H3C S5500-EI series Operation Manual page 1070

Operation Manual – QoS
H3C S5500-EI Series Ethernet Switches
Figure 4-1 Diagram for SP queuing
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 queue-scheduling algorithm
Chapter 4 Congestion Management
4-2