Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring Frame Relay SwitchingConfiguring Frame RelayConfiguring Frame Relay Policing ParametersTo configure policing parameters in a Frame Relay map class, use one or more of the followingcommands in map-class configuration mode:CommandRouter(config-map-class)# frame-relay cir {in | out} bpsRouter(config-map-class)# frame-relay bc {in | out} bitsRouter(config-map-class)# frame-relay be {in | out} bitsRouter(config-map-class)# frame-relay tc millisecondsPurposeSets the CIR for a Frame Relay PVC, in bits persecond.Sets the committed burst size for a Frame RelayPVC, in bits.Sets the excess burst size for a Frame Relay PVC,in bits.Sets the measurement interval for policingincoming traffic on a PVC when the CIR is zero,in milliseconds.You can associate the map class with the interface or individual switched PVCs. Switched PVCs that arenot associated with a map class will inherit policing parameters from the interface.If you use a map class to configure both traffic policing and shaping, use the in keyword to specifyincoming traffic for policing and the out keyword to specify outgoing traffic for shaping. If youconfigure shaping on one segment of a switched PVC and policing on the other, the shaping parameterswill be derived from the policing parameters unless you specifically define shaping parameters in themap class.Configuring Congestion Management on Switched PVCsFrame Relay congestion management can be used to manage outgoing traffic congestion on switchedPVCs. When Frame Relay congestion management is enabled, one way that the router managescongestion is by setting backward explicit congestion notification (BECN) and forward explicitcongestion notification (FECN) bits on packets. When a switched PVC or interface is congested, packetsexperiencing congestion are marked with the FECN bit, and packets traveling in the reverse direction aremarked with the BECN bit. When these bits reach a user device at the end of the network, the user devicecan react to the ECN bits and adjust the flow of traffic.When the output interface queue reaches or exceeds the ECN excess threshold, all Frame Relay DE bitpackets on all PVCs crossing that interface will be marked with FECN or BECN, depending on theirdirection of travel. When the queue reaches or exceeds the ECN committed threshold, all Frame Relaypackets will be marked with FECN or BECN.A second way the router manages congestion is by discarding Frame Relay packets that are marked withthe discard eligible (DE) bit and that exceed a specified level of congestion.When the queue reaches or exceeds the DE threshold, Frame Relay packets with the DE bit will bediscarded rather than queued.You can define two levels of congestion. The first level applies to individual PVCs transmitting trafficin excess of the committed information rate (CIR). The second level applies to all PVCs at an interface.This scheme allows you to adjust the congestion on PVCs transmitting above the CIR before applyingcongestion management measures to all PVCs.Congestion management parameters can be configured on the output interface queue and ontraffic-shaping queues.24