Dell PowerConnect FCS624S Configuration Guide - Page 646

17 Scheduling NOTE Queue cycles on the PowerConnect devices are based on bytes. These devices service a given number of bytes (based on weight) in each queue cycle. FES and BI/FI queue cycles are based on packets. The bytes-based scheme is more accurate than a packets-based scheme if packets vary greatly in size. • Strict priority (SP) - SP ensures service for high priority traffic. The software assigns the maximum weights to each queue, to cause the queuing mechanism to serve as many packets in one queue as possible before moving to a lower queue. This method biases the queuing mechanism to favor the higher queues over the lower queues. For example, strict queuing processes as many packets as possible in qosp3 before processing any packets in qosp2, then processes as many packets as possible in qosp2 before processing any packets in qosp1, and so on. • Hybrid WRR and SP - This configurable queueing mechanism combines both the strict priority and weighted round robin mechanisms. The combined method enables the Dell PowerConnect device to give strict priority to delay-sensitive traffic such as VoIP traffic, and weighted round robin priority to other traffic types. By default, when you select the combined SP and WRR queueing method, the Dell PowerConnect device assigns strict priority to traffic in qosp7 and qosp6, and weighted round robin priority to traffic in qosp0 through qosp5. Thus, the Dell PowerConnect device schedules traffic in queue 7 and queue 6 first, based on the strict priority queueing method. When there is no traffic in queue 7 and queue 6, the device schedules the other queues in round-robin fashion from the highest priority queue to the lowest priority queue. NOTE Stackable devices that are operating as members of a stack reserve queue 7 for stacking functions. For more information, see "QoS for stackable devices" on page 595. By default, when you specify the combined SP and WRR queuing method, the system balances the traffic among the queues as shown in Table 102. If desired, you can change the default bandwidth values as shown in the section "Bandwidth allocations of the hybrid WRR and SP queues." on page 607. TABLE 102 Default bandwidth for combined SP and WRR queueing methods Queue Default bandwidth qosp7 qosp6 qosp5 qosp4 qosp3 qosp2 qosp1 qosp0 Strict priority (highest priority) Strict priority 25% 15% 15% 15% 15% 15% (lowest priority) 604 PowerConnect B-Series FCX Configuration Guide 53-1002266-01