The Design Of Video Conference System Based On SIP

With the increasingly development of internet and communication technology, the traditional point-to-point voice communication couldn't meet people's requirement of more people involved and more interactive media. Especially in commercial business and industrial enterprises, people at anywhere require contact with others using video, characters and other communication modes, except from voice chat. Therefore, the devices such as video conference systems, integrating media information codec, data transferring and controlling, peripherals and so on, cater to this kind of people's requirement.After examining the trends of video conference system designing, it's found that, SIP signaling technique can provide more flexible controlling and more extensible application in the IP-based Internet compared to H.323 protocol, which prompts SIP to become the mainstream choice in session controlling of video conference system. Refer to RFC3261, RFC3265, RFC3550 and other protocols from IETF organization, a video conference system based on SIP was designd. The SIP protocol is adopted as communication signaling, controlling session, as well as RTP protocol is choosed to be media streaming standard. The brief and high-efficient conference management logics, typical flow of SIP signaling in conferencing, speech and video data transmission policy were designed, programmed and implemented.During the procedure of system design and implement, an improved mixing architecture and overflow handling algorithm, which are adapted to the features of the speech signal, is proposed in this thesis. Based on traditional attenuation factor method, the short-term energy and the short-term zero crossing rate of the speech signal is used to dynamically revise the mixing factor in the proposed method. And the experiment results show that the proposed algorithm has favorable hearing comfort and the efficiency mixing performnce. On the basis of the H.264 encode and decode design, by taking advantage of the DM6446 dual core processor, codec engine from TI was applied to improve video processing performance and decrease the load of ARM. And in the H.264 transmission with RTP, a fragmenting and aggregating procedure was designed and implemented for the video data transmitting over network.By building a test environment, the SIP video conferencing system signaling interaction, voice transmission and video transmission have been tested in the LAN environment. It's proved that the video conferencing system is designed well, and the flow of SIP signaling interaction, conference creating, inviting participant, subscribing and conference closing are implemented precisely. And the voice transmission delay is small, the acoustic fidelity is good, video transmission and display is smooth.