QoS Research And Implementation Of A Distributed And Software Video-Conferencing

Multimedia, such as stream media, video-conferencing and video on demand, is becoming the important part of information transportation on Internet. The fast development of network, multimedia and micro-electronics provides wider space for network application. And video-conferencing has converted from H.320 system based on ISDN into H.323 system which is based on IP network. Now it is becoming H.332 system based on IP multicast gradually. But point-to-point transmission can't adapt the need of this operation(one point sends, multipoint receives), and it is easy to transmit audio and video of video-conferencing through IP multicast. Correspondingly, it is more difficult for distributed video-conferencing to guarantee the quality of service, such as delay, jitter, lost rate of packets and synchronization of audio and video.We develop a distributed and software video-conferencing for testing use, and give more attention to the key technology, for example, RTP/RTCP, windows sockets and implementation of filters, especially buffer strategy and synchronization. Lastly, we test the system and the result indicates that the performance of the system is satisfactory, not only on LAN, but also onsimulated WAN.We research the quality of service of video-conferencing in-depth and apply it to our system. We resolve the contradiction of delay and jitter better by managing the buffers of audio and video. When the lost rate of the packets is between 2% and 5%, the non-key-frame of video will be discarded to alleviate the congestion of network and to guarantee the fluency of multimedia. When the lost rate of packets ascends unceasingly and the audio becomes worse, the system stops the video transmission to make it work better. As far as the synchronization of audio and video is concerned, the system prints timestamp to multimedia data and adjusts the data buffer to implement it. After testing the system, we find that the system is steady and operated conveniently, what's more, it is easy to expand and can guarantee QoS.