Congestion: Causes, Impacts, And Countermeasures; Causes; Impacts - H3C S5810 Series 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, and regulating network traffic. To meet these requirements,
networks must provide more improved services.

Congestion: Causes, Impacts, and Countermeasures

Network congestion is a major factor contributed to service quality degrading on 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
100M
100M>10M
（1）
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 incoming interfaces and are forwarded out an
outgoing interface, whose rate is smaller than the total rate of these incoming interfaces.
When traffic arrives at the line speed, a bottleneck is 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. Congestion is unavoidable in switched networks and multi-user application environments.
To improve the service performance of your network, you must address the congestion issues.
100M
10M
10M
50M
（100M+10M+50M）>100M
（2）
100M
1-2