H3C S7500 Series Operation Manual page 696

Operation Manual – QoS
H3C S7500 Series Ethernet Switches
Packets to be sent
through an interface
Figure 1-5 Diagram for SP queues
The 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 8
output queues on a port and the SP queue scheduling algorithm classifies the 8 output
queues on the port into 8 classes, which are queue7, queue6, queue5, queue4, queue3,
queue2, queue1, and queue0. Their priorities decrease in order.
During the queue scheduling process, the SP algorithm sends packets in the queue
with higher priority strictly following the priority order from high to low. When the queue
with the highest priority is empty, packets in the queue with the second highest 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 packets are not sent.
The disadvantage of the SP queue scheduling algorithm is that: if there are packets in
the queues with higher priority for a long time when congestion occurs, the packets in
the queues with lower priority will be "starved to death" because they are not served.
2) WRR queue
Queue 7
Queue 6
Queue 2 weight 2
......
Queue 1
Queue N - 1 weight N -1
Packet
classifying
Queue 0
1-9
Chapter 1 QoS Configuration
High priority
Forw arding direction
Outbound interface
Serviced queue
Queue
scheduling
Low priority