4. Alternatively, configure the committed rate and committed burst size in bytes.QOS-POLICY-OUT modeDell(config-qos-policy-out)# rate shape Kbps peak-rate burst-KB committedKbps committed-rate burst-KBConfiguring Weights and ECN for WREDThe WRED congestion avoidance functionality drops packets to prevent buffering resources from beingconsumed. Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrivemight be greater than others. In this case, the space on the buffer and traffic manager (BTM) (ingress oregress) can be consumed by only one or few types of traffic, leaving no space for other types. You canapply a WRED profile to a policy-map so that the specified traffic can be prevented from consuming toomuch of the BTM resources.WRED drops packets when the average queue length exceeds the configured threshold value to signifycongestion. ECN is a capability that enhances WRED by marking the packets instead of causing WRED todrop them when the threshold value is exceeded. If you configure ECN for WRED, devices employ ECNto mark the packets and reduce the rate of sending packets in a congested network.In a best-effort network topology, data packets are transmitted in a manner in which latency orthroughput is not maintained to be at an effective level. Packets are dropped when the networkexperiences a large traffic load. This best-effort network deployment is not suitable for applications thatare time-sensitive, such as video on demand (VoD) or voice over IP (VoIP) applications. In such cases, youcan use ECN in conjunction with WRED to resolve the dropping of packets under congested conditions.Using ECN, the packets are marked for transmission at a later time after the network recovers from theheavy traffic state to an optimal load. In this manner, enhanced performance and throughput areachieved. Also, the devices can respond to congestion before a queue overflows and packets aredropped, enabling improved queue management.When a packet reaches the device with ECN enabled for WRED, the average queue size is computed. Tomeasure the average queue size, a weight factor is used. This weight factor is user-configurable. You canuse the wred weight number command to configure the weight for the WRED average queue size. Themark probability value is the number of packets dropped when the average queue size reaches themaximum threshold value.The weight factor is set to zero by default, which causes the same behavior as dropping of packets byWRED during network loads or also called instantaneous ECN marking. In a topology in which congestionof the network varies over time, you can specify a weight to enable a smooth, seamless averaging ofpackets to handle the sudden overload of packets based on the previous time sampling performed. Youcan specify the weight parameter for front-end and backplane ports separately in the range of 0 through15.You can enable WRED and ECN capabilities per queue for granularity. You can disable these functionalityper queue, and you can also specify the minimum and maximum buffer thresholds for each color-codingof the packets. You can configure maximum drop rate percentage of yellow and green profiles. You canset up these parameters for both front-end and backplane ports.Quality of Service (QoS) 731
