In order to deploy QoS appropriately there is a fundamental apsect which determines the type QoS model you deploy.
Essentially different platfroms support different methods for congestion avoidance, prioritising and schuleding, and therefore governs your approach.
SRR is different from WRR in that the SRR algorithm provides a way to shape outbound traffic to a stated rate. In some respects, it is similar to a policer except that traffic in excess of the rate will be buffered rather than dropped as with a policer.
The shaper is implemented on a per-queue basis and has the effect of smoothing transient bursts of data that pass through that port.
SRR also modifies the way in which it schedules data when compared to the WRR algorithm.
WRR will service each queue by the weight, therefore the queue with the higher weight will be serviced before others. Whereas SRR will service each queue starting with the highest to the lowest weight.
The purpose of a strict priority queue is to ensure that latency sensitive traffic serviced before others queues.
When a packet is placed into a strict priority queue, scheduling of packets from WRR queues will cease, and the packet(s) in the strict priority queue will be transmitted. Only when the strict priority queue is empty will the scheduling process recommence sending packets from WRR queues.
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Regards
Allan.
