HP 5920 Configuration Manual page 51

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 implements the weight of a queue by scheduling a certain number of bytes (byte-count WRR)
or packets (packet-based WRR) for that queue. Take byte-count WRR as an example: On a 10 Gbps port,
you can configure the weight values of WRR queuing to 5, 3, 1, 1, 5, 3, 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 500 Mbps of bandwidth. WRR solves the problem that SP queuing may fail to serve
packets in low-priority queues 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.
The switch supports WRR groups. You can assign an output queue to WRR group 1 or WRR group 2.
Queues in a WRR group are scheduled according to the configured weights, and WRR groups are
scheduled at a 1:1 ratio.
WFQ queuing
Figure 16 WFQ queuing
Packets to be sent through
this port
WFQ is similar to WRR. The difference is that WFQ enables you to set guaranteed bandwidth that a
WFQ queue can get during congestion.
SP+WRR queuing
You can configure some queues on an interface to use SP queuing and others to use WRR queuing by
assigning the queues to the SP group and WRR groups (group 1 and group 2). With this SP+WRR
queuing method, the system first schedules the queues in the SP group and then schedules queues in the
WRR group when all queues in the SP group are empty. The queues in the SP group are scheduled based
on their priorities. The queues in a WRR group are scheduled based on their weights, and the two WRR
groups are scheduled at a 1:1 ratio.
SP+WFQ queuing
You can configure SP+WFQ queuing by assigning some queues to the SP group and others to the WFQ
groups (group 1 and group 2). With this SP+WFQ queuing method, the system schedules first the queues
in the SP group based on their priorities and then the queues in WFQ groups. When scheduling WFQ
groups, the system schedules first the traffic conforming to the minimum guaranteed bandwidth of each
Queue 0 Weight 1
Queue 1 Weight 2
......
Queue N-2 Weight N-1
Packet
classification
Queue N-1 Weight N
Sent packets
Queue Sending queue
scheduling
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Interface