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Figure 476 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 incoming interfaces and are forwarded out of an
outgoing interface, whose rate is smaller than the total rate of the incoming interfaces.
When traffic arrives at the line speed, a bottleneck is created at the outgoing interface, which causes
congestion.
Congestion can also be caused by resource shortage, such as insufficient processor time, buffer, and
memory, and by network resource exhaustion resulting from excessive arriving traffic in specific periods.
Impacts
Congestion may introduce the following negative results:
• Increased delay and jitter during packet transmission
• Decreased network throughput and resource use efficiency
• Network resource (memory in particular) exhaustion and system breakdown
Congestion hinders resource assignment for traffic and degrades service performance. Congestion is
unavoidable in switched networks and multi-user application environments.
Countermeasures
A simple solution for congestion is to increase network bandwidth. However, it cannot solve all the
problems that cause congestion because you cannot infinitely increase network bandwidth.
A more effective solution is to provide differentiated services for different applications through traffic
control and resource allocation. In this way, resources can be used more effectively. During resource
allocation and traffic control, direct or indirect factors that might cause network congestion should be
controlled to reduce the probability of congestion. Once congestion occurs, resource allocation should
be performed according to the characteristics and demands of applications to minimize the effects of
congestion.
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