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Catalyst 3560 Switch Software Configuration Guide
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Chapter 28 Configuring QoS
Understanding QoS
Queueing and Scheduling on Egress Queues
Figure 28-8 shows the queueing and scheduling flowchart for egress ports.
Note If the expedite queue is enabled, SRR services it until it is empty before servicing the other three queues.
Figure 28-8 Queueing and Scheduling Flowchart for Egress Ports
Each port supports four egress queues, one of which (queue 1) can be the egress expedite queue. These
queues are assigned to a queue-set. All traffic exiting the switch flows through one of these four queues
and is subjected to a threshold based on the QoS label assigned to the packet.
90565
Receive packet from
the internal ring.
Read QoS label
(DSCP or CoS value).
Determine egress queue
number and threshold
based on the label.
Are thresholds
being exceeded?
Send the packet
out the port.
Queue the packet. Service
the queue according to
the SRR weights.
Drop packet.
Start
Done
Ye s
No
Rewrite DSCP and/or
CoS value as
appropriate.
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