3Com WX3000 operation manual 7Diagram for SP queuing

1)SP queuing

Figure 1-7Diagram for SP queuing

Queue 7
	High priority
Packets to be sent
through this port		Sent packets
Queue 6
Queue 2 weight2
		Interface
……
Queue 1
Queue N- 1 weight N-1	Queue	Sending queue
Packet	scheduling
classification
Queue 0
Queue N weight N	Low priority

SP queue-scheduling algorithm is specially designed for critical service applications. An important feature of critical services is that they demand preferential service in congestion in order to reduce the response delay. Assume that there are eight output queues on the port and the preferential queue classifies the eight output queues on the port into eight classes, which are queue7, queue6, queue5, queue4, queue3, queue2, queue1, and queue0. Their priorities decrease in order.

In queue scheduling, SP sends packets in the queue with higher priority strictly following the priority order from high to low. When the queue with higher priority is empty, packets in the queue with lower priority are sent. You can put critical service packets into the queues with higher priority and put non-critical service (such as e-mail) packets into the queues with lower priority. In this case, critical service packets are sent preferentially and non-critical service packets are sent when critical service groups are not sent.

The disadvantage of SP queue is that: if there are packets in the queues with higher priority for a long time in congestion, the packets in the queues with lower priority will be “starved” because they are not served.

2)WRR queuing

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