3Com 10014299 manual Congestion Management

49 CONGESTION MANAGEMENT

This chapter covers the following topics:

■What is Congestion?

■Congestion Management Policy Overview

■Selecting Congestion Management Policies

■Operating Principle of the Congestion Management Policies

■Configuring Congestion Management

■Congestion Management Configuration Examples

What is Congestion? For a network unit, when the speed of the data packet is faster than the speed at which this interface sends the data packet, congestion occurs on the interface. If not enough memory space can be provided to store these data packets, some of them will be lost. The loss of the data packet can cause the host or router that is sending the data packet to resend this data packet because of a timeout which can cause a communication failure.

There are many factors causing congestion. For example, when the data packet flow enters the router through the high-speed link and is then transmitted through the low speed link, congestion can occur. When the data packet flow enters the router simultaneously from multiple interfaces and is transmitted from one interface or the processor slows down, congestion may occur.

As shown in Figure 217, two LANs of one company are connected with each other through the low speed link. When a user on LAN 1 sends a large number of data packets to a user on LAN 2, it may cause congestion on the interface through which router A of LAN 1 is connected to the low speed link. If an important application is running between the servers of both LANs, while an unimportant application is running between two PCs, the important application will be influenced.