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Figure 14 SP queuing
In Figure 14, SP queuing classifies eight queues on a port into eight classes, numbered 7 to 0 in
descending priority order.
SP queuing schedules the eight queues in descending order of priority. SP queuing sends packets in
the queue with the highest priority first. When the queue with the highest priority is empty, it sends
packets in the queue with the second highest priority, and so on. You can assign mission-critical
packets to a high priority queue to make sure they are always served first. Common service packets
can be assigned to low priority queues to be transmitted when high priority queues are empty.
The disadvantage of SP queuing is that packets in the lower priority queues cannot be transmitted if
packets exist in the higher priority queues for a long time. In the worst case, lower priority traffic might
never get serviced.
WRR queuing
WRR queuing schedules all the queues in turn to ensure that every queue is served for a certain time,
as shown in Figure 15.
Figure 15
WRR queuing
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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