Abstract:
A distributed control system architecture (HSE) provides an open, interoperable solution optimized for integration of distributed control systems and other control devices in a high performance backbone, provides an open, interoperable solution that provides system time synchronization suitable for distributed control applications operable over a high performance backbone, and provides an open, interoperable solution that provides a fault tolerant high performance backbone as well as fault tolerant devices that are connected to the backbone. The distributed control system architecture comprises a High speed Ethernet Field Device Access (HSE FDA) Agent, which maps services of a distributed control system, e.g., a fieldbus System, to and from a standard, commercial off-the-shelf (COTS) Ethernet/Internet component. The distributed control system architecture also comprises a High speed Ethernet System Management Kernel (HSE SMK) that operates to keep a local time, and keeps the difference between the local time and a system time provided by a time server within a value specified by the time sync class. The local time is used to time stamp events so that event messages from devices may be correlated across the system. The distributed control system architecture further comprises a High speed Ethernet Local Area Network Redundancy Entity (HSE LRE) that provides redundancy transparent to the applications running on the system. The HSE LRE of each device periodically transmits a diagnostic message representing its view of the network to the other Devices on the system. Each device uses the diagnostic messages to maintain a Network Status Table (NST), which is used for fault detection and selection from a redundant pair of resources.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part (CIP) application of U.S. application Ser. No. 08/916,178 filed Aug. 21, 1997, and is related to and claims priority from U.S. Provisional Application No. 60/024,346 filed Aug. 23, 1996, and U.S. Provisional Application No. 60/139,814 filed Jun. 21, 1999, all of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to control system architecture. More particularly, the present invention relates to an open, interoperable distributed control system in a high performance network environment. 
     BACKGROUND OF THE INVENTION 
     Automatic control systems are critical to all sectors of industry such as process control, discrete control, batch control (process and discrete combined), machine tool control, motion control, and robotics. One of the strongest needs in modern control systems is development and use of “open” and “interoperable” systems. Open, interoperable systems allow control devices made by different manufacturers to communicate and work together in the same system without the need for custom programming. “Fieldbus” is the common term used to describe these types of control systems. 
     The movement toward open, interoperable fieldbus systems is driven by device manufacturers and end users. Manufacturers want open, interoperable systems because it allows them to sell their products to more end users while reducing development costs. End users want open, interoperable systems so that they can select the best control devices for their system regardless of the device manufacturer. 
     There has also been a trend toward distribution of control functions into intelligent devices. In centralized control systems, a central controller performs all the control functions. 
     In distributed control systems, more than one control device operating in the system takes an active role in the control functions. Although both centralized and decentralized systems use a communication network, decentralized systems reduce overall system costs by reducing or eliminating the centralized controller functions between the control devices and the human-machine interface. 
     In order for distributed control systems to be truly open and interoperable, both the communications system and the user layer (above the communication system layers) must be specified and made open. One of the truly open and interoperable distributed systems is the fieldbus system provided by the Fieldbus Foundation. The FOUNDATION™ fieldbus user layer is described, e.g., in U.S. patent application Ser. No. 08/916,178 (hereafter the “178” application) filed Aug. 21, 1997,entitled “BLOCK-ORIENTED CONTROL SYSTEM”, and assigned to the assignee of the present application. 
     The lower speed 31.25 kilobits per second fieldbus (H1) used by the FOUNDATION™ fieldbus is described in part by International Electrotechnical Committee (IEC) Standard IEC 61158, the entirety of which is hereby incorporated by reference herein. 
     While the FOUNDATION™ fieldbus provides the open and interoperable solution for the H 1  control capability, there is a great need to provide an open and interoperable solution for distributed control on a very high performance communication system typically called a fieldbus “backbone” network. The backbone network aggregates information from the lower speed control devices, e.g., the H 1  and other control devices, which is used in supervisory and advanced control applications. The backbone is also needed for integration of control information into the enterprise&#39;s Management Information Systems (MIS). 
     One of the widely accepted standards for high performance communications signaling is Ethernet. Invented by Xerox in the 1970&#39;s, Ethernet has progressed from an initial speed of 10 Megabits per second, to 100 Megabits per second, to 1 Gigabit per second and beyond. Ethernet signaling is specified in an Institute of Electrical and Electronics Engineers (IEEE) standard (IEEE 802.3). Ethernet signaling is the underlying technology used by the Internet. The Internet protocols are specified by the Internet Engineering Task Force (IETF) and are issued as Request For Comment (RFC) specifications. 
     Although Ethernet/Internet technology provides the basic services for a high performance fieldbus backbone, it does not provide for all of the functions needed for use in distributed control systems. In particular, IEEE and IETF do not have suitable open and interoperable solutions for integration of distributed control systems (e.g., the H 1  subsystem), system time synchronization, and fault tolerance. 
     The method of transferring information from lower speed fieldbuses to the Ethernet used by organizations such as Open DeviceNet™ Vendor Association, Inc., (“EtherNet/IP,”) and PROFIBUS International, (“PROFINet”) are not suitable for use in the high performance environment because they encapsulate the lower speed protocol packets in an Ethernet frame. This method, known as “tunneling,” is common in centralized control systems, but is inadequate for high performance distributed control systems. Although simpler to specify, tunneling would require too many Transport Control Protocol (TCP) connections with the resulting interrupt processing and memory overhead on the devices connected to the fieldbus backbone. In addition tunneling wastes much of the Ethernet bandwidth because the lower speed protocol packets (e.g., the H 1  packets) are small and in many cases the Ethernet packet overhead would be bigger than a lower speed protocol packet. 
     Devices connected to the Ethernet must have a common sense of system time for time stamp and function block scheduling (control) purposes. For high performance distributed control, system time often needs to be accurate to within less than 1 millisecond. Heretofore, there is no known solution that provides this accuracy using the Commercial Off The Shelf (COTS) Ethernet equipment. 
     Fault tolerance of the Ethernet communication media and devices connected to the Ethernet is required for high performance distributed control applications. There is no known solution that provides the required fault tolerance using standard COTS Ethernet equipment. All of the prior attempts in providing the required fault tolerance require special Ethernet/Internet electronic hardware and/or software, and/or a non-standard “redundancy manager” device to be added to the Ethernet. 
     Thus, what is needed is an open, interoperable solution optimized for integration of distributed control systems and other control devices in a high performance fieldbus backbone. 
     What is also needed is an open, interoperable solution that provides system time synchronization suitable for distributed control applications operable over a high performance fieldbus backbone. 
     What is also needed is an open, interoperable solution that provides a fault tolerant high performance fieldbus backbone as well as fault tolerant devices that are connected to the fieldbus backbone. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the shortcomings described above and provides a new and improved distributed control system, which operates on a high performance backbone, e.g., the standard COTS Ethernet and Internet technology. The embodiments of the present invention are collectively referred to herein as the “High Speed Ethernet” (HSE). HSE includes the features of the distributed control system described by the &#39;178 application and FOUNDATION™ fieldbus specifications (which are listed in Appendix A as the Reference Set 1), and further includes three new protocols described in the supporting specifications thereof, which are listed in Appendix A as the Reference Set 2. In particular, the new protocols are referred to herein as: the HSE Field Device Access (FDA) Agent, the HSE System Management Kernel (SMK), and the HSE Local Area Network Redundancy Entity (LRE). 
     The HSE FDA Agent allows System Management (SM) and Fieldbus Message Specification (FMS) services used by the H 1  devices to be conveyed over the Ethernet using standard Internet User Data Protocol (UDP) and Transport Control Protocol (TCP). This allows HSE Devices on the Ethernet to communicate to H 1  devices that are connected via a “HSE Linking Device.” The HSE FDA Agent is also used by the local Function Block Application Process (FBAP) in a HSE Device or HSE Linking Device. Thus, the HSE FDA Agent enables remote applications to access HSE Devices and/or H 1  devices through a common interface. 
     The HSE SMK ensures that system level functions in each device are coordinated. These functions include system time, addition and removal of devices from the network, and function block scheduling. HSE SMK uses local clock that operates to keep a local time, and keeps the difference between the local time and a system time provided by a time server within a value specified by the time sync class (See Reference Set 1 of Appendix A herein). The local time is used to time stamp events so that event messages from devices may be correlated across the system. Local time is also used to schedule the execution of the local function blocks. 
     HSE fault tolerance is achieved by operational transparency i.e., the redundancy operations are not visible to the HSE applications. This is necessary because HSE applications are required to coexist with standard MIS applications. The HSE LRE coordinates the redundancy function. Each HSE Device periodically transmits a diagnostic message representing its view of the network to the other HSE Devices on its Ethernet interfaces (commonly called Ethernet “Ports”). Each device uses the diagnostic messages to maintain a Network Status Table (NST), which is used for fault detection and Ethernet transmission port selection. There is no central “Redundancy Manager”. Instead, each device determines how it should behave in response to faults it detects. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings, in which: 
     FIG. 1 is a block diagram showing an exemplary embodiment of a high performance distributed control system in accordance with the principles of the present invention; 
     FIG. 2 is a block diagram showing an exemplary embodiment of device system architecture of a high performance distributed control system in accordance with the principles of the present invention; 
     FIG. 3 is a block diagram showing an exemplary embodiment of the structure of the High Speed Ethernet Management Information Base of the device system architecture shown in FIG. 2; 
     FIG. 4 is a block diagram showing an exemplary embodiment of the device system architecture shown in FIG. 2, showing the various local interfaces of the High Speed Ethernet Field Device Access agent; 
     FIG. 5 is a block diagram showing an exemplary embodiment of the relevant portions of the high performance distributed control system involved in time synchronization process in accordance with the principles of the present invention; 
     FIG. 6 is a flow diagram illustrative of an exemplary embodiment of the process of time synchronization in accordance with an embodiment of the principles of the present invention; 
     FIG. 7A is a timing diagram illustrative of a starting time offset before the time synchronization process in accordance with an embodiment of the principles of the present invention; 
     FIG. 7B is a timing diagram illustrative of a starting time offset after the time synchronization process in accordance with an embodiment of the principles of the present invention; and 
     FIG. 8 is a block diagram showing an exemplary embodiment of the redundant topology of a high performance distributed control system in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to exemplary embodiments, particularly, with specific exemplary implementations of distributed control system in an Ethernet network. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, other implementations and designs using any other high speed networks, and that any such variation would be within such modifications that do not depart from the true spirit and scope of the present invention. 
     A: HSE Distributed Control System Overview 
     Referring to FIG. 1, an example of a high performance control system  100  is shown where standard COTS Ethernet equipment  130  is used to interconnect HSE Linking Devices  110  and HSE Devices  120  to an Ethernet Network  140 . The HSE Linking Devices  110  in turn connect to H 1  Devices  170  using H 1  Networks  150 . Other types of equipment such as a Personal Computer (PC)  160  may also be connected to the Ethernet Network  140 . 
     The actual Ethernet network topology and COTS Ethernet equipment configuration will depend on the particular application needs. However any Ethernet network topology or configuration using standard COTS Ethernet equipment other than the exemplary topology shown in FIG. 1 may be used, and such variations would be within such modifications that do not depart from the true spirit and scope of the present invention. 
     A.1: HSE System Architecture 
     The HSE system architecture in accordance with an embodiment of the principles of the present invention is shown in FIG.  2 . The HSE system architecture is designed to meet the functional needs of the high performance distributed manufacturing and process control environments, e.g., in a high speed Ethernet network. It permits distributed automation systems to be constructed from various control and measurement devices manufactured by different vendors. The HSE system architecture is described by architecture components that have been adapted to the specifics of both the H 1  and HSE environments. 
     The various protocols and standards referenced in the following disclosure are described in detail in the manuals and specifications listed in Appendix A herein, which are available from the Fieldbus Foundation, a not-for-profit organization headquartered in Austin, Texas, and the respective current versions as of the filing date of the present invention of all of which are hereby incorporated by reference in their entirety herein. Each of the architecture components of the HSE system architecture (shown in FIG. 2) will now be described in more detail. 
     A.2: Function Block Application Process Virtual Field Device (FBAP VFD) 
     Application Process (AP) is a term defined by the International Standards Organization (ISO) Open Systems Interconnect (OSI) Reference Model (RM), ISO 7498, to describe the portion of a distributed application that is resident in a single device. The term is used in the following description to refer to the entities within a device that performs a related set of functions, such as function block processing, network management, and system management. 
     Virtual Field Device (VFD) is a term defined by the Fieldbus Foundation (See Fieldbus Message Specification FF-870 listed in Reference Set 1 in Appendix A herein). A VFD makes the parameters of an AP visible to a communication network. 
     In accordance with the principles of the present invention, the HSE system architecture (shown in FIG. 2) supports the Function Block Application Process Virtual Field Device (FBAP VFD)  260 . The FBAP VFD  260  provides a common means for defining inputs, outputs, algorithms, control variables, and behavior of the automation system. There may be multiple FBAP VFDs  260 , e.g., n FBAP VFDs as shown, in a device in order to satisfy the particular needs an application. The FBAP VFD may or may not be present in an HSE Device or HSE Linking Device. If the HSE FBAP VFD is present, the device is sometimes also referred to as a “HSE Field Device.” In the following descriptions, however, the FBAP VFD is to be assumed to be present in the HSE Device and HSE Linking Device, even if the term “HSE Field Device” is not used. 
     A standard set of function block classes and parameters are defined by the Fieldbus Foundation, e.g., in one or more of the specifications listed in Appendix A herein. Manufacturers of control devices may append their own parameters to the standard set of parameters to accommodate additional function block definitions as new requirements are discovered, and as technology advances. A more detailed description of the function block classes and parameters may be found, e.g., in Function Block Application Process-Part 1 Specification FF-890 listed in Reference Set 1 of Appendix A herein. 
     A.3: H 1  Interface 
     Each H 1  Network  150  attached to a HSE Linking Device  110  (shown in FIG. 1) requires a H 1  Interface  240 . The Bridge  250  is used to convey H 1  Network messages directly between other H 1  Interfaces  240  within the same HSE Linking Device  110  (shown in FIG.  1 ). A HSE Linking Device may comprise, e.g., a HSE Device  120  (shown in FIG. 1) that includes at least one H 1  Interface  240 . 
     A more detailed description of a H 1  Interface may be found in the Fieldbus Message Specification FF-870, Fieldbus Access Sublayer Specification FF-821, Data Link Services and Data Link Protocol Specifications FF-821, 822, and Data Link Protocol Specification for Bridge Operation Addendum FF-806, all of which are listed in the Reference Set 1 of Appendix A herein. 
     A.4: Ethernet/Internet Stack. 
     The HSE system architecture uses a standard COTS Ethernet/Internet (“stack”)  280  for communication with other devices on the Ethernet Network  140 . The Ethernet/Internet stack used by HSE consists of Distributed Host Control Protocol (DHCP)  285 , Simple Network Time Protocol (SNTP)  286 , and Simple Network Management Protocol (SNMP)  287 , which in turn use Transport Control Protocol (TCP)  283  and User Data Protocol (UDP)  284  services. 
     TCP  283  and UDP  284  in turn use the standard Internet Protocol (IP)  282  services, which uses the standard IEEE Ethernet 802.3 Media Access Control (MAC) and Physical (PHY) Layers  281 . The PHY layer in  281  connects to one or more Ethernet Networks  140 . 
     The Internet DHCP, SNTP, SNMP, TCP, UDP and IP protocols are specified by the Internet Engineering Task Force (IETF) Request For Comment (RFC) specifications. The IETF RFCs are listed in Appendix B herein, which are hereby incorporated by reference herein in their entireties. An Institute of Electrical and Electronics Engineers (IEEE) standard (IEEE 802.3), the entirety of which is hereby incorporated by reference herein, describe the Ethernet MAC and PHY layers. The specific use of each layer and protocol are detailed in the Ethernet Presence Specification FF-586 listed in Reference Set 2 of Appendix A herein. 
     By preserving the standard use of the Ethernet/Internet stack, the HSE system architecture ensures interoperability among the different stack manufacturers. 
     A.5: HSE Management Agent 
     Again referring to FIG. 2, in general, the HSE Management Agent  270  uses DHCP  285  for acquiring an IP address for the device, SNTP  286  for maintaining time synchronization with a time server, and SNMP  287  for managing the TCP, UDP, and IP protocol layers. HSE Management Agent use of DHCP, SNTP and SNMP is routine and complies with standard practices known to those familiar with the Internet protocols, e.g., according to IEEE 802.3. 
     The HSE Management Agent uses SNMP  287  for managing the Internet layer protocols. Specifically, the HSE Management Agent  270  provides Ethernet Network access to the standard Management Information Base-II (MIB II) as defined by SNMPv2 in RFC  1213  and RFC  1643  (see Appendix B), and as defined also by Ethernet Presence FF-586 listed in Reference Set 2 of Appendix A herein. 
     In accordance with an embodiment of the present invention, in order to comply with the ISO standards, the HSE Management Information Base (HSE MIB)  271  comprises of a standard part, which is the second version of MIB-II as defined in RFC  1213  and a HSE specific part (which is defined under the private enterprises level). For convenience in understanding, the detailed structure of the HSE MIB  271  is shown in FIG.  3 . The standardized structure of the HSE MIB  271  provides a profile allowing interoperability, making the device appear as a well-behaved node. 
     B: HSE Core 
     Referring again to FIG. 2, the HSE core portion  200  of the HSE system architecture identifies the new HSE capability in accordance with the principles of the present invention. The HSE core  200  provides the essential capabilities and integration needed to realize the high performance distributed control using HSE Devices, HSE Linking Devices and standard COTS Ethernet equipment. 
     B.1: Network Management Agent Virtual Field Device 
     The HSE System Architecture includes a Network Management Agent VFD (NMA VFD)  210  for each HSE Device and each HSE Linking Device. The NMA VFD provides means for configuring, controlling and monitoring HSE Device and HSE Linking Device operation from the network. 
     Management information is contained in the Network Management Information Base (NMIB)  213  and the System Management Information Base (SMIB)  212 . Using the configuration management capabilities of the NMA VFD, parameters are set in the NMIB and SMIB to support data exchanges with other devices in the system. This process involves defining the transfers between devices and then selecting the desired communications characteristics to support the transfers. 
     The NMA VFD can also be configured to collect performance and fault related information for selected transfers. This information is accessible during run-time, making it possible to view and analyze the behavior of device communications. If a problem is detected, performance is to be optimized, or device communications are to be changed, then reconfiguration can be performed dynamically while the device is still operating. 
     NMA VFD parameters and behavior are further defined in the HSE Network Management Specification FF-803 listed in the Reference Set 2 of Appendix A herein. 
     B.2: HSE Field Device Access Agent 
     The HSE Field Device Access (FDA) Agent will now be described with References to FIG. 4, which is the same figure as FIG. 2 except that Local Interactions ( 291 - 299 ) for the HSE Field Device Access (FDA) Agent  290  are shown. The operation of the HSE FDA Agent will now be described in terms of these local interactions. 
     One of the main functions of the HSE FDA Agent  290  is to map services already defined for FOUNDATION™ fieldbus System Management (SM) (See FF-880 listed in the Reference Set 1 of Appendix A herein) and Fieldbus Message Specification (FMS) (See FF-870 listed in the Reference Set 1 of Appendix A herein) to and from the standard, COTS Ethernet/Internet  280  component. 
     Generally, the HSE FDA Agent  290  emulates the mapping defined by the FOUNDATION™ fieldbus Fieldbus Access Sublayer specification (See FF-875 listed in the Reference Set 1 of Appendix A herein). The HSE FDA Agent  290  provides the common interface that enables remote applications to access devices of any type on both the H 1  Networks  150  and the HSE Network  140 . 
     Thus the HSE FDA Agent  290  in accordance with the principles of the present invention allows systems to be constructed where the control is distributed in into various HSE Devices and/or H 1  Devices, and any combinations thereof, as needed by the particular end user application. 
     B.2.1: HSE FDA Agent Local Interfaces 
     B.2.1(a): Local Interface  291 : TCP—The TCP local interface  291  allows the HSE FDA Agent  290  to send and/or receive FMS messages using TCP  283 . TCP  283  provides interfaces modeled as sockets through which the HSE FDA Agent  290  submits a buffer that contains one or more messages. 
     B.2.1(b): Local Interface  292 : UDP—The UDP local interface  292  allows the HSE FDA Agent  290  to send and/or receive SM messages and certain FMS messages using UDP  284 . UDP  284  provides interfaces modeled as sockets through which the HSE FDA Agent  290  submits a buffer that contains one or more messages. 
     B.2.1(c): Local Interface  293 : HSE NMIB—The HSE FDA Agent  290  provides a local interface to the HSE NMIB  213  in NMA VFD  210 . The HSE FDA Agent is capable of providing configuration and read-only access to NMA VFD  210  via the HSE NMIB Local Interface  293 . 
     B.2.1(d): Local Interface  294 : HSE SMIB—The HSE FDA Agent  290  provides a local interface to the HSE SMIB  212  in NMA VFD  210 . The HSE FDA Agent  290  is capable of providing configuration and read-only access to NMA VFD  210  via the HSE SMIB Local Interface  294 . 
     B.2.1(e): Local Interface  295 : HSE SMK—The HSE FDA Agent  290  conveys HSE SM services to and from the HSE SMK  220  through the HSE SMK local interface  295 . In accordance with an embodiment of the present invention, in a HSE Linking Device, the HSE SMK  220  communicates locally with each of the H 1  interfaces  240 , and does not use the HSE FDA Agent  290 . 
     B.2.1(f): Local Interface  296 : HSE LRE—The HSE FDA Agent  290  maintains a local interface with the HSE LAN Redundancy Entity (HSE LRE)  230  of the device through the HSE LRE local interface  296 . Use of the HSE LRE local interface  296  will be described in more detail later. 
     B.2.1(g): Local Interface  297 : H 1  Interface—Only HSE FDA Agents  290  of a HSE Linking Device interact with the H 1  Interface(s)  240  to access H 1  Networks  150 . The H 1  local interface provides the HSE FDA Agent with FMS and SM access through the HSE SMK  220 . 
     The HSE FDA Agent forwards FMS requests and responses received from the TCP Interaction  291  and UDP Interaction  292  to Hi Network  150  through the H 1  Interface(s)  240 . The HSE FDA Agent also forwards H 1  requests and responses received from a H 1  Network through the H 1  Interface Interaction  297  to the Ethernet Network  140  using TCP Interaction  291  and UDP Interaction  292 . 
     Thus, the HSE FDA Agent  290  interacts with the services in the H 1  Network in the same manner as any other application program would normally interact with the H 1  network. 
     B.2.1(h): Local Interface  298 : FBAP VFD—The HSE FDA Agent  290  uses the FBAP VFD local interface  298  to access the FBAP VFD  260 . Both FMS and SM messages are communicated using the FBAP VFD local interface  298 . 
     B.2.1(i): Local Interface  299 : HSE Management Agent—The HSE FDA Agent  290  maintains the HSE Management Agent local interface  299  with the HSE Management Agent  270  to access certain Quality of Service parameters associated with its UDP/TCP connections. The use of these parameters by the HSE FDA Agent  290  is local to the specific UDP/TCP implementation. 
     B.2.2: HSE FDA Agent Operation 
     Again referring to FIG. 4, during the configuration of the system, HSE SMK  220  uses the local interface  295  for adding HSE and/or H 1  devices to, and deleting the same from, the distributed system. An exchange of SM messages is used to identify new (or to be deleted) HSE and/or H 1  Devices in the system. 
     For example, after a new HSE Device receives an Internet Protocol (IP) address, the new HSE Device periodically announces its presence on the Ethernet network  140 . HSE Linking Devices also announce changes detected on their H 1  Network  150 . In a similar way, HSE SMK uses the local interface  295  to determine the location of the function block “tags” that might exist in the HSE Devices and/or H 1  Devices. 
     During operation of the system, the data acquisition, display and supervisory control functions, which are typically executing on a Personal Computer (PC) connected to the Ethernet Network  140 , will need to access the data in a HSE Device, a HSE Linking Device and/or H 1  devices connected to the H 1  Networks  150 . The data access is typically performed using the “Client/Server” and/or the “Publisher/Subscriber” messages. These data access methods are well known to those familiar with Fieldbus messaging. 
     For Client/Server and Publisher/Subscriber messages originating or terminating in the HSE Device and/or HSE Linking Device, the HSE FDA Agent  290  sends and receives the Ethernet Network  140  messages on the local interface  291 , provides the appropriate mapping to FMS services as previously described above, and uses local interfaces  293 ,  294 ,  296 ,  298 , and  299  to access the HSE NMIB  213 , HSE SMIB  212 , HSE LRE  230 , FBAP VFD(s)  260  and the HSE Management Agent  270 , respectively. HSE SMK  220  is not accessed because it has its own SM messages as previously described. 
     For Client/Server, Publisher/Subscriber and/or SM messages originating or terminating in the H 1  Network  150 , the HSE FDA Agent  290  uses local interface  297  to send and/or receive messages from H 1  Interface(s)  240 . 
     If the messages from the H 1  network  150  are to/from the Ethernet Network  140 , and are Client/Server or Publisher/Subscriber messages, HSE FDA Agent  290  uses the FMS mapping and local interface  291 . If the H 1  messages to/from the Ethernet Network  140  are SM messages, the HSE FDA Agent uses the SM mapping and local interface  292 . 
     If the messages to/from H 1  Network  150  are to/from the HSE Linking Device, and are Client/Server or Publisher/Subscriber messages, HSE FDA Agent will use FMS mapping and the appropriate local interface (except the local interfaces  291  and  292 ). 
     If the messages to/from H 1  Network  150  are to/from the HSE Linking Device, and are SM messages, HSE FDA Agent will use SM mapping and the appropriate local interface (except the local interfaces  291  and  292 ). 
     B.3: HSE System Management Kernel 
     Referring again to FIG. 2, the HSE system architecture includes a HSE System Management Kernel (SMK)  220  for each HSE device and/or each HSE linking device. The HSE SMK  220  maintains information and a level of coordination that provides an integrated network environment for the execution and interoperation of the FBAP VFD  260 . 
     As previously discussed, HSE SMK  220  provides for routine configuration of certain basic system information prior to device operation. For example HSE SMK startup takes a device through a set of predefined phases for this purpose. During this procedure a system configuration device recognizes the presence of the device on the network and configures basic information into the HSE SMIB  212 . Once the device receives its basic configuration information, its HSE SMK brings it to an operational state without affecting the operation of other devices on the network. It also enables the HSE FDA Agent  290  for use by other functions in the device. 
     B.3.1: HSE SMK System Time Synchronization 
     Now referring to FIG. 5, the HSE Management Agent  270  in HSE Linking Device  110  uses SNTP  286  to interact with remote SNTP Server  510  in Time Master  500  to synchronize System Time  501 ′ in HSE MIB  271 ′ with System Time  501  in the Time Master  500 . When System Time  501 ′ is synchronized with System Time  501 , Sync Flag (F)  510  in the HSE MIB is set to true by the standard SNTP protocol. The Time Master and the HSE Linking Device are interconnected using standard, COTS Ethernet equipment  130 . This synchronization protocol is defined in IETF RFC  2030 . 
     At any moment, Local Time  502  in HSE SMIB  212  may or may not be synchronized with System Time  501 ′. In order to coordinate execution of function blocks in a distributed system, and to provide proper time stamping of function block alarms, Local Time  502  must be Synchronized with System Time  501 ′. 
     All of the function blocks are synchronized with Start of Macrocycle, “T 0 ”  520  in HSE SMIB  212 . Each HSE Linking Device and HSE Device in the system has the same value for T 0 . A function block is executed when HSE SMK  220  locally issues a Function Block (FB) Start  221  message for the block. Each FB Start message is generated based on an offset from T 0 . 
     At the start of the macrocycle, T 0  and the offset for each block is based on Local Time  502 . Therefore each device must adjust their Local Time  502  to equal the System Time  501 ′ for the system to function properly. However, because each device has a hardware clock oscillator that is not perfect, Local Time  502  will eventually drift out of synchronization with System Time  501 ′. 
     FIG. 6 shows the process of correcting for the drift in accordance with an embodiment of the present invention. In particular, when a macrocycle ends in step  601 , the HSE SMK  220  will test the Sync Flag  510  in HSE MIB  271 ′ in step  602 . If F  510  is not true, the process ends in step  606 . 
     If, on the other hand, it is determined in step  602  above that F  510  is true, HSE SMK  220  computes the offset between Local Time  502  and System Time  501 ′ in step  603 , and sets the Local Time  502  to equal the System Time  501 ′ within a value specified in a desired time sync class (See Reference Set 1 of Appendix A herein) in step  604 . 
     Once the Local Time  502  is synchronized, in step  605 , the start time (T 0 )  520  (shown in FIG. 5) is aligned with start time of other devices. 
     The start time alignment will now be described with references to FIGS. 7A and 7B. FIG. 7A shows the macrocycle offset of a device, e.g., device N, before the time synchronization, in which the offset  720  represents the error that must be corrected in the HSE Device N. As shown, the HSE Device N now has the correct Local Time, but the start time (T 0 )  520 ′ of System Macrocycle  700 ′ is not aligned with other devices in the distributed system. 
     FIG. 7B shows the macrocycle offset of a device, e.g., device N, after the time synchronization. The HSE SMK  220  of the Device N delays the start time (T 0 )  520 ′ of the System Macrocycle  700 ′ by Offset  720  so that the System Macrocycle begins at the same time (T 0 )  520  as, e.g., System Macrocycle  700  in HSE Device  1 . HSE Device N System Macrocycle is now synchronized with the System Time, and the synchronization process ends at step  606  (shown in FIG.  6 ). 
     B.4: Local Area Network Redundancy Entity 
     Referring to FIG. 4, each HSE Device and HSE Linking Device has a HSE Local Area Network (LAN) Redundancy Entity (HSE LRE)  230 . The HSE LRE provides fault tolerance to single failure through the use of redundancy. 
     HSE LRE periodically sends and receives Redundancy Diagnostic Messages over local interface  296 . HSE FDA Agent  290  maps the Diagnostic messages on local interfaces  291  and  292  (See HSE Redundancy Specification FF-593 listed in the Reference Set 2 of Appendix A herein for the Redundancy Diagnostic Message Formats.) 
     The Redundancy Diagnostic Messages are sent concurrently on Ethernet Network  140  and Ethernet Network  140 ′. Each device receives the Redundancy Diagnostic Messages on Ethernet Network  140  and Ethernet Network  140 ′ and constructs a local Network Status Table (NST)  231 . The NST provides detailed status on the condition of every HSE device connected to Ethernet Network  140  and Ethernet Network  140 ′. The HSE LRE  230  controls which Ethernet Network  140  or  140 ′ the HSE Device will use for message transmission. 
     With this method, all of the network transmission and device switchover decisions are distributed into the HSE Devices and the system uses standard, COTS Ethernet equipment. 
     FIG. 8 illustrates the general topology supported by the redundancy aspect of the present invention. The topology shown is only an example, showing one of many possible topologies. Any topology may be used as long as behavior of the equipment providing Ethernet Networks  140  and  140 ′ is standard, COTS Ethernet equipment. 
     HSE redundancy supports both Ethernet Network redundancy and HSE Linking Device redundancy. 
     B.4.1: Ethernet Network Redundancy 
     Referring to FIG. 8, HSE Devices  120 ′ and HSE Linking Device Pairs  110 ′ have interfaces to both Ethernet Network  140  and Ethernet Network  140 ′. In this example, Ethernet Network  140  is provided by COTS Ethernet equipment  130  and Ethernet Network  140 ′ is provided by COTS Ethernet equipment  130 ′. A single failure of any one of the Ethernet Networks or one of the Ethernet interfaces on a HSE device would cause the HSE LRE previously described to force communications on the remaining functional network. 
     B.4.2: HSE Linking Device Redundancy 
     The HSE LRE  230  supports HSE Linking Device redundancy. Redundant HSE Linking Device Pair  160  comprises primary HSE Linking Device  110 , and standby HSE Linking Device  110 ′. H 1  Devices  170  are connected by H 1  Networks  150  to the Redundant HSE Linking Device Pair  160 . If primary HSE Linking Device  110  fails, standby HSE Linking Device  110 ′ will assume control. A HSE device  120 ′ may be made redundant in the same manner as the HSE linking device  110 , except in a HSE device H 1  interface(s) is (are) not present. 
     The present invention provides the necessary diagnostic message format to allow an open and interoperable switch-over of the redundant high speed Ethernet networks and/or the redundant HSE linking devices (or HSE devices). 
     The redundancy method for backup of each H 1  Network is described in the &#39;178 application, and by the specifications listed in Reference Set 1 of Appendix A herein. 
     As can be appreciated, the distributed control system architecture in the foregoing description provides an open, interoperable solution optimized for integration of distributed control systems and other control devices in a high performance backbone, provides an open, interoperable solution that provides system time synchronization suitable for distributed control applications operable over a high performance backbone, and provides an open, interoperable solution that provides a fault tolerant high performance backbone as well as fault tolerant devices that are connected to the backbone. 
     The preferred embodiments set forth above are to illustrate the invention and are not intended to limit the present invention. Additional embodiments and advantages within the scope of the claimed invention will be apparent to one of ordinary skill in the art. 
     Moreover, while the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the method of the present invention has been described by examples, the steps of the method may be performed in a different order than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope of the invention as defined in the following claims and their equivalents. 
     
       
         
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                 APPENDIX A 
               
               
                   
               
               
                 Number 
                 Revision 
                 Specification 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A.1 Reference Set 1 
               
             
          
           
               
                 FF-801 
                 FS 1.4 
                 Network Management 
               
               
                 FF-806 
                 FS 1.0 
                 Data Link Protocol - 
               
               
                   
                   
                 Bridge Operation Addendum 
               
               
                 FF-821 
                 FS 1.4 
                 Data Link Services Subset 
               
               
                 FF-822 
                 FS 1.4 
                 Data Link Protocol Subset 
               
               
                 FF-870 
                 FS 1.4 
                 Fieldbus Message Specification 
               
               
                 FF-875 
                 FS 1.4 
                 Fieldbus Access Sublayer 
               
               
                 FF-880 
                 FS 1.4 
                 System Management 
               
               
                 FF-890 
                 FS 1.4 
                 Function Block Application Process-Part 1 
               
             
          
           
               
                 A.2 Reference Set 2 
               
             
          
           
               
                 FF-803 
                 FS 1.0 
                 HSE Network Management 
               
               
                 FF-586 
                 FS 1.0 
                 HSE Ethernet Presence 
               
               
                 FF-588 
                 FS 1.0 
                 HSE Field Device Access Agent 
               
               
                 FF-589 
                 FS 1.0 
                 HSE System Management 
               
               
                 FF-593 
                 PS 2.0 
                 HSE Redundancy 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
             
           
               
                 APPENDIX B 
               
               
                   
               
               
                 RFC Number 
                 RFC Title 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 768 
                 User Datagram Protocol (UDP) 
               
               
                 791 
                 Internet Protocol (IP) 
               
               
                   
                 Amended by: 
               
               
                   
                 IP Subnet Extensions, RFC 950 
               
               
                   
                 IP Broadcast Datagrams, RFC 919 
               
               
                   
                 IP Broadcast Datagrams with Subnets, RFC 922 
               
               
                 792 
                 Internet Control Message Protocol (ICMP) 
               
               
                 793 
                 Transport Control Protocol (TCP) 
               
               
                 826 
                 Ethernet Address Resolution Protocol (ARP) 
               
               
                 894 
                 Ethernet Framing of IP Datagrams over Ethernet 
               
               
                 1042 
                 IEEE 802.2 &amp; 3 Framing of IP Datagrams over Ethernet 
               
               
                 1112 
                 Internet Group Management Protocol (IGMP) 
               
               
                 1122 
                 Requirements for Internet Hosts -- Communication 
               
               
                   
                 Layers 
               
               
                 1155 
                 Structure and Identification of Management 
               
               
                   
                 Information 
               
               
                 1157 
                 Simple Network Management Protocol (SNMP) 
               
               
                 1213 
                 Management Information Base-II (MIB II) 
               
               
                 1533 
                 DHCP Options and BOOTP Vendor Extensions 
               
               
                 1541 
                 Dynamic Host Configuration Protocol (DHCP) 
               
               
                 1643 
                 Definitions of Managed Objects for the Ethernet-like 
               
               
                   
                 Interface Types 
               
               
                 2030 
                 Simple Network Time Protocol (SNTP)