Softswitch Research And Implementation Of The Communication Protocol (sip)

With the rapid development of computer and communication technology , the main trend is that NGN(Next Generation Network) which is based on IP network and soft switch core technology will replace the existing communication networks. Under the background , IETF's SIP(Session Initiation Protocol) can provide an excellent support to the multimedia communication session management as a soft switch application layer's protocol . We can build a low cost, multi-service, high adding value multimedia communication network with it and other protocols from IETF .The system can also support terminal user's mobility very well.Firstly, the thesis introduces SIP's applicative background , function specialities, cooperating protocols .And based on the newest protocol specification , the thesis analyses its architecture , grammar ,session call flow and expansibility in detail .After this , according to the software engineering 's module developing principle, implement a standard protocol stack .Then the thesis explain its core aspect : transaction layer , transaction user layer ,and the interface between them . It has included the basic functions of user terminals , we can implement other different function entities such as: SIP porxy server, SIP register server by adding different transaction user layers. After the software's compiling and debuging, we build a simple applicative environment to test and verify its basic functions , accomplish the expecting objectives.The innovations of the thesis lie in combining the DNS query , authentication and session initiation into a transaction to finish ,which originally need several transactions to finish. It improve the efficiency effectively , simplify the session flow. In addition , it brings forward the method to the concurrent transactions 's cooperative process ,solve the underlying conflication problems.