Research Of The UserAgent Of SIP Open Source Based On Vocal

With the high development of internet and digital communication,the IP-based communication mode is more and more popular.Session Initiation Protocol(SIP)provides a new application space to VoIP(Voice over IP)with its simplicity,agility,high efficiency,nicer expansibility and compatibility.VoIP communication controlling system can mainly be described as H.323 of ITU-T and SIP of IETE SIP is an application-layer protocol,which can establish,modify and terminate multimedia sessions(conferences),such as internet telephony calls.This paper particularly researches the designments and implements of User Agent in VOCAL-the open source codes of SIP,and designs material achievement.The result of tests shows the SIP system runs stably and has right work state to communicate with each other.This paper firstly studies the functions of SIP with comparison to H.323, discussing the current status and development trend of SIP.According to RFC3261,it analyzes deeply into the system structure of SIP protocol.Based on the mature open source codes named Vovida Open Communication Library (VOCAL)about SIP,this paper derive how the SIP stack is implemented from such a detailed project.The purpose of this thesis is to explore the User Agent and emphasizes base classes about building the whole system.Furthermore,it realizes the constructer of SIP and the UA calling procedure.The author works out the designment of three independent and subsequent threads to manage the sending and receiving of SIP messages,the detecting of external input,and the operating of events.This design is advantageous in the process of efficiently loading new services.Eventually the author modifies the source codes of UA mainly on repairing some bugs,and add own understanding to SIP.First adding user-defined event processes to make the whole calling more perfect.Next,due to all the UA is touched off by event-driven,additional interfacial operation is easier to use.Meanwhile because of audio data without contraction in the UA and bandwidth waste,adding a module,called media manager,to manage the various media form,including audio(G.729A)& video(H.263).It makes it become an IP communication terminal based on VOCAL.The thesis tests for the system in the end.The result shows the SIP system runs stably,and achieves the requirements for all functions in the design.Finally, this article sums up the main points of research and raises the future work.