The Design And Implementation Of VoIP System Based On SIP

At present, with the tremendous development of the computer network technology and the communication technology as well as thorough and popular application of multimedia, real-time audio/video communication based on Internet, namely VoIP, has become a popular research topic of Internet application. The realization of VoIP system involves a series of questions, such as: the voice compression coding, the signaling dispatch, passing through NAT and firewall and so on. This paper takes Microsoft outsource as a background, the requirement of project is implement of passing through Intranet in voice communication of MSN Messenger , namely we shall design a VoIP communication module which is set into MSN Messenger. Through thorough research of entire realization process, we have obtained a series of research achievement. The main content includes:1. This paper compares H.323 with SIP in advantages and disadvantages thoroughly, and analyzes the reasons why we select SIP. Then the paper relates concept and characteristic of SIP and SDP, as well as SIP message format and dispatcher process in detail. Finally, the paper study concept and principle of NAT, and discusses the influence which is created to SIP by NAT.2. In the realization of foundation, this paper discusses Windows multithread processing and realization process of Socket thoroughly, and researches working flow of voice network transmission. Then the paper unifies preliminary audio function and callback function, and designs the data structures which can be used in voice transmission, in this way, audio data collection and audio broadcast can be realized. Finally, the paper gives realization steps of audio compression and decompression.3. In the realization of dispatch level, this paper studies the object of RTC Client API thoroughly, and employs foundation function, which has been already compiled, to make the client into ready state. Then the paper use SIP which has been encapsulated in RTC Client API to realized signaling dispatches.4. In the realization of passing through module, this paper analyzes advantages and disadvantages of several kinds of passing through scheme which has been used at present, and relates in detail the reasons why we select STUN. Then the paper designs the function RTCPortManager(), which uses STUN to get the IP address and the port mapping relation, and revises message content of SIP and SDP to implement...