Chapter 36 Configuring QoS

Understanding QoS

Queueing and Scheduling Overview

The switch has queues at specific points to help prevent congestion as shown in Figure 36-6and Figure 36-7.

Figure 36-6 Ingress and Egress Queue Location on Catalyst 3750-E Switches

Traffic

Policer

Policer

Classify

Marker

Marker

Ingress queues

 

Egress

Stack ring

queues

 

 

 

 

 

 

 

 

SRR

SRR

Policer Marker

Policer Marker

Figure 36-7 Ingress and Egress Queue Location on Catalyst 3560-E Switches

86691

Traffic

Policer

Policer

Classify

Marker

Marker

Ingress queues

Internal Egress

ring queues

SRR

SRR

Policer

Marker

90563

Policer

Marker

Because the total inbound bandwidth of all ports can exceed the bandwidth of the stack or internal ring, ingress queues are located after the packet is classified, policed, and marked and before packets are forwarded into the switch fabric. Because multiple ingress ports can simultaneously send packets to an egress port and cause congestion, outbound queues are located after the stack or internal ring.

 

 

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

 

 

 

 

 

 

OL-9775-02

 

 

36-13

 

 

 

 

 

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Cisco Systems 3750E manual Queueing and Scheduling Overview, 36-13