1-10The Switch 4500 series support three queue scheduling algorithms: Strict Priority (SP) queuing,Weighted Fair Queuing (WFQ), and Weighted Round Robin (WRR) queuing.1) SP queuingFigure 1-6 Diagram for SP queuingSP queue-scheduling algorithm is specially designed for critical service applications. An importantfeature of critical services is that they demand preferential service in congestion in order to reduce theresponse delay. Assume that there are eight output queues on the port and the preferential queueclassifies the eight output queues on the port into eight classes, which are queue7, queue6, queue5,queue4, queue3, queue2, queue1, and queue0. Their priorities decrease in order.In queue scheduling, SP sends packets in the queue with higher priority strictly following the priorityorder from high to low. When the queue with higher priority is empty, packets in the queue with lowerpriority are sent. You can put critical service packets into the queues with higher priority and putnon-critical service (such as e-mail) packets into the queues with lower priority. In this case, criticalservice packets are sent preferentially and non-critical service packets are sent when critical servicegroups are not sent.The disadvantage of SP queue is that: if there are packets in the queues with higher priority for a longtime in congestion, the packets in the queues with lower priority will be “starved” because they are notserved.2) WFQ queuing
