Patent Publication Number: US-6988133-B1

Title: Method and apparatus for communicating network quality of service policy information to a plurality of policy enforcement points

Description:
FIELD OF INVENTION 
   The present invention generally relates to creating and enforcing network quality of service policy information in a network. The invention relates more specifically to a method and apparatus for communicating network quality of service policy information to a plurality of policy enforcement points. 
   BACKGROUND OF THE INVENTION 
   A computer network typically comprises a plurality of interconnected entities that transmit (“source”) or receive (“sink”) data frames. A common type of computer network is a local area network (“LAN”) that generally comprises a privately owned network within a single building or campus. LANs employ a data communication protocol (LAN standard) such as Ethernet, FDDI, or Token Ring, that defines the functions performed by the data link and physical layers of a communications architecture (i.e., a protocol stack), such as the Open Systems Interconnection (OSI) Reference Model. In many instances, multiple LANs may be interconnected by point-to-point links, microwave transceivers, satellite hookups, etc., to form a wide area network (“WAN”), metropolitan area network (“ MAN”) or Intranet. These internetworks may be coupled through one or more gateways to the global, packet-switched internetwork generally known as the Internet or World Wide Web (WWW). 
   Each network entity preferably includes network communication software, which may operate in accordance with Transport Control Protocol/Internet Protocol (TCP/IP). TCP/IP generally consists of a set of rules defining how entities interact with each other. In particular, TCP/IP defines a series of communication layers, including a transport layer and a network layer. At the transport layer, TCP/IP includes both the User Data Protocol (UDP), which is a connectionless transport protocol, and TCP, which is a reliable, connection-oriented transport protocol. When a process at one network entity wishes to communicate with another entity, it formulates one or more messages and passes them to the upper layer of the TCP/IP communication stack. These messages are passed down through each layer of the stack where they are encapsulated into packets and frames. Each layer also adds information in the form of a header to the messages. The frames are then transmitted over the network links as bits. At the destination entity, the bits are re-assembled and passed up the layers of the destination entity&#39;s communication stack. At each layer, the corresponding message headers are stripped off, thereby recovering the original message that is handed to the receiving process. 
   One or more intermediate network devices are often used to couple LANs together and allow the corresponding entities to exchange information. For example, a bridge may be used to provide a “bridging” function between two or more LANs. Alternatively, a switch may be utilized to provide a “switching” function for transferring information, such as data frames or packets, among entities of a computer network. Typically, the switch is a computer having a plurality of ports that couple the switch to several LANs and to other switches. The switching function includes receiving data frames at a source port and transferring them to at least one destination port for receipt by another entity. Switches may operate at various levels of the communication stack. For example, a switch may operate at Layer  2 , which in the OSI Reference Model, is called the data link layer, and includes the Logical Link Control (LLC) and Media Access Control (MAC) sub-layers. 
   Other intermediate devices, commonly known as routers, may operate at higher communication layers, such as Layer  3 , which in TCP/IP networks corresponds to the Internet Protocol (IP) layer. Conventionally, IP data packets include a corresponding header that contains an IP source address and an IP destination address. Routers or Layer  3  switches may re-assemble or convert received data frames from one LAN standard (e.g., Ethernet) to another (e.g., Token Ring). Thus, Layer  3  devices are often used to interconnect dissimilar subnetworks. Some Layer  3  intermediate network devices may also examine the transport layer headers of received messages to identify the corresponding TCP or UDP port numbers being utilized by the corresponding network entities. Many applications are assigned specific, fixed TCP and/or UDP port numbers in accordance with Request For Comments (RFC)  1700 . For example, TCP/UDP port number  80  corresponds to the Hypertext Transport Protocol (HTTP), while port number  21  corresponds to File Transfer Protocol (FTP) service. 
   A process executing at a network entity may generate hundreds or thousands of traffic flows that are transmitted across a network. Generally, a traffic flow is a set of messages (frames and/or packets) that typically correspond to a particular task, transaction or operation (e.g., a print transaction) and may be identified by various network and transport parameters, such as source and destination IP addresses, source and destination TCP/UDP port numbers, and transport protocol. 
   The treatment that is applied to different traffic flows may vary depending on the particular traffic flow at issue. For example, an online trading application may generate stock quote messages, stock transaction messages, transaction status messages, corporate financial information messages, print messages, data backup messages, etc. A network administrator may wish to apply a different policy or service treatment (“quality of service” or “QoS”) to each traffic flow. In particular, the network administrator may want a stock quote message to be given higher priority than a print transaction. Similarly, a $1 million stock transaction message for a premium client should be assigned higher priority than a $100 stock transaction message for a standard customer. 
   Computer networks include numerous services and resources for use in moving traffic throughout the network. For example, different network links, such as Fast Ethernet, Asynchronous Transfer Mode (ATM) channels, network tunnels, satellite links, etc., offer unique speed and bandwidth capabilities. Additionally, the intermediate devices also include specific resources or services, such as number of priority queues, filter settings, availability of different queue selection strategies, congestion control algorithms, etc. 
   Individual frames or packets can be marked so that intermediate devices may treat them in a predetermined manner. For example, the Institute of Electrical and Electronics Engineers (IEEE) describes additional information for the MAC header of Data Link Layer frames in Appendix 802.1p to the 802.1D bridge standard. 
     FIG. 1A  is a partial block diagram of a Data Link frame  100  that includes a MAC destination address (DA) field  102 , a MAC source address (SA) field  104  and a data field  106 . According to the 802.1Q standard, a user — priority field  108 , among others, is inserted after the MAC SA field  104 . The user — priority field  108  may be loaded with a predetermined value (e.g., 0–7) that is associated with a particular treatment, such as background, best effort, excellent effort, etc. Network devices, upon examining the user — priority field  108  of received Data Link frames  100 , apply the corresponding treatment to the frames. For example, an intermediate device may have a plurality of transmission priority queues per port, and may assign frames to different queues of a destination port on the basis of the frame&#39;s user priority value. 
     FIG. 1B  is a partial block diagram of a Network Layer packet  120  corresponding to the Internet Protocol. Packet  120  includes a type — of −  service (ToS) field  122 , a protocol field  124 , an IP source address (SA) field  126 , an IP destination address (DA) field  128  and a data field  130 . The ToS field  122  is used to specify a particular service to be applied to the packet  120 , such as high reliability, fast delivery, accurate delivery, etc., and comprises a number of sub-fields. The sub-fields may include a 3-bit IP precedence (IPP) field and three one-bit flags that signify Delay, Throughput, and Reliability. By setting the flags, a device may indicate whether delay, throughput, or reliability is most important for the traffic associated with the packet. Thus, ToS field  122  facilitates applying various quality of service treatments to packets. 
   The Common Open Policy Service (COPS) protocol provides one approach for distributing QoS information to a network device. The COPS protocol is defined in RFC 2748, “The COPS (Common Open Policy Service) Protocol,” by J. Boyle et al., January 2000. The use of COPS for resource reservation is described in RFC 2749, “COPS usage for RSVP,” J. Boyle, et al., January 2000. The use of COPS for provisioning is described in the IETF Internet-draft document “draft-ietf-rap-cops-pr-04.txt.” Readers of this patent are assumed to have read the foregoing documents and to understand how to implement their subject matter in a working system. 
   COPS is a query and response protocol that can be used to exchange policy information between a policy server (Policy Decision Point or PDP) and its clients (Policy Enforcement Points or PEPs). One example of a policy client is a router compatible with Resource Reservation Protocol (RSVP) that must exercise policy-based admission control over RSVP usage. PEPs may be routers, switches, gateways, etc., or any other device that is configured, using one or more software elements or hardware elements, to carry out policy enforcement. 
   One drawback of the COPS protocol is that it does not provide a mechanism to enable a PDP to download configuration information to a plurality of PEPs with assurance that all the PEPs receive all the configuration information. Thus, there is no way to ensure that specified quality of service information is successfully deployed to an entire network or to a plurality of policy enforcement points. In particular, simultaneous download of configuration information to multiple devices, wherein the configuration information may differ from device to device, is not guaranteed. In one approach, a deployment is sent to and pre-tested by a plurality of target devices. Although this approach increases the likelihood of successfully installing the configuration on all the target devices, there is no guarantee of successful deployment to the entire target device group. Thus, even if such pre-testing is carried out, there is a chance that subsequent actual deployment of the QoS information will not work. For example, if network conditions change between the time of pre-testing and actual deployment, one or more devices may change one or more internal values that resulted in successful pre-testing. As a result, the later deployment may fail. 
   In yet another approach, a policy decision point could be configured to predict a response of a policy enforcement point to downloaded configuration information, if the PEP provided enough information in a COPS request (REQ) message. However, such a predictive approach has inherent limitations. In particular, a PEP could not necessarily commit to a downloaded configuration due to resource constraints, internal conflicts with other features or other types of configuration, or feature capability constraints. 
   Examples of resource constraints include insufficient memory, filters, buffers, queues, etc. Resource constraints of a PEP are extremely difficult or impossible for a PDP to predict, even if such constraints are somehow communicated to the PDP by the PEP in a request message. Internal configuration conflicts may vary from one PEP to another and change from a single device version to the following, and therefore would be too complex to predict by the PDP or communicate to the PDP in the request message. 
   If a PEP device communicates any feature capability constraints within the REQ message using PIB definitions, the PDP can predict failures caused by feature capability constraints, thereby avoiding downloading configuration information for which the PEP cannot commit. However, there is always a chance that the PEP will reject a downloaded configuration due to capability constraints, unless the configuration is previously tested by that PEP. 
   Moreover, COPS defines limited feedback reporting capabilities for PEPs. If a partial configuration is received, the PEP is required to reject it and report rejection to the sending PDP. However, there is no way for the PEP to report to a PDP that one or more constraints of the PEP are preventing or will prevent proper implementation of a configuration by the PEP. 
   The consequences of these drawbacks can be severe. If a provisioned device configuration is downloaded to less than all intended devices, or if a partial download of a configuration occurs with respect to a single network device, unpredictable results may occur. At best a minor system malfunction may occur, or a major system failure may occur in a worst case. For example, a partial download of a Differentiated Services configuration may result in inconsistent application of QoS per hop behavior over the network. As another example, sending partial virtual private network configuration information to devices that are intended to form a VPN may result in malfunctioning of the virtual private network. As a third example, a deploying a partial security configuration may result in creating one or more server security holes, or denial of services to innocent users (“insults”). 
   Based on the foregoing, there is a clear need for a way to deploy quality of service policy information to a plurality of network devices, or to an entire network, with assurance that all devices will receive all applicable policy information. 
   There is a specific need for a way to adapt the COPS protocol to operate in transactions with multiple policy enforcement points. 
   SUMMARY OF THE INVENTION 
   The foregoing needs, and other needs and objects that will become apparent for the following description, are achieved in the present invention, which comprises, in one aspect, a method for communicating network quality of service policy information to a plurality of policy enforcement points. Active QoS configuration information is created and stored at a policy enforcement point, such as a router in a network. New configuration information is received and stored as an inactive configuration of the policy enforcement point. The policy enforcement point determines whether the inactive configuration information is properly functional in combination with the active QoS configuration information. The new configuration information is made active in place of the active QoS configuration information only in response to receiving an activation message. 
   According to one feature, receiving new configuration information comprises receiving a COPS protocol decision message from the policy decision point that identifies the configuration information as an inactive configuration by a specified flag bit in a message type value in a Context object that forms part of the decision message. 
   Using the method, network quality of service policy information may be communicated to a plurality of policy enforcement points, with assurance that all receiving policy enforcement points can successfully deploy the configuration information. The new configuration information is received and stored in an inactive configuration area of memory of the policy enforcement point. The inactive configuration is actively deployed only after it is tested in combination with existing active configuration information, and its operability is validated through various checks and tests. An inactive configuration is signaled by a specified COPS protocol message, and other COPS messages are defined to provide for deploying or activating the inactive configuration. As a result, new QoS policy configuration information can be deployed to an entire network or to a large plurality of devices with assurance that all such information is received and deployed without adverse effects on the network or enforcement of policy information. 
   In other aspects, the invention encompasses a computer apparatus, a computer readable medium, and a carrier wave configured to carry out the foregoing steps. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
       FIG. 1A  is a prior art partial block diagram of a network message. 
       FIG. 1B  is a prior art partial block diagram of a network message. 
       FIG. 2  is a block diagram of a computer network in which in which the present invention may be utilized. 
       FIG. 3A  is a block diagram of a PDP and a PEP illustrating use of COPS. 
       FIG. 3B  is a block diagram of a policy enforcement point that can participate in multiple-device policy deployment transactions. 
       FIG. 4A  is a flow diagram of a portion of one process of installing inactive QoS configuration information. 
       FIG. 4B  is a flow diagram of another portion of a process of installing inactive QoS configuration information. 
       FIG. 4C  is a flow diagram of an alternative process of installing inactive QoS configuration information. 
       FIG. 5  is a block diagram that illustrates a computer system upon which an embodiment may be implemented. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A method and apparatus for communicating network quality of service policy information to a plurality of policy enforcement points is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
   Operational Context 
     FIG. 2  is a block diagram of a computer network  200  illustrating certain elements of an embodiment. Generally, computer network  200  includes one or more network devices  220 ,  222 ,  224 ,  226  a plurality of workstations  216 ,  218 , a policy management station  202  and a network  228 . 
   Network devices  220 ,  222  represent edge network devices such as routers, switches, or other similar or equivalent devices that are configured for coloring packets within network  228 . In one embodiment, network devices  220 ,  222  are configured to execute the Cisco Internetworking Operating System (IOS) and are capable of marking packets with DSCP values, i.e., they are compatible with Differentiated Services. Such marking may be carried out using a marker or other software element or application that runs under control of IOS, e.g., an agent or process. Network devices  224 ,  226  represent internal network devices such as routers, switches, or other similar or equivalent devices that are configured for forwarding packets within network  228  based the color of each packet. In certain embodiments, network devices  224 ,  226  are configured to execute the Cisco Internetworking Operating System (IOS) and are capable of forwarding packets based on their DSCP values, i.e., they are compatible with Differentiated Services. It should be noted that network devices  220 ,  222  and network devices  224 ,  226  may in fact represent similar or even identical device types and/or models that are each configured to perform a designated function within computer network  200 . 
   Workstations  216 ,  218  may be personal computers, workstations, or other network end stations at which work is done, such as printers, scanners, facsimile machines, etc. In certain embodiments, workstations  216 ,  218  may themselves be network devices, such as bridges, gateways, routers or switches that allow computer network  200  to connect to another network system. For example, workstation  216  may be an edge device that is configured for coloring packet of a different DS domain. In certain embodiments, workstations  216 ,  218  execute one or more applications  212 ,  214 . Applications  212 ,  214  may represent a variety of different computer applications that execute on workstations  216 ,  218  respectively and which cause data to be sent and received over network  228 . 
   Network  228  is a network system comprising any number of network devices. Network  228  may form part of a LAN or WAN. In one embodiment, network  228  is a packet-switched IP network configured as a DS domain whereby treatment of packets that flow through network  228  is controlled and managed by Policy Management Station  202  and network devices  220 ,  222 ,  224 ,  226 . 
   Policy Management Station  202  is a computer, or a group of hardware or software components or processes that cooperate or execute in one or more computer systems. In this example, Policy Management Station  202  includes a policy coordinator  204  and one or more policy servers  206 ,  208 ,  210 , which are coupled to network devices  220 ,  222 ,  224 ,  226 . In one embodiment, policy coordinator  204  communicates with policy servers  206 ,  208 ,  210  to configure the network devices  220 ,  222 ,  224 ,  226 , to control the coloring and forwarding of packets within network  228 . For example, policy coordinator  204  may direct network devices  220 ,  222  to color the packets of all Voice Over IP (VOIP) flows as Gold (high priority) and to color the packets of all File Transfer Protocol (FTP) flows as Bronze (low priority). Each color corresponds to a particular service level and is associated with one or more QoS treatment parameters, e.g., a pre-defined DSCP value and possibly other values or characteristics. Policy coordinator  204  may further direct network devices  224 ,  226  to apply a particular forwarding policy based on the particular color of each packet that is processed. 
   In one embodiment, Policy Management Station  202  provides a mechanism whereby a network administrator may select or define a desired service level that is to be applied to a particular group of data flows within network  228 . For example, an administrator may choose to have a service level of Gold be applied to all VOIP flows within computer network  200 . In response, policy coordinator  204  communicates with the policy servers to cause edge devices  220 ,  222  to set an initial DiffServ Codepoint value in the packets of all VOIP flows. An example of a commercial product suitable for use as Policy Management Station  202  is CiscoAssure QoS Policy Manager 1.0, commercially available from Cisco Systems, Inc. 
   In certain embodiments, policy coordinator  204  includes a service monitor  230  that consists of one or more hardware or software elements that are configured to collect dropped packet information based on the number of packets that are dropped by network devices  220 ,  222 ,  224 ,  226  within network  228 . Based on the dropped packet information, service monitor  230  determines whether a particular service level is receiving the required level of service. If service monitor  230  determines that a particular service level is not receiving the required level of service (e.g., packets belonging to that service level are being dropped), service monitor  230  determines an updated QoS treatment policy for achieving the required service level for the associated group of data flows. Service monitor  230  then communicates the updated QoS treatment policy to markers or other elements of devices  220 ,  222  to dynamically color the packets of each flow to better meet the specific bandwidth needs of the data flows. Examples of how dropped packet information may be determined is described in detail below. 
   Although the example embodiment of  FIG. 2  shows two (2) workstations  216 ,  218 , three (3) policy servers  216 ,  208 ,  210 , two (2) edge devices  220 ,  222 , and two (2) core devices  224 ,  226 , in other practical embodiments there may be any number of such elements. In addition, Policy Management Station  202  is provided as only an example of one type configuration that may be used to manage QoS policies. Thus, Policy Management Station  202  may be configured as a single component or instead variety of different distributed components that are configured for implementing adaptive QoS policies to maintain the level of service that is required by the service levels within a network. In addition, although not depicted in  FIG. 2 , in certain embodiments, policy servers  206  and  210  are coupled to network  228  and thus may communicate with edge devices  220  and  222  over network  228 . 
     FIG. 3A  is a block diagram of a policy decision point and a policy enforcement point in a network that illustrates use of COPS. 
   A policy decision point  302  is coupled by link  306 , which sends and receives COPS messages, to policy enforcement point  304 . One or more transmission paths  308 A,  308 B are coupled to PEP  304 , and typically terminate in a network element of a LAN, WAN, Internet, etc. In this way, policy decision point  302  can execute one or more QoS policy decisions and efficiently communicate the decisions to PEP  304 , which enforces the decisions with respect to network traffic traveling through PEP  304  on paths  308 A,  308 B. An optional Local Policy Decision Point (LPDP) can be used by PEP  304  to make local policy decisions in the absence of a PDP. The PEP may communicate with a policy server (herein referred to as a remote PDP) to obtain policy decisions or directives. 
   Each PEP initiates a persistent TCP connection to a PDP and uses the TCP connection to send requests to and receive decisions from the remote PDP. One PDP implementation per server listens on a well-known TCP port number, e.g., port  3288 . The PEP is responsible for initiating the TCP connection to a PDP. 
   Communication between the PEP and remote PDP generally comprises a request to which a decision is provided a response, however, the remote PDP may send unsolicited decisions to the PEP to force changes in previously approved request states. The PEP also can report to the remote PDP that it has successfully completed performing a decision of a PDP decision locally, which is useful for accounting and monitoring purposes. The PEP is responsible for notifying the PDP when a request state has changed on the PEP. Further, the PEP is responsible for the deletion of any state that is no longer applicable due to events at the client or decisions issued by the server. 
   Under COPS, when a PEP sends a configuration request, the PDP continuously sends named units of configuration data to the PEP via decision messages as applicable for the configuration request. When a unit of named configuration data is successfully installed on the PEP, the PEP sends a report message to the PDP confirming the installation. The server may then update or remove the named configuration information via a new decision message. When the PDP sends a decision to remove named configuration data from the PEP, the PEP will delete the specified configuration and send a report message to the PDP as confirmation. 
   COPS communicates self-identifying objects that contain data necessary for identifying request states, establishing the context for a request, identifying the type of request, referencing previously installed requests, relaying policy decisions, reporting errors, providing message integrity, and transferring client specific/namespace information. 
   The context of each request corresponds to the type of event that triggered it. A COPS Context object identifies the type of request and message (if applicable) that triggered a policy event via its message type and request type fields. The Context object is defined in detail in RFC 2748, section 2.2.2. COPS identifies three types of outsourcing events: (1) the arrival of an incoming message (2) allocation of local resources, and (3) the forwarding of an outgoing message. Each of these events may require different decisions to be made. The content of a COPS request/decision message depends on the context. A fourth type of request is useful for types of clients that wish to receive configuration information from the PDP. This allows a PEP to issue a configuration request for a specific named device or module that requires configuration information to be installed. 
     FIG. 3B  is a simplified block diagram of a policy enforcement point that can participate in multiple-device policy deployment transactions. 
   In general, PEP  304  has memory  352 , COPS Agent  358 , and IOS  360 . PEP  304  may have other elements that are useful to carry out policy enforcement functions but that are not essential to the invention. For example, PEP  304  may have one or more network interfaces, processors, switching circuitry, a terminal interface, etc. In one embodiment, PEP  304  is a router that is configured to carry out the functions set forth herein. 
   Memory  352  comprises an Active Configuration  354  and an Inactive Configuration  356 . Active Configuration  354  comprises a plurality of configuration parameter values stored min association with one another, and represents the then-current configuration of PEP  304 . The Active Configuration  354  determines the operational behavior of the device. Similarly, Inactive Configuration  356  comprises a plurality of configuration parameter values, but is inactive and does not affect operation of PEP  304  or its participation in QoS policy enforcement. Active Configuration  354  and Inactive Configuration  356  each are formatted as a Policy Information Base (PIB). 
   IOS  360  is an operating system software element that controls and supervises basic functions of PEP  304 . In one embodiment, IOS  360  is the Internetworking Operating System of Cisco Systems, Inc. 
   COPS Agent  358  is an application software element that enables PEP  304  and IOS  360  to communicate over appropriate interfaces using the COPS protocol. In one embodiment, COPS Agent  358  is one or more software elements that interact with IOS  360  in order to carry out COPS functions including the specific functions described herein. In one embodiment, COPS Agent  358  includes an Inactive Configuration Module  359  that comprises one or more sequences of program instructions for carrying out the specific functions described herein. Thus, the invention disclosed herein may be implemented in one or more software elements that are executed by a network device, for example, by modifying existing COPS processing software of a network device to carry out the functions described herein. 
   “Install But Not Deploy” Process 
   According to one embodiment, a process of installing QoS configuration information in a network device without deploying the information is provided. In certain descriptions herein, the process is termed “install but not deploy” or “inactive installation.” 
   Generally, initially, an Inactive Configuration is made equal to an Active Configuration. In an alternative embodiment, storing inactive configuration information involves storing one or more PIB variable values that are marked as inactive. In this embodiment, the Inactive Configuration may comprise a subset of the Active Configuration, whereas the Active Configuration contains at least one value for all defined PIB variables. Upon startup or otherwise at initialization of a PEP, the Active Configuration is the same as the Inactive Configuration, and one or both change only in response to the PEP receiving decision information from a PDP. 
   Each PEP maintains active and inactive configuration information in a similar way. In one embodiment, a PDP makes a policy decision and sends corresponding policy decision information, with decision context information, to one or more PEP devices. Each PEP device determines, based on the decision context information, which configuration (active or inactive) should receive the policy decision information. 
   The PEP then performs one or more consistency and applicability checks, and based on the results, determines whether to install the decision information. If the PEP accepts the decision information, then the PEP stores the decision information in either the Active Configuration or the Inactive Configuration, and issues a commit report. If the PEP decides not to install the decision, then the PEP sends a reject message to the originating PDP, and issues a non-commit report. 
     FIG. 4A  and  FIG. 4B  are flow diagrams of examples of one inactive installation process, and  FIG. 4C  is a flow diagram of an alternative inactive installation process. Inactive Configuration Module  359  of COPS Agent  358  may be implemented using one or more sequences of computer program instructions that carry out the processes of  FIG. 4A ,  FIG. 4B , or  FIG. 4C . 
   Referring first to  FIG. 4A , a process is provided in which a policy decision point may install or delete one or more policy information base (PIB) items as an inactive configuration at a policy enforcement point. In block  402 , one or more policy information base values are received. Block  402  may involve receiving, at a policy enforcement point, a request to install an inactive (“background”) configuration, receiving one or more PIB variable values and storing them as part of inactive configuration information, e.g., Inactive Configuration  356  of PEP  304  of  FIG. 3B . 
   In one specific embodiment, installation of an inactive configuration is signaled in a COPS protocol message. The COPS protocol defines an Install Context object that is used for regular install/delete decision (“DEC”) messages, as described in RFC 4748, section 4.2.2. The Context object comprises a 4-byte Request Type (“R-type”) value and a Message Type (“M-type”) value, which is also 16 bits in length. The M-type carries a plurality of client-specific flag values. Thus, installation of an Inactive Configuration may be signaled by a specified M-type value in the Context object. For example, the M-type value “0×01” may signify a request to install an Inactive Configuration. The specified M-Type value, together with an Install Context flag, is sent by a PDP in a DEC message when installing Inactive configuration information. Further, when a PEP responds with a reply (“REP”) mes sage, the specified M-Type value is placed in the REP message. 
   Referring now to  FIG. 4C , in one embodiment, as shown by block  403 , a policy enforcement point determines that the policy information base values that it received in block  402  are part of an inactive configuration based on a flag bit in the message type value of the Context object of a COPS DEC message. 
   Referring again to  FIG. 4A , in block  404 , the policy enforcement point stores the policy information base values as part of an inactive configuration. In one embodiment, the values are stored in Inactive Configuration  356  under control of instructions in Inactive Configuration Module  359 . 
   In block  406 , the PEP tests the inactive installation as if it is deployed on top of the active configuration, i.e., in combination with the then-current active configuration. Such testing may involve, for example, carrying out consistency checks, verifying that all needed resources are available, etc., with respect to the resulting modified configuration. Consistency checks may involve checking consistency of the values in the resulting configuration. Thus, the PEP may determine whether the new configuration information will work if deployed, without actively deploying it until such determination is complete. 
   If such testing is unsuccessful, as indicated by block  408  and block  412 , an error is reported to the policy decision point. 
   Otherwise, control passes to the steps of  FIG. 4B . The policy enforcement point retains in memory both its active configuration information and the newly installed, inactive configuration information. 
   In block  420 , the policy enforcement point tests whether a Delete Background (Inactive) COPS message is received. The format of this message is the same as the conventional COPS PR DEC message with the exception that the Flag value in the “Decision Flag” COPS Object includes the new inactive flag. The BNF format of this message is:
         &lt;Decision Message&gt;::=&lt;Common Header&gt;
           &lt;Client Handle&gt;   [&lt;Decision&gt;]+|&lt;Error&gt;   [&lt;Integrity&gt;]
 
Where:
   
               &lt;Decision&gt;::=&lt;Context&gt;   &lt;Decision: Command-Code&gt;//i.e. decision flag object which includes the inactive flag.   [&lt;Decision: Named Data&gt;]   and, &lt;Decision: Named Data&gt;::=&lt;&lt;Install Decision&gt;|&lt;Remove Decision&gt;&gt;   

   If the test of block  420  is true, then the Active Configuration  354  is not changed, however, the PEP deletes all values from the Inactive Configuration  356 , as indicated by block  422 . In one embodiment, the Inactive Configuration  356  is then automatically updated by copying values from the Active Configuration  354 , so that both sets of information are the same. 
   In block  424 , the policy enforcement point tests whether a regular empty install decision (DEC) message has arrived from the PDP. A DEC message is termed “empty” when it does not carry the name of a particular configuration object that contains configuration information. Such a message instructs the policy enforcement point to deploy the inactive configuration information, i.e., make the inactive configuration information active. In response, the PEP updates Active Configuration  354  with information from Inactive Configuration  356 , as indicated by block  426 , and begins using it for enforcement of quality of service. Such updating involves introducing one or more new configuration parameters into Active Configuration  356  and may also involve updating existing parameters of the Active Configuration based on the Inactive Configuration. In other words, block  426  does not imply merely copying the Inactive Configuration to the Active Configuration. 
   Because such updating may involve modifying the Active Configuration, in one embodiment, PEP also sets Inactive Configuration  356  equal to Active Configuration  354 , as indicated by block  428  after carrying out the update. This ensures that after the update, the Inactive Configuration  356  is identical to the Active Configuration  354  until new inactive configuration information is received. Making Inactive Configuration  356  equal to Active Configuration  354  may involve first deleting all values from the Inactive Configuration. 
   In block  430 , the policy enforcement point tests whether a non-empty install DEC message has arrived. Such a message carries the name of a configuration object that contains configuration information, and instructs the PEP to activate the named configuration  4  information and disregard any previous inactive installation information. 
   In response, in block  432  the PEP installs the named object as the active configuration. Further, in block  434  the PEP removes the inactive information from memory, and resets the inactive configuration to be equal to the named configuration information, as indicated by block  436 . Thus, a non-empty install decision message will install a named configuration and also eliminate an inactive configuration that was associated with the prior active configuration that has been replaced by the named configuration. 
   The steps of block  428  and block  436  also may involve issuing one or more responsive messages from the PEP to the PDP. For example, the PEP can issue a commit report to the PDP that indicates that the PEP successfully committed the inactive configuration. In this context, to “commit” means to deploy or make active for use in pol icy enforcement by the PEP. 
   Accordingly, a simple and effective method for communicating network quality of service policy information to a plurality of policy enforcement points, with assurance that all receiving policy enforcement points can successfully deploy the configuration information, has been described. Using the approach described herein, new configuration information is actively deployed only after it is tested in combination with existing configuration information, and operability is validated through various checks and tests. As a result, new QoS policy configuration information can be deployed to an entire network or to a large plurality of devices with assurance that all such information is received and deployed without adverse effects on the network or enforcement of policy information. 
   In this embodiment, the PEP may accept a plurality of “inactive” installations that build a complete inactive configuration in incremental steps. Support for inactive installation may be optional, such that a PEP that does not recognize inactive installation may reject the inactive install DEC message. 
   It will be apparent that each PDP decision that is sent to a PEP is identified as relating to either the Active Configuration or Inactive Configuration. Preferably, the PDP never sends messages in which the applicable configuration is ambiguous or undefined. Also preferably, the first decision that the PDP sends after receiving a new request is an active configuration decision. 
   According to the rules of operation described herein, any decision about the Active Configuration results in a reset of the Inactive Configuration. In one specific embodiment, each PDP resets its Inactive Configuration, without changing its Active Configuration information, in response to receiving a null active configuration decision. Thus, the null active configuration decision provides a mechanism for resetting the Inactive Configuration without requiring a change to the Active Configuration. 
   The foregoing process is compatible with all PEPs, including those that do not include software elements or other means to respond to the messages defined herein. In particular, assume that a PEP does not support use of Inactive Configuration information, but receives a DEC message with the specified M-Type flag value in the Context object. In response, the device will return an Error object indicating that the device does not support the requested action. In one embodiment, a new General Error value is defined to indicate “Active configuration support only.” Definition of such a new error value enables a PDP or other application to determine exactly why a PEP has rejected a DEC message containing the specified M-type flag value in the Context object. 
   Hardware Overview 
     FIG. 5  is a block diagram that illustrates a computer system  500  upon which an embodiment of the invention may be implemented. The preferred embodiment is implemented using one or more computer programs running on a network element such as a router device. Thus, in this embodiment, the computer system  500  is a router. 
   Computer system  500  includes a bus  502  or other communication mechanism for communicating information, and a processor  504  coupled with bus  502  for processing information. Computer system  500  also includes a main memory  506 , such as a random access memory (RAM), flash memory, or other dynamic storage device, coupled to bus  502  for storing information and instructions to be executed by processor  504 . Main memory  506  also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor  504 . Computer system  500  further includes a read only memory (ROM)  508  or other static storage device coupled to bus  502  for storing static information and instructions for processor  504 . A storage device  510 , such as a magnetic disk, flash memory or optical disk, is provided and coupled to bus  502  for storing information and instructions. 
   An communication interface  518  may be coupled to bus  502  for communicating information and command selections to processor  504 . Interface  518  is a conventional serial interface such as an RS-232 or RS-422 interface. An external terminal  512  or other computer system connects to the computer system  500  and provides commands to it using the interface  514 . Firmware or software running in the computer system  500  provides a terminal interface or character-based command interface so that external commands can be given to the computer system. 
   A switching system  516  is coupled to bus  502  and has an input interface  514  and an output interface  519  to one or more external network elements. The external network elements may include a local network  522  coupled to one or more hosts  524 , or a global network such as Internet  528  having one or more servers  530 . The switching system  516  switches information traffic arriving on input interface  514  to output interface  519  according to pre-determined protocols and conventions that are well known. For example, switching system  516 , in cooperation with processor  504 , can determine a destination of a packet of data arriving on input interface  514  and send it to the correct destination using output interface  519 . The destinations may include host  524 , server  530 , other end stations, or other routing and switching devices in local network  522  or Internet  528 . 
   The invention is related to the use of computer system  500  for communicating network quality of service policy information to a plurality of policy enforcement points. According to one embodiment of the invention, communicating network quality of service policy information to a plurality of policy enforcement points is provided by computer system  500  in response to processor  504  executing one or more sequences of one or more instructions contained in main memory  506 . Such instructions may be read into main memory  506  from another computer-readable medium, such as storage device  510 . Execution of the sequences of instructions contained in main memory  506  causes processor  504  to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory  506 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. 
   The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor  504  for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device  510 . Volatile media includes dynamic memory, such as main memory  506 . Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus  502 . Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. 
   Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. 
   Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor  504  for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system  500  can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus  502  can receive the data carried in the infrared signal and place the data on bus  502 . Bus  502  carries the data to main memory  506 , from which processor  504  retrieves and executes the instructions. The instructions received by main memory  506  may optionally be stored on storage device  510  either before or after execution by processor  504 . 
   Communication interface  518  also provides a two-way data communication coupling to a network link  520  that is connected to a local network  522 . For example, communication interface  518  may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface  518  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface  518  sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. 
   Network link  520  typically provides data communication through one or more networks to other data devices. For example, network link  520  may provide a connection  4  through local network  522  to a host computer  524  or to data equipment operated by an Internet Service Provider (ISP)  526 . ISP  526  in turn provides data communication services through the world wide packet data communication network now commonly referred to as the “Internet”  528 . Local network  522  and Internet  528  both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link  520  and through communication interface  518 , which carry the digital data to and from computer system  500 , are exemplary forms of carrier waves transporting the information. 
   Computer system  500  can send messages and receive data, including program code, through the network(s), network link  520  and communication interface  518 . In the Internet example, a server  530  might transmit a requested code for an application program through Internet  528 , ISP  526 , local network  522  and communication interface  518 . In accordance with the invention, one such downloaded application provides for communicating network quality of service policy information to a plurality of policy enforcement points. 
   The received code may be executed by processor  504  as it is received, and/or stored in storage device  510 , or other non-volatile storage for later execution. In this manner, computer system  500  may obtain application code in the form of a carrier wave. 
   Alternatives And Variations 
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.