The Research Of Video Conference System Based On SIP Protocol And ALM

Video conference system is now one of the most brisk demand in network video application fields. while conventionally most of them are built based on H.32 X protocol, IETF work group has proposed SIP protocol as a replacement, which is easy to build and flexible to extend.This paper designed a video conference system based on SIP protocol.To have a basic understanding about SIP, this paper first introduced the packet format, network logical unit, and the basic work flow of SIP protocol.SIP needs to cooperate with many other protocols, and this paper also briefly introduced some related protocols such as SDP, RTP and RTCP.This paper compared various topological structures of video conference system in two ways, the control and the media flow, thus getting the conclusion that centralized control flow and multicast media flow have advantage over others. As IP layer multicast is not yet well developed in real network environment, this paper proposed application layer multicast as a replacement. After comparing two node availability calculation models, the way based on node comprehensive ability and the way based on average RTT, this paper combined them as the final calculation model to build application layer multicast tree, and described detailed algorithm of the tree maintenance.On the basis of video conference system requirements, this paper gave a description about the overall system architectures and and functions of all modules.Combined with SIP protocol and application layer multicast tree, this paper discussed the detailed implementation, and showed SIP message communication process. QoS is important for multimedia network applications, this paper made use of RTCP protocol to detect network congestion, put forward the conception of local congestion and overall congestion, and designed congestion solution.In the end, this paper implemented the system based on PJSIP and JRTPLIB library, and test the system to ensure function integrity.