Cisco Systems 3750E manual Queueing and Scheduling on Ingress Queues, 36-15

Chapter 36 Configuring QoS

Understanding QoS

In shared mode, the queues share the bandwidth among them according to the configured weights. The bandwidth is guaranteed at this level but not limited to it. For example, if a queue is empty 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 36-71, the “Configuring SRR Shaped Weights on Egress Queues” section on page 36-78, and the “Configuring SRR Shared Weights on Egress Queues” section on page 36-79.

Queueing and Scheduling on Ingress Queues

Figure 36-9and Figure 36-10show the queueing and scheduling flowcharts for ingress ports.

Figure 36-9 Queueing and Scheduling Flowchart for Ingress Ports on Catalyst 3750-E Switches

Start
Read QoS label
(DSCP or CoS value).
Determine ingress queue
number, buffer allocation,
and WTD thresholds.
Are thresholds	Yes
being exceeded?
No

Queue the packet. Service

the queue according to

the SRR weights.

Drop packet.

Send packet to the stack ring.

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	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		36-15