The Design And Realization Of SIP Protocol And Its Proxy Server

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 includingvoice, video, and data on the IP network. SIP (Session Initiation Protocol) is just anapplication layer signaling control protocol used to manage the multimedia communication session created on the IP network.SIP is a control stack over application layer. SIP can be used to call, revise, and stop the conversation of the multimedia (or the meeting).Recently, a very obvious change has happened during the development of the NGN. A lot of equipment manufacturer favored SIP stack on the agreement standard of networks, including Cisco, North Telecom who have made greater improvement. SIP has great advantage because of simple, comparing with H.323 standard.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.This is why many Co. select SIP. When IP and multimedia have already become the irreversible trend, SIP is got and pursued is the thing in the reason. At the same time SIP has succession, compared to operator with traditional network, SIP is undoubtedly a breakthrough point forming a connecting link best while the network develops.SIP proxies are located in the middle of the whole SIP architecture. They are mainlyresponsible 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, we apply VC++ 6.0 platform to complete a simple UAC and realize a SIP proxy under Linux OS. By a client, we respectively realize the login/ logout, basic sound test and audio communication between PCand PC.