H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 426)

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Excessively high delay will cause retransmission of packets.
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Congestion decreases the effective throughput of the network and the utilization of the network
resources.
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Aggravated congestion will consume a large amount of network resources (especially memory
resources), and unreasonable resource assignment will even lead to system resource deadlock
and cause the system breakdown.
It is obvious that congestion is the root of service performance declination because congestion makes
traffic unable to get resources timely. However, congestion is common in a complicated environment
where packet switching and multi-user services coexist. Therefore, congestion must be treated
carefully.
Countermeasures
Increasing network bandwidth is a direct way to solve the problem of resource insufficiency, but it
cannot solve all the problems that cause network congestion.
A more effective way to solve network congestion problems is to enhance the function of the network
layer in traffic control and resource assignment, to provide differentiated services for different
requirements, and to assign and utilize resources correctly. In the process of resource assignment and
traffic control, the direct or indirect factors that may cause network congestion must be properly
controlled so as to reduce the probability of congestion. When congestion occurs, the resource
assignment should be balanced according to the features and requirements of all the services to
minimize the influence of congestion on QoS.
Major Traffic Management Techniques
Traffic classification, traffic policing, traffic shaping, congestion management, and congestion
avoidance are the foundation for providing differentiated services. Their main functions are as follows:
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Traffic classification: Identifies packets according to certain match rules. Traffic classification is the
prerequisite of providing differentiated services.
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Traffic policing: Monitors and controls the specifications of specific traffic entering the device.
When the traffic exceeds the threshold, restrictive or punitive measures can be taken to protect the
business interests and network resources of the operator from being damaged.
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Congestion management: Congestion management is necessary for solving resource competition.
Congestion management is generally to cache packets in the queues and arrange the forwarding
sequence of the packets based on a certain scheduling algorithm.
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Congestion avoidance: Excessive congestion will impair the network resources. Congestion
avoidance is to supervise the network resource usage. When it is found that congestion is likely to
become worse, the congestion avoidance mechanism will drop packets and regulate traffic to solve
the overload of the network.
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Traffic shaping: Traffic shaping is a traffic control measure to regulate the output rate of the traffic
actively. Traffic shaping regulates the traffic to match the network resources that can be provided
by the downstream devices so as to avoid unnecessary packet loss and congestion.
Among the traffic management techniques, traffic classification is the basis because it identifies packets
according to certain match rules, which is the prerequisite of providing differentiated services. traffic
policing, traffic shaping, congestion management, and congestion avoidance control network traffic and