Research Of Thenetwork Auto-Adaptability Of Embedded Linux Based Video Conference Products

At present, the global surge in demand for video conference products, especially after the "SARS" incident, in order to ensure security, many large companies carry out business activities through videoconferencing, teleconferencing and web-conferencing. IP is the main form of accessing network for video conference products, while IP networks are "best effort" transmission network. That is, the net try to transmit data as far as possible, but if a problem occurs, the data may be discarded. Therefore, packet loss, out of order, jitter and the resulting outer-sync of audio and video become unavoidable issue in video conference products.After in-depth study on the solutions of these issues at home and abroad, this paper designed a set of adaptive scheme. The implementation of this scheme requires cooperation of the signaling layer and the data layer, so this article first introduced H.323 protocol, which has been regarded as a de facto industry-standard. Chapter II emphasized the adaptive mechanism provides by H.323 system. Then in the third chapter, high-level design of the adaptive scheme TAA was provided. Detailed design and the implementation process of TAA were given in chapter IV. In chapter V, application effects of TAA on embedded Linux-based hardware video conference terminal product has been verified, and the verification results were analyzed and summarized. The final chapter introduced the difficulties encountered during the design and verification process of this paper and how to solve these problems, and the prospect of video conference products in the market and technology trends.This paper first proposed the concept of generalized network adaptive of video conference products. According to this concept, a series of strategies was proposed, including disorder restructuring, jitter cancellation, lost packet retransmission, bitrate self-adaptation, and lip sync strategy. The specific characteristics are shown as below:First, a novel lost packet retransmission strategy with advantages of better performance than single-stage buffer retransmission and simpler realization than multi-stage buffer retransmission is proposed in this paper, which can mostly reduces network burden increase induced by retransmission.Second, a new lip-sync strategy to avoid lip async by transmitting audio and video signals in the same channel is designed in this paper, whose realization needs cooperation of signaling layer and data layer. Third, the bitrate self-adaptation strategy proposed in this paper can mostly alleviate jitters induced by frequency change of bitrate.Fourth, disorder restructuring and de-jitter strategies are commonly used in video conference products and theoretical study on them are mature. The innovation in this paper is based on the optimization and improvement of its way of realization through the buffer queue.In addition, an embedded Linux-based hardware H.323 video conference terminal and a Windows-based software H.323 video conference terminal are realized through a large amount of work on the building of test platform and test methods. Through the communication of the two terminals, application effect of TAA has been verified.Theoretical analysis and experimental results show that the program is a good solution to solve problems of packet loss, disorder, lip async etc. in audio and video transmission of video conference products and significantly improve the quality of the products.