Research And Realization Of NET2NET VoIP System Terminal's Solution

VoIP, also known as network phone or IP phone, refers to the technology of using IP network to transmit voice. For its low price and high efficiency of using Internet resource, VoIP has a bright future. H.323 and SIP are two main signaling protocols to realize VoIP. They have similar functions. But compared with H.323, SIP is proved to be more easy in call flow and function extension. Therefore, researching the design and realization of VoIP system based on SIP will be meaningful in practical usage.The subject of this paper comes from Secomity company's NET2NET VoIP project, which aims at realizing a VoIP system with the functions like user authentication, point-to-point voice communication, call transfer, NAT traversal, etc.. This paper focuses on terminal's solution.The paper first discussed VoIP's work principle, key technologies and realization modes. Then explained SIP's architecture, message syntax and signaling flow in details. It also introduced other protocols used in VoIP, like SDP, RTP and RTCP.Based on the above research, the following part of this paper mainly analyzes VoIP terminal's solution. According to functional commands, it made software's module design principle, and showed how to realize server communication module, SIP module, audio process module and NAT traversal module concretely. Then, the paper gave terminal's flow design method. It analyzed how to initialize the application and how to realize the required services in this charpter. The paper also made a brief explaination on the test result. The test indicated that, the terminal software can cooperate with certain USB phone to realize VoIP function.In the end, the paper proposed the deficiency in research and future work.