Configuring Quality of Service
Configuring QoS
Cisco Small Business 300 Series Managed Switch Administration Guide 251
18
Configuring QoS Queues
The switch supports four queues for each interface. Queue number four is the
highest priority queue. Queue number one is the lowest priority queue.
There are two ways of determining how traffic in queues is handled, Strict Priority
and Weighted Round Robin (WRR).
Strict Priority—Egress traffic from the highest-priority queue is transmitted first.
Traffic from the lower queues is processed only after the highest queue has been
transmitted, thus providing the highest level of priority of traffic to the highest
numbered queue.
Weighted Round Robin (WRR)—In WRR mode the number of packets sent from
the queue is proportional to the weight of the queue (the higher the weight the
more frames are sent). For example, if all four queues are WRR and the default
weights are used, queue1 receives 1/15 of the bandwidth (assuming all queues
are saturated and there is congestion), queue 2 receives 2/15, queue 3 receives 4/
15 and queue 4 receives 8 /15 of the bandwidth. The type of WRR algorithm used
in the device is not the standard Deficit WRR (DWRR), but rather Shaped Deficit
WRR (SDWRR).
The queuing modes can be selected in the
Queue Page.
When the queuing mode
is by strict priority, the priority sets the order in which queues are serviced,
starting with queue_4 (the highest priority queue) and going to the next lower
queue when each queue is completed.
When the queuing mode is Weighted Round Robin, queues are serviced until their
quota has been used up and then another queue is serviced.
It is also possible to assign some of the lower queues to WRR, while keeping some
of the higher queues in strict priority. In this case traffic for the strict priority
queues is always sent before traffic from the WRR queues. Only after the strict
priority queues have been emptied is traffic from the WRR queues forwarded.
(The relative portion from each WRR queue depends on its weight).
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