The Research Of VoIP Based On H.323 Protocol With The Implement In C++

VoIP, or called IP Phone, is a kind of digital telephone technology. Voice information is operated through the process as follows: compression and codec, pack and division, distribution and routing, storage and switch, unpack and decompression and etc, in which way the voice communications over IP network are accomplished. Compared with traditional telephone, IP Phone enhances the efficiency of the band resource and reduces the cost of the voice services. Therefore, IP Phone is developed rapidly over the whole world. Nowadays, it is sure that VoIP is one of the fastest and the most popular service application technologies in the world and also one of the highlights of the modern cyber world.I have made a deep research in VoIP combining with the project of GNSS lab, DLMU and the research target is to provide more efficient and more advanced methods of voice communication for the CTI of the navigation system.This thesis gives the core concepts and important problems concerning the implement of VoIP in detail. In my research and development of VoIP, I choose the ITU-T H.323 protocol as the main protocol and try to anatomize it deeply. I implement the H.225.0, H.245, RTP/RTCP protocols, voice sampling/restore and etc in C++ language. The program steps are as follows: (1) voice processing;(2) H.225 call signal;(3) H.245 control signal;(4) media stream and media stream control;(5) call releasing. Since VoIP is the developing technology, it has some problems to be solved. Therefore, the section about the research of improving the QoS is set in the last chapter. In the last, some current problems of QoS is shown and several concerning resolution methods are introduced and analyzed, among which the design of the jitter buffers and the WSOLA are the two points.In the program test, the result is good. The two PC over the LAN in the lab succeeded to call each other and the voice in them is clear and legible. Also, MOS method is used to rate the quality of voice. On the other hand, in the conclusion r, several problems encountered during the research are concluded and some thought of optimization and improvement of VoIP is provided.