Congestion: Causes, Impacts, And Countermeasures - H3C LS-3100-52P-OVS-H3 Operation Manual

The emerging applications demand higher service performance of IP networks. Better network services
during packets forwarding are required, such as providing dedicated bandwidth, reducing packet loss
ratio, managing and avoiding congestion, regulating network traffic, and setting the precedence of
packets. To meet these requirements, a network must provide more improved services.

Congestion: Causes, Impacts, and Countermeasures

Network congestion is a major factor degrading the service quality of a traditional network. Congestion
is a situation where the forwarding rate decreases due to insufficient resources, resulting in extra delay.
Causes
Congestion easily occurs in complex packet switching circumstances in the Internet. The following
figure shows two common cases:
Figure 1-1 Traffic congestion causes
The traffic enters a device from a high speed link and is forwarded over a low speed link.
The packet flows enter a device from several interfaces at the same rate and are forwarded out an
interface at the same rate as well.
When traffic arrives at the line speed, a bottleneck will be created at the outgoing interface causing
congestion.
Besides bandwidth bottlenecks, congestion can be caused by resource shortage in various forms such
as insufficient processor time, buffer, and memory, and by network resource exhaustion resulting from
excessive arriving traffic in certain periods.
Impacts
Congestion may bring these negative results:
Increased delay and jitter during packet transmission
Decreased network throughput and resource use efficiency
Network resource (memory in particular) exhaustion and even system breakdown
It is obvious that congestion hinders resource assignment for traffic and thus degrades service
performance. The chance of congestion is high in switched networks and multi-user application
environments. To improve the service performance of your network, you must address the congestion
issues.
Countermeasures
A simple solution for congestion is to increase network bandwidth. However, it cannot address all the
problems of congestion.
1-2