The Research And Implementation Of Softphone Based On SIP

With the fast development of the computer science and network technology, the voice communication in PSTN will migrate to IP network. VoIP technology provided powerful solutions for voice operations based on IP network. The voice communication using this technology will be one of the development branches of NGN.The Session Initiation Protocol is an application-layer signaling protocol distributed by IETF for creating, modifying, and terminating sessions with one or more participants. By learning the lessons of HTTP and SMTP, reusing many of the header fields, encoding rules and authentication mechanisms of HTTP, and giving a lot of new extensions, SIP provides far lower complexity, rich extensibility and better scalability. SIP is very important in NGN based on softswitch.This thesis describes the principle, core technology and development trend of IP phone in the first part. In the following chapter, we make a detailed analysis on some important protocols and concepts used in SIP softphone, such as signaling control protocol-Session Initiation Protocol, media session parameter negotiation protocol-Session Description Protocol, media transfer protocol-Real-time Transport Protocol, and compared the characteristic of H.323 protocol with SIP protocol from many facets, also analyzed the structure of SIP protocol and working principle of network entities.The thesis laid a strong emphasis on the research of instant message and voice communication. After summarizing the working principle of IP phone and SIP related technologies, the thesis analyzed the JAIN SIP stack and API, also expounded the steps of how to utilize the API to develop user agent. Combined JMF with JAIN SIP technologies, the voice can be transmitted between UA in SIP network. In order to verify the functions, we designed a testing environment in intranet, and got an expected result.In the last part of the thesis, some expectations about SIP development have beenput forward, and also made some suggestions for the further studies.