85
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
can not 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 belong
to the WRR group and the weight value ratio of TC0, TC1 and TC2 is 1:2:4. In this way, when
scheduling queues, the switch allows TC3 to occupy the whole bandwidth following the SP
mode and the TC0, TC1 and TC2 in the WRR group will take up the bandwidth according to
their ratio 1:2:4.
4. Equ-Mode: Equal-Mode. In this mode, all the queues occupy the bandwidth equally. The
weight value ratio of all the queues is 1:1:1:1.
