3Com WX3000 operation manual Sdwrr

Figure 1-8Diagram for WRR queuing

Queue1	Weight 1
Packets to be sent			Sent packets
through this port	Weight 2
Queue2
Queue 2 weight2
			Interface
……
Queue N-1	Weight N-1
Queue N- 1 weight N-1		Queue	Sending queue
Packet		scheduling
classification
Queue N	Weight N

Queue N weight N

WRR queue-scheduling algorithm schedules all the queues in turn and every queue can be assured of a certain service time. Assume there are eight priority queues on a port. WRR configures a weight value for each queue, which is w7, w6, w5, w4, w3, w2, w1, and w0. The weight value indicates the proportion of obtaining resources. On a 100 M port, configure the weight value of WRR queue-scheduling algorithm to 50, 50, 30, 30, 10, 10, 10, and 10 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0 in order). In this way, the queue with the lowest priority can get 5 Mbps bandwidth at least, and the disadvantage of SP queue-scheduling that the packets in queues with lower priority may not get service for a long time is avoided. Another advantage of WRR queue is that: though the queues are scheduled in order, the service time for each queue is not fixed; that is to say, if a queue is empty, the next queue will be scheduled. In this way, the bandwidth resources are made full use.

3)SDWRR

Comparing with WRR queue, SDWRR queue further optimizes the delay and variation for different queues.

For example, configure the weight value of queue0 and queue1 to 5 and 3 respectively. The processing procedures of WRR and SDWRR are as follows:

z

z

WRR: The packets whose weight value is 3 in queue1 are scheduled only after the packets whose weight value is 5 in the queue0 are scheduled. If there is a wide difference between the weight values of two queues, the queue with high weight value will cause great delay and variation for the queue with low weight value.

SDWRR: Two queues are scheduled in turn. Packets whose weight value is 1 in queue0 are scheduled first, and then packets whose weight value is 1 in queue1 are scheduled. The procedure is repeated until the scheduling for one queue is over, and then SDWRR will schedule packets with the left weight values in the other queue. The detailed scheduling sequence is described in the Table 1-7.

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