Study On VoIP System Based On SIP

With the development of IP technology, which transfer in the IP internet not only was simple data, but also the audio and video media. To support the media operation and supply the function such as call building and session control,the signal protocol is absolutely necessarily. The ITU-T has established the H.323 protocol to build the media conference system, and witch was widely applied in the operation of IP telephone operation. But the H.323 propose succeeded much idea of traditional telephone network, the protocol was complex and its realization was difficult, so it can't completely adapt the requirement of transmitting media in the internet environment. This thesis is study another protocol SIP proposed by IETF in this background.SIP is a signal control protocol on application layer. It uses the C/S pattern which is popular in internet; its message is expressed by text, simple and easy to realize; it has a good expansibility to support developing all kinds of increment operation. So the SIP is focused attention upon and it becomes perfect gradually.This paper studies the function and specialty of SIP,and compares the SIP and H .323. The next,this paper deeply discusses the reliability and expansibility and security of SIP. At last it describes the realization process of SIP servers. Besides, this paper describes NAT Variations and achieves NAT traversal by methods of STUN and Tunnel.