Design And Implementation Of Multimedia Communication System Based On SIP

Nowadays, Internet had go into all countries in the world, extended every angle. IP is more compatible to data communication comparing with . All kinds of services by Internet poured the energy into for the development of Internet, e.g. IP telephone, VOD, and multimedia conference, they had the wide using prospect. At present, IP telephone signaling had two parts, one is IETF's SIP, the other one is ITU-T's H.323. H.323 is matured as was developed earlier than SIP, so H.323 occupied more market share, but as the technology develops, H.323 can't adapt to the new requirements, and then fitting the new requirements, SIP come out. SIP(Session Initiation Protocol) is proposed by IETF(Intenret Engineering Task Force), used for creating, modifying and terminate a multimedia session included one or more participants. It can syncretize telecommunication and Internet application well, break up the conventional transmission mode, provide Internet service based on Internet rules, has rosy prospects, so SIP is used in multimedia communication by more and more developers. Comparing with H.323, SIP is more flexible, more simple, more extensive, and reuses other matured protocols, and has loose coupling status with other protocols. As SIP is payed close attention by in industry, SIP developed fast. So this article mainly discusses multimedia communication around SIP.This article mainly researched SIP and correlative protocols, includes SIP methods and messages, extension mechanism, security and QoS, SDP, cooperation with other protocols which are ruled by kernel part(RFC3261 and RFC3265), and then designed a multimedia communication system based on SIP. The system has the properties below:1. Server Proxy server, register server, location server.2. Intelligent terminal Windows OS terminal, Linux OS terminal. 3. Signaling SIP, SDP4. Media protocols G.711, G.723,H.261, H.2635. Interface(GUI) MFC framework6. Platform Windows OS, Linux OS, VC++2005, DirectShow, Windows media SDK7. Network environment LAN, four PCsServer was developed by using the OperSER kernel, has the functions of calling forward, called address inquiring, registering terminals. OperSER is GNU open source program, is SIP server based on Linux OS, using Mysql database, open source code, simple and effective. Terminals include Windows terminal and Linxu terminal.Windows terminal using oSIP open source stack, and which was optimized. The developer added MWSSAGE, SUBSCRIBE and NOTIFY methods to suit RFC3261 and RFC3265. The terminal can communication through proxy server, using G.711,G.723 and H.261, H.263 compression algorithm and DirectShow technique to deal with audio and vedio stream. The terminal has friendly interface, implementationed audio and video communication, IM(instant message) service, except for those, and also friend list, group management, presence service, parameter output, and so on.Because of the university of using Windows OS, developing Windows terminal software is valuable. Comparing with other congener products, this Windows terminal named vCOM has the strongpoints below:1. Properitary intellectual property rights At present, other Windows terminals does not open source code, so the research need to build Windows terminals by myself. This is basement.2. Support more methods and message most terminal support the RFC3261, this terminal also support RFC3265 except for RFC3261. 3. Friendly GUI This terminal has friendly GUI comparing with other congener products, includes group management, presence service, nickname setting, response mode and so on.For riching the system and testing the developed Windows terminal by me standard, the multimedia system add the Linux open source terminal named linphone. The system was tested in four PCs based on LAN, the audio and video communication is normal, and has good cooperation with other SIP terminals.