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a long time in congestion, the packets in the queues with lower priority will be “starved to
death” because they are not served.
Figure 9-4 SP-Mode
2. 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. The weight value indicates the occupied proportion of the resource.
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. The default weight value ratio of TC0, TC1, TC2 and TC3 is 1:2:4:8.
Figure 9-5 WRR-Mode
3. SP+WRR-Mode: Strict-Priority + Weight Round Robin Mode. In this mode, this switch
provides two scheduling groups, SP group and WRR group. Queues in SP group and WRR
group are scheduled strictly based on strict-priority mode while the queues inside WRR
group follow the WRR mode. In SP+WRR mode, TC3 is in the SP group; TC0, TC1 and TC2
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