Operation Manual – QoS/ACLH3C S9500 Series Routing Switches Chapter 2 QoS Configuration2-4Packets sent via thisinterfacehigh priorityLow priorityClassifyPackets sentSending queueDequeuequeue 7queue 6queue 5queue 4queue 3queue 2queue 1queue 0Figure 2-4 Priority queuesSP algorithm is designed for key services. One of the characteristics of key services isthese services should be processed first to minimize response delay during switchcongestion. For example, there are eight outbound queues at the port, numberedrespectively as 7 to 0, with priority levels in descending order.In SP mode, the system first sends those packets of higher priority in strict accordancewith priority order. Only when packets in high priority queue are all sent can those inlower priority queue be sent. This manner of putting key-service packets into highpriority queue and non-key service packets into low priority queue does ensure thatkey-service packets are sent first, while non-key service packets are sent during theinterval when no key-service packets needs to be processed.SP algorithm also has its disadvantages: If high priority queues are full, then packetsfrom the low priority queues may not be forwarded.2) WRR algorithmEach port supports eight outbound queues except that port of XP4 card only supportsfour queues. In WRR mode, the system processes the queues by turn, so every queuecan have a service period.See the case where the port supports eight outbound queues. Every queue is assignedwith a weight value (respectively numbered as w7, w6, w5, w4, w3, w2, w1 and w0),which indicates the weight in obtaining resources. For a 100 Mbps port, the weightvalues are set as 50, 30, 10, 10, 50, 30, 10 and 10 (corresponding respectively to w7,w6, w5, w4, w3, w2, w1 and w0). The even the queue with the lowest priority can beallocated with a 5 Mbps bandwidth.
