Service Model

IntServ is one service model that can provide various service types. It can meet various QoS requirements. Before sending packets, the service model needs to apply for the specified service resources from the network. The request is completed via the RSVP signaling. RSVP applies for the network resources for the application before the application program starts to send packets, so it belongs to the out-band signaling. Before sending data, the application program first informs the network of its own traffic parameters and the needed specified service quality request, including bandwidth, delay and so on. After receiving the resource request of the application program, the network executes the resource distributing check, that is, judge whether to distribute resources for the application program based on the resource application of the application program and the present resources of the network. Once the network confirms to distribute resources for the application program, the network maintains one state for the specified flow (Flow, confirmed by the IP addresses, port numbers and protocol numbers of the two sides) and executes the packet classification, traffic monitoring, queuing and scheduling based on the state. After receiving the confirming information of the network (that is, confirm that the network already reserves resources for the packets of the application program), the application program can send packets. As long as the packets of the application program are controlled within the range described by the traffic parameters, the network will undertake to meet the QoS requirements of the application program.

DiffServ classifies the communications according to the service requirements, and then processes the ingress and egress packets according to the classification result, so as to ensure that the network is always in the good communication connection status. It is one multi-channel service model and can meet the QoS requirements of different flows. The largest difference with IntServ is that DiffServ can reserve resources in the network without signaling exchange. It just functions on one port of one transmission device in the network, processing the ingress and egress packets of the port. DiffServ does not need to maintain the status information for each kind of communication. It distinguishes the QoS level of each packet according to the configured QoS mechanism and provides the service for the packet according to the level. Therefore, the mechanism providing the QoS scheme is also called CoS. There are many classification methods and the common modes are to classify according to the priority of the IP packet, classify according to the source, destination address and port of the packet, classify according to the packet protocol, classify according to the packet size and packet ingress port, and so on.

Priority mapping, flow classification, traffic monitoring, traffic shaping, congestion management and congestion avoidance are the main components of DiffServ. The flow classification identifies the packets according to some matching rules and is the basis and premise of DiffServ; traffic monitoring, traffic shaping, congestion management and congestion avoidance distribute and schedule the resources for the network traffic from different aspects and they are the embodiment of the DiffServ idea.