Huawei Quidway S3900 Series Operation Manual page 671

Operation Manual - QoS&QoS Profile
Quidway S3900 Series Ethernet Switches-Release 1510
Packets sent via this Packets sent via this Packets sent via this
interface interface interface
Figure 1-5 Diagram for SP queues
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 the port and the preferential queue 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.
In the 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 to death" because they are not served.
2) WFQ queue
high priority high priority high priority
Classify Classify Classify
Low priority Low priority Low priority
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1-9
Chapter 1 QoS Configuration
queue 7 queue 7 queue 7
queue 6 queue 6
Packets sent Packets sent Packets sent
queue 5 queue 5
queue 4 queue 4
Dequeue Dequeue Dequeue Sending queue Sending queue Sending queue
queue 3 queue 3
queue 2 queue 2
queue 1 queue 1
queue 0 queue 0