| With the quick development of the network technology and the appearance of NGN , more and more people want to communicate with each other in multimedia including voice, video, and data on the IP network. SIP (Session Initiation Protocol) is just an application layer signaling control protocol used to manage the multimedia communication session created on the IP network. We can create, modify and terminate a session easily using SIP. If we used SIP with other protocol including RTP, SDP, RADIUS, and combined with other mature system such as DNS and email, we can build a multimedia communication system more quickly and at a very low cost. With SIP, we can easily make our system to support mobility of user, and created new service quickly. SIP proxies are located in the middle of the whole SIP architecture. They are mainly responsible for the routing of SIP message and play a very important role in mobility of user, distribution of function and special policies'deployment. In this thesis, we first introduced the generation, current status, applications and advantages of SIP. Then its basic concepts, architecture and call flows are mentioned. After explaining the SIP transaction, we analyzed the logic construction, running principle of SIP proxy. Finally, based on the analysis of the VOCAL-SIP which is an open source implementation of SIP by VOVIDA, we developed a SIP proxy server and tested it in PC-to-PC VoIP mode by SJPhone. |
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