Dell Force10 S4820T S4820T Configuration Guide - Page 776

www.dell.com | support.dell.com QoS Rate Adjustment is disabled by default, and no qos-rate-adjust is listed in the running-configuration. Task Command Syntax Include a specified number of bytes of packet overhead to include in rate limiting, policing, and shaping calculations. For example, to include the Preamble and SFD, enter qos-rate-adjust 8. For variable length overhead fields you must know the number of bytes you want to include. qos-rate-adjust overhead-bytes Default: Disabled C-Series and S-Series Range: 1-31 E-Series Range: 1-144 Command Mode CONFIGURATION Strict-priority Queueing You can assign strict-priority to one unicast queue, 1-7, using the command strict-priority from CONFIGURATION mode. Strict-priority means that FTOS dequeues all packets from the assigned queue before 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 Detection Weighted Random Early Detection is supported only on platform e S4820T Weighted Random Early Detection (WRED) congestion avoidance mechanism that drops packets to prevent buffering resources from being consumed. Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be greater than others. In this case, the space on the BTM (ingress or egress) can be consumed by only one or a few types of traffic, leaving no space for other types. A WRED profile can be applied to a policy-map so that 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 the allotted 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 38-13); this is the "early detection" part of WRED. If the maximum threshold-2000KB, for example-is reached, then all incoming packets are dropped until less than 2000KB of buffer space is consumed by the specified traffic. 776 | Quality of Service (QoS)