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way, critical service messages are sent preferentially, and non-critical service messages are sent
when the critical service messages are not sent.
Disadvantage of Strict Priority: If there are messages in the queues with higher priority for a
long time during congestion, the messages in the queues with lower priority will keep stuck
because they are not served.
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Weighted Round Robin Mode (WRR)
In this mode, packets in all the queues are sent in order based on the weight value for each
queue and every queue can be assured of a certain service time. Assuming there are 2 egress
queues on the port. The two weight values (namely, w2 and w1) indicate the proportion of
resources assigned to the two queues respectively. On a 100M port, if you set the weight
values of WRR queue-scheduling algorithm to 7 and 3 (correspond to w2 and w1 respectively).
Then the queue with the lowest priority can be ensured of, at least, 30 Mbps bandwidth, thus
WRR queue overcomes the disadvantage of SP queue that the packets in the queues with
lower priority cannot get service for a long time.
In WRR mode, though the queues are scheduled in order, the service time for each queue is
not fixed, that is to say, if a queue is empty, the next queue will be scheduled. In this way, the
bandwidth resources are made full use of.
Egress Discard
Messages are discarded on the egress port when congestion occurs in order to reduce the
loading of the ingress port.
This is applicable to following special scenarios: Both 100 Mbps ports and 1000 Mbps ports
exist when multicast packets are transmitted; perform RFC2889 test. This function is not
recommended in common scenarios.
9.2.2 Configure QoS
1.
Configure QoS mode.
(1) Click Device Management > QoS.
(2) Select a priority mode from the QoS Mode drop-down menu. If WRR is selected, you must
also set Low weight and High weight. Note that the proportion of High must be greater
than that of Low. This series of switches support a proportion of 1-7.
Chapter 9 Device management 31