17QoS techniquesThe QoS techniques include traffic classification, traffic policing, traffic shaping, rate limit, congestionmanagement, and congestion avoidance. They address problems that arise at different positions of anetwork.Figure 4 Placement of the QoS techniques in a networkAs shown in Figure 4, traffic classification, traffic shaping, traffic policing, congestion management, andcongestion avoidance mainly implement the following functions:• Traffic classification—Uses certain match criteria to assign packets with the same characteristics toa class. Based on classes, you can provide differentiated services.• Traffic policing—Polices flows entering or leaving a device, and imposes penalties on traffic flowsthat exceed the pre-set threshold to prevent aggressive use of network resources. You can applytraffic policing to both incoming and outgoing traffic of a port.• Traffic shaping—Proactively adapts the output rate of traffic to the network resources available onthe downstream device to eliminate packet drops. Traffic shaping usually applies to the outgoingtraffic of a port.• Congestion management—Provides a resource scheduling policy to determine the packetforwarding sequence when congestion occurs. Congestion management usually applies to theoutgoing traffic of a port.• Congestion avoidance—Monitors the network resource usage, and is usually applied to theoutgoing traffic of a port. When congestion worsens, congestion avoidance reduces the queuelength by dropping packets.
