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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.
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 set 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 500 Mbps of bandwidth. WRR solves the problem that SP
queuing might fail to serve packets in low-priority queues for a long time.
WFQ queuing
Figure 16 WFQ queuing
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 the WRR group (group 1). 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 the WRR group are scheduled based on their weights.
SP+WFQ queuing
You can configure some queues on an interface to use SP queuing and others to use WFQ queuing
by assigning the queues to the SP group and the WFQ group (group 1). With this SP+WFQ queuing
method, the system schedules traffic as follows:
1. The system schedules the traffic conforming to the minimum guaranteed bandwidth in the WFQ
group.
2. The system uses SP to schedule queues in the SP group.
3. If there is remaining bandwidth, the system schedules the traffic of queues in the WFQ group
based on their weights.
Queue 0 Weight 1
……
Queue 1 Weight 2
Queue N-2Weight N-1
Queue N-1 Weight N
Packets to be sent through
this port
Sent packets
Interface
Queue
scheduling
Sending queue
Packet
classification
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