1-2small-sized or edge networks, but not large-sized networks, for example, the core layer of the Internet,where billions of flows are present.DiffServ ModelThe differentiated service (DiffServ) model is a multiple-service model that can satisfy diverse QoSrequirements. Unlike IntServ, DiffServ does not require an application to signal the network to reserveresources before sending data. DiffServ is easy to implement and extend.All QoS techniques in this document are based on the Diff-Serv model.QoS Techniques OverviewThe QoS techniques fall into traffic classification, traffic policing, traffic shaping, line rate, congestionmanagement, and congestion avoidance. The following part briefly introduces these QoS techniques.Applying QoS Techniques in a NetworkFigure 1-1 Position of the QoS techniques in a networkAs shown in Figure 1-1, traffic classification, traffic shaping, traffic policing, congestion management,and congestion avoidance mainly implement the following functions:z Traffic classification uses certain match criteria to assign packets with the same characteristics to aclass. Based on classes, you can provide differentiated services.z 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.z 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.z 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.z Congestion avoidance monitors the network resource usage and is usually applied to the outgoingtraffic of a port. As congestion worsens, congestion avoidance actively reduces the queue lengthby dropping packets.
