Quality of Service (QoS) | 431Strict-Priority QueueingTo assign strict-priority to one unicast queue, 1 to 3, use the strict-priority command fromCONFIGURATION mode. Strict-priority means that FTOS dequeues all packets from the assigned queuebefore servicing any other queues.• The strict-priority command supersedes the bandwidth-percentage command percentage configurations.• A queue with strict-priority can starve other queues in the same port-pipe.• If more than two strict priority queues are configured, the strict priority queue with a higher queuenumber is scheduled first.Weighted Random Early DetectionThe weighted random early detection (WRED) congestion avoidance mechanism drops packets to preventbuffering resources from being consumed.Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might begreater than others. In this case, the space on the BTM (ingress or egress) can be consumed by only one ora few types of traffic, leaving no space for other types. You can apply a WRED profile to a policy-map sothat you can prevent specified traffic from consuming too much of the BTM resources.WRED uses a profile to specify the minimum and maximum threshold values. The minimum threshold isthe allotted buffer space for specified traffic, for example 1000KB on egress. If the 1000KB is consumed,packets are dropped randomly at an exponential rate until the maximum threshold is reached(Figure 24-11); this is the early detection part of WRED. If the maximum threshold—2000KB, forexample—is reached, all incoming packets are dropped until less than 2000KB of buffer space isconsumed by the specified traffic.Figure 24-11. Packet Drop Rate for WREDlYou can create a custom WRED profile or use on of the five pre-defined profiles.Min Max0KBBuffer SpacePacket Drop Rate0 PcktsAll PcktsTotal Buffer SpaceAllotted SpaceEarly WarningNo Packets BufferedfnC0045mp
