Research And Practice On Distributed Videoconference System Based On IP Network

This is a research and practice on distributed videoconference system based on TCP/IP network. The system is distributed mode. Based on the Mbone, the system can make the remote and motive members to join a conference. The system uses multimedia PC as its terminal. The real-time audio and video communication between the terminals is realized by software. There are three sorts terminal in the system: president terminal, speaker terminal and listener terminal. The president terminal is used for controlling. The speaker terminal transmits his information to other terminal by multicast, which can save much network bandwidth. The original audio information is compressed on G.723. I standard. l5kbit/s bandwidth is needed to transmit the compressed audio. Flow control is implement when the compressed video information is transmitted: the transmitted video data is changed based on the real-time network bandwidth. As a result of flow control, the images are refreshing at five speeds: I FIS, 5F/S, 1OFIS, 15FIS and 2OFIS. Different speed need different bandwidth, for example, transmit 384*284 image at 20F/S speed used 1 .6Mbit/s. The RTP/RTCP is realized by software to make transmit real-time video and audio information well. With the help of RTP, synchronization between audio and video is resolved. Instead of MCU, Distributed Videoconference Manager (DVM) is designed to manage and control the conference, which is more suitable in distributed conference. Since each terminal has a DVM, the manage function is easy completed through DVM cooperates with each other. Because the system uses the multicast technology advanced in multimedia communication applications, the present research work has both practical and investigative values.