The Design And Implementation Of A SIP Based HD Video Conference System

Nowadays, it is common to take distance learning by video conference. However, the hardware based video conference is too expensive to deploy for distance learning. And as for traditional desktop system, they usually can't offer high quality video & audio service. In most case, they also are not able to support up to more than 1 thousand people online simultaneously in one conference and they cann't run at CNGI based IPv6. So most current hardware based or software based system are not very suitable for distance learning. In this paper, we propose a novel desktop video conference system that provides high quality video service. It can transmit 1080i HD video of the real classroom's situation to the remote student's screen so that make it better for remote student's education effect.The max resolution of video that common commercial video conference can support is 720*576, the real HD video conference is very rare. For the difference between HD video and CIF video is not only its resolution. It brings a lot of problems by HD video transmission such as considerable network bandwidth requirement and high demand of compute capability for both servers and clients to encode, decode and render the HD video. In this paper, we proposethe reliable compound multicast protocol (RCMP) for the mass transmission of real-time data. It is the mixer of IP multicast and over-lay multicast. But it is able to eliminate the drawback of transmission real-time data by over-lay multicast such as uncontrollable delay and hardness of nodes management. And as compare to traditional client/server model, the RCMP can significantly cut the number of required servers in case that there're same clients so that it reduce the deployment cost as well.We take two different methods to solve the packet loss problem brought by the network issue. The first is we use the redundancy codec at application to improve the error tolerance ability. The second is we propose the limited re-transmission of real-time data technique. The combination of these two methods makes it get the quite good result even when the network is not well. It can update its media parameters according to the current network condition by the usage of RTP/RTCP protocol. And it uses the distributed media proxy to solve the feedback exploration problem by overload balance between proxy and server. So, we improve the video & audio quality even when the network condition is poor by the usage of several methods listed above.As for conference control protocol, the system takes the Session Inititation Protocol (SIP) which is the widely used in industry, as thesession control protocol. It expands the ability of SIPX's peer to peer's session to the conference's session according to the RFC Draft for SIP conference. It provides the potential for our system to communicate other systems by usage of SIP.As for network architecture, the system is a distributed video conference and it supports both IPv4 and IPv6 and is equipped with the ability to bypass the NAT/FW. As a result, it provides more flexibility and scalability over traditional system. For example, students can use the IPv4 ADSL to communicate with other clients which are run at CNGI CERNET2 with IPv6.The work in this paper was supported by The State Development and Reform Commission's key research project《CNGI demonstration project---Public Distance Learning system for CNGI》(Project Number: CNGI-04-15-3A)...