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QoS techniques overview
The QoS techniques include traffic classification, traffic policing, traffic shaping, line rate, congestion
management, and congestion avoidance. The following section briefly introduces these QoS techniques.
Deploying QoS in a network
Figure 2 Position of the QoS techniques in a network
As shown in Figure 2, traffic classification, traffic shaping, traffic policing, congestion management, and
congestion avoidance mainly implement the following functions:
• Traffic classification—Uses certain match criteria to assign packets with the same characteristics to
a traffic class. Based on traffic classes, you can provide differentiated services.
• Traffic policing—Polices flows entering or leaving a device, and imposes penalties on traffic flows
to prevent aggressive use of network resources. You can apply traffic policing to both incoming and
outgoing traffic of a port.
• Traffic shaping—Proactively adapts the output rate of traffic to the network resources available on
the downstream device to eliminate packet drops. Traffic shaping usually applies to the outgoing
traffic of a port.
• Congestion management—Provides a resource scheduling policy to determine the packet
forwarding sequence when congestion occurs. Congestion management usually applies to the
outgoing traffic of a port.
• Congestion avoidance—Monitors the network resource usage, and is usually applied to the
outgoing traffic of a port. When congestion worsens, congestion avoidance reduces the queue
length by dropping packets.
QoS processing flow in a device
Figure 3 briefly describes how the QoS module processes traffic:
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