1, Introduction Network architecture evolution and the development of broadband technology to promote and accelerate the traditional networks to next generation network (NGN) evolution. As the network expansion of the scale, the gradual expansion of applications, particularly real-time requirements of new services (such as VoIP, video conferencing, multimedia, distance learning, video on demand etc.) continue to occur, also requires efficient communication networks to provide end to end service quality support; the same time users on the network quality of service (QoS, QualityofService) demand higher and higher. Therefore, how to provide end to end QoS will be one of the core NGN.
2, NGN architecture and QoS issues
2.1NGN system of institutions NGN is a softswitch, using open, standard architecture to provide voice, video, data and other services.
Softswitch technology is the core technology of next generation business network, NGN is a key technology. The basic meaning of softswitch call control is to separate from the media gateway through the server software for basic call control functions, including call routing, management, control, connection control, (establish a session to remove the session), and protocol interworking. Softswitch is the main design business / control and transmission / access separation between the various entities connected via standard protocols and communication, whose main functions include the following components: 1) call control functions; 2) to provide business functions; 3 ) Service Switching Function; 4) interworking function; 5) SIP proxy function; 6) billing functions; 7) network management functions; 8) routing, address resolution, and authentication; 9) H.248 terminals, SIP terminals, MGCP terminal control and management functions; 10) on the 7th signaling (ie, MTP and its application part) functions; 11) H.323 terminal control, management function (optional).
Softswitch functional structure shown in Figure 1.
Figure 1 Schematic diagram of soft switch system
2.2NGN the QoS problem The QoS, the soft-switched network and the Internet there are two important differences. First, the soft-switched network is a multimedia communications network, not only to support the IP network, traditional data applications, and to support high-quality real-time audio and video communication services. Second, the soft-switched network is a network of commercial operation, the necessary commitment to provide service quality, and the need to provide Quality of Service based billing. Therefore, depending on the application needs to provide appropriate QoS.
In technology, soft switch networks and traditional GSTN is also very different. GSTN is the circuit-switched network, when a large network telephone traffic to a certain extent, due to all the network resources are occupied, then the switch will reject the call request. Reject a call affects only one user, for the ongoing calls are not in any way. Soft-switched network is a resource statistical multiplexing of packet networks, when network traffic increases, network congestion occurs resource use, although the follow-up calls can still access the network, but the QoS will decrease, not only that, the ongoing call QoS will be affected. Therefore, the soft-switching network QoS problems than GSTN in much more complex.
In NGN to achieve end to end QoS, including the following: the meaning of end to end, boundary location, UNI range; the definition of end to end multimedia QoS level and a single media stream QoS class registration form; access control and resource management, including physical and application layer network level interoperability between entities; specify the net with a low-level QoS mechanisms to obtain high-level of QoS and QoS control low-level domain.
3, QoS framework of the model and key technologies
3.1QoS framework model NGN framework to support QoS model for the control of the core is a series of network performance, prevent network resource contention of the module, can be summarized as design of various planar integrated technology: management plane, control plane and data plane, such as Figure 2.
Figure 2 QoS Framework Model Management plane: need to define the SLS, management strategies and metrics by which allocation of resources across the network.
Control plane: the need for admission control, traffic engineering to support QoS routing and resource reservation.
Data plane: the data stream needs shaping, control line and a series of processing, and implementation of buffer management and congestion avoidance control.
3.2QoS the key technologies 3.2.1 Integrated Service model and resource reservation protocol (IntServ / RSVP)
IntServ / RSVP service model defined in IETFRFC1633 carried out. RFC1633 RSVP to RSVP IntServ structure as the main signaling protocol. The basic idea is to resource reservation on the way to achieve the QoS guarantee, RSVP is the core part.
In the service level, IntServ / RSVP offers 3 levels of service:
1) end of the quality assurance-based services: guaranteed bandwidth, delay limits, no packet loss.
2) controlled load-based service: similar to a load in the current network in light of the best of what we achieve quality of service business.
3) best effort service: similar to the current Internet to provide the best of what we service.
At the structural level, IntServ / RSVP service model mainly consists of four parts: the signaling protocol RSVP, access controller, classifier and packet scheduler.
In achieving the level, the Integrated Services requires that all routers in the control path processing signaling messages for each stream and maintain the state of each flow path and resource reservation status, the data path to perform flow classification, scheduling and buffer management. Specifically, the resource reservation protocol RSVP for point by point to create or remove each stream resource reservation soft state, namely the establishment or removal of data transmission paths; access controller node according to the link and network resources usage and QoS request for the specific requirements, to decide whether to accept a resource reservation request; classification of the transmitted data packets are classified into a transmission stream, IntServ commonly used classification is multi-domain classifier, when the router receives a packet, it According to the Ministry of multiple header fields into the appropriate packet queue; scheduler under different policies on different queue scheduling data packets transmitted.
IntServ / RSVP can provide rigorous fine-grained quality of service end to end, but the extension is poor, with high requirements on network nodes require the source to destination