1-2requested, reserved, and pre-purchased resources. The Inter-Serv model can definitely identify andguarantee QoS for each data flow, and provides the most granularly differentiated QoS.However, the Inter-Serv model imposes extremely high requirements on devices. In a network withheavy data traffic, the Inter-Serv model imposes very great pressure on the storage and processingcapabilities of devices. On the other hand, the Inter-Serv model is poor in scalability, and therefore, it ishard to be deployed in the core Internet network.DiffServ Service ModelDiffServ is a multiple services model that can satisfy diverse QoS requirements. Unlike IntServ,DiffServ does not require an application to signal the network to reserve resources before sending data.DiffServ is easy to implement and extend.All QoS techniques mentioned in this document are based on the Diff-Serv model.QoS Techniques OverviewThe QoS techniques include traffic classification, traffic policing, traffic shaping, line rate, congestionmanagement, and congestion avoidance. The following part briefly introduces these QoS techniques.Positions of the QoS Techniques in a NetworkFigure 1-1 Positions 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 organize packets with different characteristicsinto different classes. Traffic classification is the basis for providing differentiated services.z Traffic policing polices particular flows entering or leaving a device according to configuredspecifications and can be applied in both inbound and outbound directions of a port. When a flowexceeds the specification, some restriction or punishment measures can be taken to preventoverconsumption of network resources.z Traffic shaping proactively adjusts the output rate of traffic to adapt traffic to the network resourcesof the downstream device and avoid unnecessary packet drop and congestion. Traffic shaping isusually applied to the outgoing traffic of a port.
