4000 Router Series ACL and QoS Configuration Guide

Configuring congestion management

Overview

Causes, impacts, and countermeasures of congestion

Congestion occurs on a link or node when traffic size exceeds the processing capability of the link or

node. It is typical of a statistical multiplexing network and can be caused by link failures, insufficient

resources, and various other causes. Figure 13 sh

ows common congestion scenarios.

Figure 13 Traffic congestion causes

Congestion can introduce the following negative results:

• Increased delay and jitter during packet transmission.

• Decreased network throughput and resource use efficiency.

• Network resource (memory, in particular) exhaustion and system breakdown.

Congestion is unavoidable in switched networks or multiuser application environments. To improve the

service performance of your network, implement congestion management policies.

For example, congestion management defines a resource dispatching policy to prioritize packets for

forwarding when congestion occurs.

Congestion management policies

Congestion management involves queue creating, traffic classification, packet enqueuing, and queue

scheduling.

Queuing is a common congestion management technique. It classifies traffic into queues and picks out

packets from each queue by using a certain algorithm. Various queuing algorithms are available, and

each addresses a particular network traffic problem. Your choice of algorithm significantly affects

bandwidth assignment, delay, and jitter.

This section describes several common queue-scheduling mechanisms.