Chapter 36 Configuring QoS

Understanding QoS

Queueing and Scheduling on Egress Queues

Figure 36-11and Figure 36-12show the queueing and scheduling flowcharts for egress ports.

Note If the expedite queue is enabled, SRR services it until it is empty before servicing the other three queues.

Figure 36-11 Queueing and Scheduling Flowchart for Egress Ports on Catalyst 3750-E Switches

Start

 

Receive packet from

 

the stack ring.

 

Read QoS label

 

(DSCP or CoS value).

 

Determine egress queue

 

number and threshold

 

based on the label.

 

Are thresholds

Yes

being exceeded?

 

No

 

Queue the packet. Service

the queue according to

the SRR weights.

Rewrite DSCP and/or

CoS value as appropriate.

Send the packet

out the port.

Done

Drop packet.

86694

 

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

36-18

OL-9775-02

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Cisco Systems 3750E manual Queueing and Scheduling on Egress Queues, 36-18