Adaptive Frame Relay Traffic Shaping for Interface Congestion
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Adaptive Frame Relay Traffic Shaping for Interface CongestionLast Updated: October 6, 2011
Finding Feature InformationYour software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Feature OverviewThe Adaptive Frame Relay Traffic Shaping for Interface Congestion feature enhances Frame Relay traffic shaping functionality by adjusting permanent virtual circuit (PVC) sending rates based on interface congestion. When this new feature is enabled, the traffic-shaping mechanism monitors interface congestion. When the congestion level exceeds a configured value called queue depth , the sending rate of all PVCs is reduced to the minimum committed information rate (minCIR). As soon as interface congestion drops below the queue depth, the traffic-shaping mechanism changes the sending rate of the PVCs back to the committed information rate (CIR). This process guarantees the minCIR for PVCs when there is interface congestion.
This new feature works in conjunction with backward explicit congestion notification (BECN) and Foresight functionality. If interface congestion exceeds the queue depth when adaptive shaping for interface congestion is enabled along with BECN or ForeSight, then the PVC sending rate is reduced to the minCIR. When interface congestion drops below the queue depth, then the sending rate is adjusted in response to BECN or ForeSight. Before the introduction of this feature, interface congestion caused packets to be delayed or dropped at the interface. The Adaptive Frame Relay Traffic Shaping for Interface Congestion feature helps ensure that packet drop occurs at the virtual circuit (VC) queues. When used with FRF.12 fragmentation, this feature also ensures that packets are dropped before fragmentation occurs. BenefitsThe Adaptive Frame Relay Traffic Shaping for Interface Congestion feature:
Supported Platforms
Platform Support Through Feature NavigatorCisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Feature Navigator. Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature. Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. To access Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Feature Navigator is updated when major Cisco IOS software releases and technology releases occur. As of May 2001, Feature Navigator supports M, T, E, S, and ST releases. You can access Feature Navigator at the following URL: http://www.cisco.com/go/fn Supported Standards and MIBs and RFCsPrerequisitesIn order to use the Adaptive Frame Relay Traffic Shaping for Interface Congestion feature, Frame Relay traffic shaping must be enabled on the interface. Configuration TasksConfiguring Frame Relay Adaptive Traffic ShapingTo configure a map class for adaptive traffic shaping for interface congestion, use the following commands beginning in global configuration mode: DETAILED STEPS
Verifying Frame Relay Adaptive Traffic ShapingSUMMARY STEPS
DETAILED STEPS Configuration ExamplesExample Frame Relay Adaptive Traffic Shaping for Interface Congestion In the following example, the rate of traffic destined for PVC
200 will be reduced to the minCIR if the number of packets in the interface
queue exceeds 10. When the number of packets in the interface queue drops below
10, then the traffic rate will immediately return to the CIR.
interface serial0 encapsulation frame-relay frame-relay traffic-shaping frame-relay interface-dlci 200 class adjust_vc_class_rate ! map-class frame-relay adjust_vc_class_rate frame-relay cir 64000 frame-relay mincir 32000 frame-relay adaptive-shaping interface-congestion 10 GlossaryBECN --backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate. CIR --committed information rate. The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated traffic metrics. ForeSight --A network traffic control feature used in Cisco switches. When the ForeSight feature is enabled on the switch, the switch will periodically send out a ForeSight message. When a Cisco router receives a ForeSight message indicating that certain data-link connection identifiers (DLCIs) are experiencing congestion, the router reacts by activating its traffic-shaping function to slow down the output rate. FRF.12 --An implementation agreement developed to allow long data frames to be fragmented into smaller pieces and interleaved with real-time frames. In this way, real-time voice and nonreal-time data frames can be carried together on lower-speed links without causing excessive delay to the real-time traffic. minCIR --The minimum acceptable incoming or outgoing committed information rate (CIR) for a Frame Relay virtual circuit. PVC --permanent virtual circuit or connection. A virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and teardown in situations where certain virtual circuits must exist all the time. SVC --switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic. Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R) Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. © 2011 Cisco Systems, Inc. All rights reserved.
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