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Adaptive Shaper for Frame Relay Overview

For J-series Services Routers, you can configure adaptive shapers, which allow you to shape Frame Relay logical interfaces to a maximum rate, based on congestion. Adaptive shaping is triggered by the backward explicit congestion notification (BECN) bit in Frame Relay packet headers. Thus, adaptive shaping allows you to use the information provided in Frame Relay packet headers to detect possible congestion and to adjust your bandwidth limitation accordingly.

Adaptive shaping is triggered when the last ingress packet on the logical interface has its BECN bit set to 1. When adaptive shaping is triggered, the output queues on the logical interface are shaped according to the adaptive shaper configuration.

Adaptive shaping is an alternative to regular logical interface shaping. If the last ingress packet has its BECN bit set to 0, the logical interface queues are shaped according to the shaping-rate statement at the [edit class-of-service interfaces interface-name unit logical-unit-number] hierarchy level, which should be configured at a higher rate than the rate you configure for the adaptive shaper. If you do not include the shaping-rate statement in the configuration, the default logical interface bandwidth is the average of unused bandwidth for the number of logical interfaces that require default bandwidth treatment. For more information about the shaping-rate statement, see Associating the Scheduler Map and a Shaping Rate with a DLCI or VLAN.

To configure an adaptive shaper, you can include the following statements at the [edit class-of-service] hierarchy level of the configuration:



[edit class-of-service]

adaptive-shapers {



adaptive-shaper-name {

trigger type shaping-rate (percent percentage | rate);
}


}

interfaces {



interface-name {


unit logical-unit-number {

adaptive-shaper adaptive-shaper-name;
}


}


}

For more information, see the J-series Services Router Basic LAN and WAN Access Configuration Guide.

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