3com WX3000 User Manual

 

1-12 

Figure 1-8 Diagram for WRR queuing 

Packets to be sent 

through this port

Packet 

classification

Queue 

scheduling

Queue 2  weight 2

Queue N- 1    weight  N-1

Queue N  weight N

Sent packets

Sending queue

Interface

……

Queue 1  

Queue 2    Weight 2

Queue N-1   Weight  N-1

Queue N 

 Weight  N

Weight 1

 

 

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 

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. 

z 

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 

.