User Manual - Configuration Guide (Volume 3)

Chapter 3

Versatile Routing Platform

Congestion Management

Chapter 3 Congestion Management

3.1 Congestion and Congestion Management

3.1.1 About Congestion

For a network unit, if data packets reach the interface at a speed faster than that the interface can transmit the data packets, congestion will occur at this interface. And some packets may be lost if there is no enough space to store them. The loss of data packets will in turn cause the same host or router to redirect the data packets due to timeout, as a result, a vicious circle will happen.

There are many factors to cause congestion. For example, if the packet flow enters the router from a high-speed link and is sent out from a low-speed link, congestion will occur. And if packet flows enter the router from several interfaces at the same time while they are sent out from one interface or the processor speed is slow, congestion will also occur.

As shown in the figure below, two LANs of an enterprise is interconnected through a low-speed link. When a user in LAN1 sends data packets to a user in LAN 2, congestion may occur at the interface that connects the router of LAN 1 with the low- speed link. If an important application is running between the servers of the two LANs, while an unimportant application is running between the two PCs, the important application will be affected.

DDN/FR/ISDN/PSTN

Quidway router

PC

 

Ethernet

 

10 M

Congestion occurs

Company’s LAN 2

 

PC

Server

Quidway router

 

Ethernet

10 M

Company’s LAN 1

Server

Figure QC-3-1Example of congested network

3.1.2 Congestion Management Policy

When congestion occurs, some packets may be discarded if there is no enough buffer to store them. The loss of data packets will in turn cause the same host or router to

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Huawei v200r001 user manual Congestion and Congestion Management, About Congestion, Congestion Management Policy