Research And Implementation Of Internet Audio/Video Communication Based On SIP

With rapid development and popularity of internet, people have more and more demandsfor internet communication services. Multimedia applications take a leading role in networkcommunication services, in which VoIP(Voice over Internet Protocol) technology isparticularly prominent. VoIP is a kind of IP telephony based on the use of Internet Protocolnetworks for voice transmission and has given birth to several value-added service. Thebiggest advantage of VoIP is that it can make use of the global IP internetworkingenvironment to provide the more and better services than tradition PSTN(Public SwitchedTelephone Network) network.As one of the most important signaling protocol of VoIP technology, SIP(SessionInitiation Protocol) protocol is an application-layer control protocol defined by IETF forcreating, modifying and terminating sessions among two or more parties. Depending on itssimple, opening, flexible, extendable and other characteristics, SIP has become the focus ofmultimedia communication. And it has been adopted by the3GPP(3rd Generation PartnershipProject) for mobile network application protocol, become one of the key technology in thenext generation network technology.Based on RFC3261, this paper offers a thorough research and analysis on SIP protocoland its related extension protocol in this paper. It also gives a brief introduction to the PJSIPopen source that we selected in this paper, and several important modules in PJSIP. On thebasis of understanding the RFC and PJSIP, this paper proposes solutions to improve thesession setup time and stability, the feasibility analysis and measurement results are givenlater.Based on the PJSIP stack, we realize an audio and video communication system in theWindows platform. Its functions include the SIP account registration, audio and videocommunication, status presence, buddy classification and management, etc. The application’smain page shows buddy list, we can operate such functions as deletion, classificationmanagement and making calsl through selected the list of buddy, and add a buddy through thesearch function. In addition, this system also designs the function of SIP signaling of P2P,based on the NAT traversal, the SIP signaling will be sent directly to the remote terminal,instead of through the SIP server forwarding, thus it can reduce the burden of the server andthe network delay caused by packet forwarding of the server.Tests under Windows XP and Windows7operating systems demonstrate that all functionof the SIP communication system works stably, the modification of PJSIP also achieved the expected affect. The system also has good extensibility and we can add more functions to it inthe future.