Device Management
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applications such as email and FTP.
2. Strict Priority Mode
Strict Priority Queuing is specially designed to meet the demands of critical services or
applications. When congestion occurs on the network, the system will ask for service
preferentially to reduce response delay.
Then under SP algorithm, the port strictly prioritizes packets from higher priority queue over
those from lower priority queue. Namely, packets in the queue with lower priority are sent
only when the queue with higher priority is empty. Thus High-priority packets are always
processed before those of less priority. Medium-priority packets are always processed
before low-priority packets. The lowest priority queue would be serviced only when highest
priority queues had no packets buffered.
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.
3. Weight Round Robin Mode (WRR)
WRR-Mode: Weight Round Robin Mode. 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 5 (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.
8.2.2 Configuring QoS
Click Device Management > QoS to enter the configuration page.
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