the web interface. The context argument may include data to be used by the call back routine when the command is executed. Other information may also be included in the command data structure, for example, a security level argument indicating the minimum level of security clearance a user must have in order to execute the command. Once the command data structure for a command is complete, the command registration routine attaches the command data structure to the command list in the component data structure. 
   The command API within each application registers with its local name server (e.g.,  220   a – 220   n,    FIG. 16   c ) for access to its local command proxy. When an application is first initialized and the local name server notifies the command API of the local command proxy&#39;s process identification, the command API registers each debug command for each component with the local command proxy. For each command, the command API sends a registration message to the local command proxy including a “debug” label, the component tag, the location identification, and the command tag, description, title, and flags. The debug label, component tag and command tag may be combined to form a full command string. The registration message itself, like all messages, includes the process identification of the application (including the command API) that sent the registration message. The local command proxy saves the information provided in the registration message and the process identification of the application that sent the message. 
   In addition to the debug commands described above, other groups of commands may also be registered by an application. For example, one or more applications may contain and register “operational” commands. Operational commands may include network device monitoring commands (e.g., show commands), basic network device maintenance commands (e.g., boot) and, perhaps, configuration commands (e.g., configure SONET path). The debug and operational commands may have some overlap and a common command may share a call back routine within an application. 
   To register operational commands, the application calls an operational registration routine  1134 , which creates an operational data structure  1135 . The operational registration routine includes an operational tag and a location identification within the operational data structure. The operational data structure also contains a command list. Once the operational data structure is complete, the application calls an operational command registration routine  1137 . For each operational command executable by the application, the operational command registration routine creates a command data structure including a command tag, a command title if the command is accessible by a web server, a command description for a help service and a web server, a call back routine handle pointing to the call back routine within the application and a context argument to be passed back to the call back routine when the command is executed. The command data structure may include additional information, such as a timeout value within which execution of the command must be complete, help text and a security level. Once the command data structure is complete, the operational command registration routine attaches it to the command list within the operational data structure. 
   When an application is first initialized and the local name server notifies the command API of the local command proxy&#39;s process identification, the command API also registers each operational command with the local command proxy. For each command, the command API sends a registration message to the local command proxy including the location identification of the application and the command tag, description, title, and flags. The registration message may also include an “operational” label. Again, the local command proxy saves the information provided in the registration message and the process identification of the application that sent the registration message. 
   Other groups of commands may be similarly registered. Since registering operational commands is similar to registering debug commands, in an alternative embodiment, component registration routine and operational registration routine may be combined into one registration routine and debug command registration routine and operational command registration routine may be combined into one command registration routine. 
   Each local command proxy registers with its local name server for access to Command Daemon  1108 . When a name server provides a command proxy with the process identification of the Command Daemon, the command proxy registers with the Command Daemon each of the commands registered with it by local applications. For each command, the registration message from the command proxy to the Command Daemon includes all the information saved for that command by the command proxy except the process identification of the application that registered the command. The Command Daemon then saves the registration information in the registration message and the process identification of the command proxy that sent the registration message. The command proxy may register commands in a variety of ways. For example, a command proxy may send one registration message for each command, one registration message for each fall command string and include each location identification associated with that command string, or one registration message including all the commands it has registered. 
   As previously mentioned, a backup Command Daemon may be running on backup external processor card  543   b.  Each command proxy may register its commands with both the primary and backup Command Daemons such that on fail over, the backup Command Daemon simply takes over. Preferably, however, the command proxies only register with the primary Command Daemon, and upon a fail over from primary external processor card  542   b  to backup external processor card  543   b,  each command proxy re-registers its commands with the Command Daemon running on the backup (now primary) external processor card  543   b.    
   If subsequent to initialization, new commands are registered, for example, by new applications being initialized or existing applications registering new commands, the command proxies register these new commands with the Command Daemon as well. In addition, an application may cause the command API to de-register a command with the local command proxy, for example, if a particular service is changed or removed from the network device configuration. Such a command de-registration may cause the command proxy to remove the command registration information from its list and to de-register that command with the Command Daemon. Moreover, if an application ceases to exist (e.g., crashes), the command proxy may remove all commands registered by that application and de-register those same commands with the Command Daemon. Similarly, if a card is removed from the network device or crashes, the Command Daemon may de-register all commands registered by the local command proxy that was running on that card. In addition, if a command proxy fails, upon restart of the command proxy, the local name server will notify each registered command API of the process identification of the re-started command proxy and the command APIs will re-register the application&#39;s commands with the re-started command proxy. 
   Although a distributed application is preferred, the CCI need not be a distributed application. In this case, the CCI would include only the Command Daemon, and each application on each card in the network device would register its commands directly with the Command Daemon. In addition, the web server and each telnet server would send commands directly to the Command Daemon, which would forward the received commands directly to the appropriate applications. 
   Referring again to  FIGS. 80 and 81 , when a command (e.g.,  1111   a,    1111   b ) is received by a web server (e.g.,  1112 ) or a telnet server/CLI shell (e.g.,  1114   a / 1120 ) and then sent to a command proxy (e.g.,  1110   a ), the command proxy determines if the command corresponds to a local application by comparing the received command string to the command strings that it has saved for registered commands. For debug commands, the full command string includes the debug label, component tag and command tag, and for operational commands, the full command string may include only the command tag or, perhaps, an operational label and the command tag. If no match is found, the command proxy forwards the command to the Command Daemon. If a match is found, the command proxy compares the location identification in the received command to the one or more location identifications associated with the matched command string. If there is a match, then the command proxy sends the command to the application that registered the command using the process identification saved with the matching command string and location identification. If there is no match, then the command proxy sends the command to Command Daemon  1108 . 
   When the Command Daemon receives a command, it compares the full command string to its list of registered commands. If no match is found, an error message is sent back to the web server or CLI shell that sent the command (i.e., originating server). If a match is found, then the Command Daemon compares the received location identification to the one or more location identifications associated with that match. Again, if no match is found, then the Command Daemon sends an error message to the originating server. If a match is found, then the Command Daemon forwards the command to the command proxy using the process identification saved with the matching command string and location identification. 
   That command proxy then compares the received full command string to its list of saved commands. If no match is found an error message is sent to the originating server. If a match is found, the command proxy compares the location identification in the received command to the one or more location identifications associated with the matched command string. Again, if no match is found an error message is sent to the originating server. If a match is found, the command proxy forwards the command to the application that registered the command using the process identification saved with the matching command string. 
   In one embodiment, under certain circumstances, a command may be sent without a location identification. For example, no location identification may be sent if the command is associated with only one application running on the card that initially receives the command or if the command is associated with one application in the entire network device. As described above, when a command is received, the local command proxy compares the received command string to the command strings that it saved for registered commands. If a match is found and is associated with multiple location identifications, then an error message is returned to the originating server. If a match is found with only one location identification, then the command proxy forwards the command to the application that registered that command using the process identification saved with the command. If no match is found, then the command proxy forwards the command to the Command Daemon. If the Command Daemon finds no match or a match with multiple associated location identifications, it sends an error message to the originating server. If the Command Daemon finds a match with one location identification, then the Command Deamon sends the command to the command proxy that registered the command using the process identification saved with the matching command. That command proxy then forwards the command to the appropriate application. 
   Referring again to  FIG. 82 , command API  1122  within each application also includes a command handler  1128 . When a command is received by an application from the local command proxy, the command handler sends a message to a display API  1130  including the process identification included in the received command of the originating server. If the interface type in the received command indicates that the originating server is a web interface, then the command handler also includes instructions to send any display data generated by a call back routine in response to the command to the originating server in HTML format. The command handler also determines—using the component data structure or operational data structure—the call back routine handle associated with the received command and then calls that call back routine providing any context argument included within the received command. 
   When the call back routine (e.g.,  1126   a ) is executed, if it produces data (i.e., display data) to be sent to the originating server, the call back routine calls appropriate routines within display API  1130  and provides the display data. For example, if header information is to be displayed, the call back routine calls a header routine within the display API. The display routine then sends the data directly to the originating server using the process identification provided by the command handler. For responses to the web server, the display routine provides the display data in HTML format. 
   Once the command is executed, the call back routine notifies the command handler, which sends a restore message to a completion display routine within the display API. In response, the display routine sends a completion response to the originating server. With respect to the CLI interface, the completion response causes the CLI prompt to return. With respect to the web server, the completion response may cause the web browser to provide a completion indication to the user. 
   Although the CCI has been described as receiving commands from a web interface and a CLI interface, it should be understood that other command interfaces are possible, including, for example, a network/element management system interface. For each different interface, an internal server for that interface would simply need to be capable of sending commands to a local command proxy including a server type. In many instances, adding a new interface may not even require that the command handler be upgraded so long as the commands received included information sufficient for the command handler to instruct the display API as to how to format any display data. 
   In order to understand the significance of the Common Command Interface (CCI), note that call back routines included in the applications are shared across command interfaces. The command API provides a command interface abstraction. A new application may be dynamically added (including new applications associated with newly added hardware) and existing applications may be dynamically upgraded or removed while the network device is operating and any new or modified commands will be registered and any old commands will be de-registered. Since the call back routine(s) for each command are shared across command interfaces, a single change is applied to all interfaces, and the command proxy and Command Daemon software need not be modified. 
   Referring to  FIG. 83 , in an alternative embodiment, the Common Command Interface is extended beyond a single network device to a group of connected network devices (e.g.,  540 ,  540   a – 540   n ) and includes a Community Command Daemon  1140 . The Community Command Daemon may run on any of the connected network devices (e.g.,  540 ) or on a separate connected device (not shown). After the command proxies (e.g.,  1110   a – 1110   n,    1142   a – 1142   n,    1144   a – 1144   n,    1146   a – 1146   n ) register their commands with the Command Daemon (e.g.,  1108 ,  1108   a – 1108   n,  respectively) running within their network device (as described above), each Command Daemon registers its commands—all or a subset—with the Community Command Daemon. During this registration, each Command Daemon attaches a network device identifier to each command registration message sent to the Community Command Daemon to allow the Community Command Daemon to associate registered commands with each Command Daemon. 
   In one example, the network device identifier is the Media Access Control (MAC) address assigned to the card executing the Command Daemon. Since the card (e.g., external processor card  542   b ) executing the Command Daemon may fail over to a backup card (e.g., external processor card  543   b ), the MAC address associated with the Command Daemon may change. To prevent this, preferably, the network device identifier is a unique global identifier for the network device. As described above in the section entitled “Network Device Authentication”, the logical identifier (LID) in column  1014   a ′ ( FIG. 64 ) of Administration Managed Device table  1014 ′ provides a global identifier for each network device in the network. Since the Administration Managed Device table is maintained on the NMS database, the Command Daemon would retrieve the LID associated with its network device prior to registering its commands with Community Command Daemon  1140 . 
   It will be understood that variations and modifications of the above described methods and apparatuses will be apparent to those of ordinary skill in the art and may be made without departing from the inventive concepts described herein. Accordingly, the embodiments described herein are to be viewed merely as illustrative, and not limiting, and the inventions are to be limited solely by the scope and spirit of the appended claims.