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.