870 | Quality of Servicew w w . d e l l . c o m | s u p p o r t . d e l l . c o mStrict-priority QueueingYou can assign strict-priority to one unicast queue, 1-7, using the command strict-priority fromCONFIGURATION mode. Strict-priority means that FTOS dequeues all packets from the assigned queuebefore servicing any other queues.• The strict-priority supersedes bandwidth-percentage an bandwidth-weight percentage configurations.• A queue with strict-priority can starve other queues in the same port-pipe.• On the E-Series, this configuration is applied to the queue on both ingress and egress.Weighted Random Early DetectionWeighted Random Early Detection is supported only on platform eWeighted Random Early Detection (WRED) congestion avoidance mechanism that drops packets toprevent buffering 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. A WRED profile can be applied to a policy-map sothat specified traffic can be prevented from consuming too much of the BTM resources.WRED uses a profile to specify minimum and maximum threshold values. The minimum threshold is theallotted buffer space for specified traffic, for example 1000KB on egress. If the 1000KB is consumed,packets will be dropped randomly at an exponential rate until the maximum threshold is reached(Figure 41-13); this is the “early detection” part of WRED. If the maximum threshold—2000KB, forexample—is reached, then all incoming packets are dropped until less than 2000KB of buffer space isconsumed by the specified traffic.Figure 41-13. Packet Drop Rate for WREDlMin Max0KBBuffer SpacePacket Drop Rate0 PcktsAll PcktsTotal Buffer SpaceAllotted SpaceEarly WarningNo Packets BufferedfnC0045mp
