Design And Implementation Of RAS And Call Signalling Based On H.323 Protocol Stack

The Internet developed very quickly. It provides the basement of computer network technology for the implement of the visual communication system. The system is a multimedia communication system that can transport audio,video and data information over IP network, and is the one of focus that people study visual communication system. First, this thesis summarizes the development history and direction of visual communication. Then introduces H.323 protocol stack and system structure firstly, and analyzes H.225.0 protocol. Subsequently, base on these, it introduces the general software scheme of H.323 visual communication system software terminal, and the implementation of H.323 protocol stack independent of any operation system and hardware. Then it gives the detailed design and software realization of RAS and call signalling modules. At last, it expatiates the test and results for these two modules.There are two main functions in H.225.0 protocol. One is to realize RAS signalling protocol, and to complete gatekeeper discovery,endpoint registration,admissions ,bandwidth change, and so on. The other is to realize call signalling protocol, that is to establish H.245 media control channel, or by fast connect procedure and Tunnelling mechanism to establish one or more logical channels.There are some special difficulties on the design of H.225.0 protocol. One is the ASN.1 encoding for RAS and call signalling messages. Another is the implementation for call signalling module by FSM(finite state machine). The last is implementation for Fast Connect and Tunnelling two new mechanisms. These difficulties must be taken into account in the course of design of software and coding.