Huawei Quidway S3500 Series Operation Manual page 362

Operation Manual - QoS/ACL
Quidway S3500 Series Ethernet Switches
Packets sent via this
interface
Figure 2-1 SP
The SP is specially designed for the key service application. A significant feature of the
key service is requiring for priority to enjoy the service to reduce the responding delay
when congestion occurs. Take 4 egress queues for each port as example, SP divides
the queue of port into up to 4 kinds, high-priority, medium-priority, normal-priority and
low-priority queues (which are shown as the Queue 3, 2, 1 and 0 in turn) with
sequentially reduced priority.
During the progress of queue dispatching, strictly following the priority order from high
to low, the SP gives preference to and sends the packets in the higher-priority queue
first. When the higher-priority queue is empty
lower-priority group. In this way, put the packets of higher priority service in the
higher-priority queue and put the packets of lower priority, like e-mail, in the
lower-priority queue, can guarantee the key service packets of higher priority are
transmitted first, while the packets of lower service priority are transmitted during the
idling gap between transmitting the packets of higher service priorities.
The SP also has the drawback that when congestion occurs, if there are many packets
queuing in the higher-priority queue, it will require a long time to transmit these packets
of higher service priority while the messages in the lower-priority queue
continuously set aside without service.
2) WRR
The round scheduling ensures every queue gets some time of service of the switch port.
Take 4 egress queues for each port as example, WRR gives every queue a weight (w3,
w2, w1, and w0 respectively) for resource obtaining. For example, you can configure
the weight value of the WRR algorithm for 100M port as 50, 30, 10, 10 (corresponding
to the w3, w2, w1 and w0 respectively). Thus the low-priority queue can be guaranteed
to get the minimum bandwidth of 10Mbps, avoiding the case in SP scheduling that the
messages in the lower-priority queues may not get any service for long time. Another
advantage of WRR queue is that the service time is assigned to each queue flexibly,
although it is the round multiple queue scheduling. When a queue is empty, it will switch
to the next queue immediately, thereby making good used of the bandwidth resource.
high queue
middle queue
normal queue
Classify
bottom queue
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2-3
Chapter 2 QoS Configuration
Packets sent
Sending queue
Dequeue
it will send the packets in the
are