H3C Technologies H3C S10500 Series Switches - Manual (Page 53)

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Assume a port provides eight output queues. WRR assigns each queue a weight value (represented by
w7, w6, w5, w4, w3, w2, w1, or w0) to decide the proportion of resources assigned to the queue.
On a 100 Mbps port, you can configure the weight values of WRR queuing to 5, 5, 3, 3, 1, 1, 1, and 1
(corresponding to w7, w6, w5, w4, w3, w2, w1, and w0, respectively). In this way, the queue with the
lowest priority can get a minimum of 5 Mbps of bandwidth. WRR avoids the disadvantage of SP queuing,
where packets in low-priority queues can fail to be served for a long time.
Another advantage of WRR queuing is that when the queues are scheduled in turn, the service time for
each queue is not fixed. If a queue is empty, the next queue will be scheduled immediately. This improves
bandwidth resource use efficiency.
WFQ queuing
Figure 17 Schematic diagram for WFQ queuing
WFQ is similar to WRR. The difference between WFQ and WRR is that WFQ supports byte-count and
packet-based scheduling weights. You can use WFQ as an alternative to WRR.
Additionally, WFQ can work with the minimum guaranteed bandwidth as follows:
Compared with WRR, WFQ can work with the minimum guaranteed bandwidth as follows:
• By setting the minimum guaranteed bandwidth, you can make sure that each WFQ queue is
assured of certain bandwidth.
• The assignable bandwidth is allocated based on the priority of each queue (assignable bandwidth
= total bandwidth – the sum of minimum guaranteed bandwidth of each queue).
For example, assume the total bandwidth of a port is 10 Mbps, and the port has five flows, with the
precedence being 0, 1, 2, 3, and 4 and the minimum guaranteed bandwidth being 128 kbps, 128 kbps,
128 kbps, 64 kbps, and 64 kbps, respectively.
• The assignable bandwidth = 10 Mbps – (128 kbps + 128 kbps + 128 kbps + 64 kbps + and 64
kbps) = 9.5 Mbps.
• The total assignable bandwidth quota is the sum of all the (precedence value + 1)s, 1 + 2 + 3 + 4
+ 5 = 15.
• The bandwidth percentage assigned to each flow is (precedence value of the flow + 1)/total
assignable bandwidth quota. The bandwidth percentages for the flows are 1/15, 2/15, 3/15,
4/15, and 5/15, respectively.