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Catalyst 2960 Switch SoftwareConfiguration Guide
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Chapter29 Configuring QoS
Understanding QoS
In shared mode, the queues share the bandwidth among them accord ing to the configured weights. The
bandwidth is guaranteed at this level but not limited to it. For example, if a queue is emp ty and no longer
requires a share of the link, the remaining queues can expand into the unused bandwidth and share it
among them. With sharing, the ratio of the weights controls the frequency of dequeuing; the absolute
values are meaningless.
For more information, see the “Allocating Bandwidth Between the Ingress Queues” section on
page 29-60, the “Configuring SRR Shaped Weights on Egress Queues” section on page 29-66, and th e
“Configuring SRR Shared Weights on Egress Queues” section on page 29-67.
Queueing and Scheduling on Ingress Queues
Figure 29-7 shows the queueing and scheduling flowchart for ingress ports.
Figure29-7 Queueing and Scheduling Flowchart for Ingress Ports
Note SRR services the priority queue for its configured share before servicing the other queue.
90564
Read QoS label
(DSCP or CoS value).
Determine ingress queue
number, buffer allocation,
and WTD thresholds.
Are thresholds
being exceeded?
Queue the packet. Service
the queue according to
the SRR weights.
Send packet to
the internal ring.
Drop packet.
Start
Yes
No