Study on Multimedia communication systems under heterogeneous network environment

在多媒体通信中，为了避免异质网络环境中的拥塞，需要丢弃低优先级的分组。从这一角度出发，本研究对媒介优先权的处理进行了研究。此外，还讨论了对这种优先结构的客观评价。本文的主要研究结果如下：对于图像媒体，我们提出了一种新的编码方案，该方案既保持了分层结构，又保持了可逆性。对所提出的编码方案的编码效果进行了研究，说明了所提出的编码方案具有很大的优势。此外，对于有损编码，我们发现了一种新的编码方案，该方案具有更好的编码效率。对于网络控制方案，我们提出了一种新的拥塞检测算法，该算法在很短的时间内检测到拥塞，并与一种新的流量控制方案相结合。并对该算法进行了计算机仿真，验证了算法的性能。在此基础上，我们将这一思想嵌入到ATM的ABR服务类中，作为典型应用，我们还开发了一个使用该算法动态控制MPEG流的Q因子的系统。该系统在实际的B-ISDN系统上也得到了实现。

To avoid congestion in heterongeneous network environment during multimedia communication, it is necessary to discard packets of low priority. From this point of view, the treatment of intermedia priority is treated in this study. Further, the objective evaluation of such a priority structure is also discussed. Our primary result of this study are as follows.For the image media, we developed a novel coding scheme where both the hierarchical strucutre and reversibility are sustained. The coding effiecney of the proposed coding scheme is studied and it is clarified that the proposed shemce has a large advantage. Also, for lossy coding, we found a new conding scheme which has better coding efficiency. In finding them, we utilized the strucutre of sub-band coding.For network control sheme, we developed a new congestion deteciton algorithm where such congestion are detected in very short term, which is mixed with a novel flow control scheme. Computer simulation of this algorithm is also performed and the performance is verified. Further, we imbed this idea into the ABR service class of ATM.As typical application, we also developed a system where Q factor of MPEG streams are dynamically contorlled using this algorithm. This system was also implemented on the real B-ISDN systems.