3Com 2928 User Guide - Page 467

SP queuing SP queuing is specially designed for mission-critical applications, which require preferential service to reduce response delay when congestion occurs. Figure 2-6 Schematic diagram for SP queuing A typical switch provides eight queues per port. As shown in Figure 2-6, SP queuing classifies eight queues on a port into eight classes, numbered 7 to 0 in descending priority order. SP queuing schedules the eight queues strictly according to the descending order of priority. It sends packets in the queue with the highest priority first. When the queue with the highest priority is empty, it sends packets in the queue with the second highest priority, and so on. Thus, you can assign mission-critical packets to the high priority queue to ensure that they are always served first and common service (such as Email) packets to the low priority queues to be transmitted when the high priority queues are empty. The disadvantage of SP queuing is that packets in the lower priority queues cannot be transmitted if there are packets in the higher priority queues. This may cause lower priority traffic to starve to death. WRR queuing WRR queuing schedules all the queues in turn to ensure that every queue can be served for a certain time, as shown in Figure 2-7. 2-7