Delay prediction in best effort type network and its application to media synchronization

当在尽力而为型网络中使用一个或多个媒体流时，媒体同步是必要的，以减轻延迟和抖动对应用的影响。从这个角度出发，本研究旨在构建一种新的基于短时延迟过渡及其预测的媒体同步方法。主要结果如下：首先，我们测量了Internet上的短时间端到端时延，发现带有偏移量的指数分布非常符合真实的网络情况。然后，通过详细分析该分布参数的移动，我们证明了没有必要确定参数的过渡时间是没有必要的。因此，在计算机上模拟某个网络时，可以方便地使用该模型。其次，介绍了相位图法测量端到端时延。该方法虽然精度较高，但由于需要离线计算，不能直接应用于媒体同步。因此，我们提出了一种创新的方法，使用相位图的实时性，也提高了性能。在应用方面，本文介绍了一种用于触觉协作系统的媒体同步方法。我们首先做了一个非常密集的实验，阐明了延迟和同步对主观质量的影响。结果与直觉相反，这意味着精确的同步并不总是最好的。换句话说，当存在两个或更多个触觉流时，有时期望尽可能快地激活触觉接口而不等待其他触觉流的信号。考虑到这一点，我们构建了一个合适的触觉流媒体同步机制。

When using one or more media streams in best effort type network, media synchronization is necessary to mitigate the effect of delay and jitter on the applications. From this point of view, this study aimed at constructing a new media synchronization method which is based on the short-term delay transition and its prediction. The major results are the followings.First, we measured the short time end-to-end delay on Internet and found that the exponential distribution with an offset fits the real network case very well. Then, by analyzing the shift of the parameters of this distribution minutely, we showed that it is not necessary to determine the transition time of the parameters is not necessary. Therefore, we can use this model easily when we simulate a certain network on computers.Second, we introduced phase plot method for end-to-end delay measurement. Although this method is rather accurate, it could not be directly applied to media synchronization since it requires some off-line calculation. So, we proposed an innovative method to use phase plot in real-time and also improved the performance. It was also applied to delay prediction and media synchronization.On the application side, we introduced a media synchronization for haptic collaboration systems. We first made a very intensive experiment which clarifies the effect of delay and synchronization on the subjective quality. The result was quite counter intuitive, which means that the precise synchronization is not always the best. In other words, when there are two or more haptic streams, it is sometimes desirable to activate the haptic interface as soon as possible without waiting the signals of other haptic streams. Considering it, we constructed a suitable media synchronization mechanism for haptic streams.