Deploying QoS in a network
Figure 3: Position of the QoS techniques in a network
As shown in Figure 3, 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 class. Based on classes, you can provide differentiated services.
Traffic policing—Polices flows entering or leaving a device, and imposes penalties on traffic flows that exceed the preset threshold 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.