1-12In 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) WRR queuingFigure 1-8 Diagram for WRR queuingWRR queue-scheduling algorithm schedules all the queues in turn and every queue can be assured ofa certain service time. Assume there are four output queues on a port. WRR configures a weight valuefor each queue, which is w3, w2, w1, and w0 for queue 3 through queue 0. The weight value indicatesthe proportion of obtaining resources. On a 100 M port, configure the weight value of WRRqueue-scheduling algorithm to 5, 3, 1, and 1 (corresponding to w3, w2, w1, and w0 in order). In this way,the queue with the lowest priority can get 10 Mbps bandwidth (100-Mbps × 1/ (5 + 3 + 1 + 1)) at least,and the disadvantage of SP queue-scheduling that the packets in queues with lower priority may not getservice for a long time is avoided. Another advantage of WRR queue is that: though the queues arescheduled in order, the service time for each queue is not fixed; that is to say, if a queue is empty, thenext queue will be scheduled. In this way, the bandwidth resources are made full use.3) HQ-WRR queuingHQ-WRR is an improvement over WRR. Assume there are four priority queues on a port and queue 3allocated with the highest priority, the switch will ensure that this queue get served first and will performround-robin scheduling to the other three queues when the traffic has exceeded the bandwidth capacityof a port.Flow-Based Traffic AccountingThe function of traffic-based traffic accounting is to use ACL rules in traffic classification and performtraffic accounting on the packets matching the ACL rules. You can get the statistics of the packets youare interested in through this function.
