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.
The Switch Series supports byte-count weight (which determines the weight by the number of bytes
scheduled in a cycle) or packet-based weight (which determines the weight by the number of packets
scheduled in a cycle).
Take the byte-count weight as an example. On a 1000 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 50 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.
Figure 17 WFQ queuing
WFQ is similar to WRR. You can use WFQ as an alternative to WRR.
Additionally, 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.