Priority statistical multiplexing and two-level congestion control for video transmission over ATM networks.

摘要

This dissertation is divided into three parts: In the first part, we analyze the traffic characteristics generated by the layered Motion Picture Export Group (MPEG) coder wherein block Discrete-Cosine-Transfer (DCT) components are divided into two layers by a cut-off frequency. The layered MPEG video coder produces bursty traffic at both the primary layer and the secondary layer. Since the video signals at the primary layer are crucial to the decoded video quality, we propose a congestion control scheme for the sending traffic at this layer by adapting the cut-off frequency. This process changes the bit distribution between the primary layer and the secondary layer, but not the overall traffic. Therefore, the burstiness of the primary traffic is controlled without affecting overall video quality. We analyze how the scene change event affects the statistical characteristics of video traffic, and exploit the probability of scene change as a traffic parameter to describe the traffic of a video sequence.;In the second part, a priority multiplexing system is designed to support priority video traffic. The space priority mechanism is exploited to manage the multiplexing buffer access.;In our system, each video source produces two priority video streams which are packetized into different ATM cells. Before the cells enter the multiplexing buffer, the traffic is deterministically smoothed in a way that cells are equispaced at the frame level. With this deterministic smoothing scheme, no cells can be lost if aggregate arrival traffic does not exceed channel capacity with a certain buffer constraint. Moreover, the cell loss rate can be determined if the aggregate arrival traffic surpasses the channel capacity. We develop a deterministic partial buffer sharing scheme (DPBS), which can analytically determine the threshold for each loss priority class with given loads. With the DPBS scheme, primary cell loss due to network congestion can be prevented if aggregate primary arrival traffic is enforced not to exceed the channel capacity. The DPBS scheme combined with the primary congestion control scheme constitutes our first-level congestion control to prevent primary cell loss. This multiplexing system is characterized by its high performance and cheap implementation.;In the third part, we propose a novel burst-based congestion control scheme at the second-level which we refer to as the congestion control with burstiness adjusting (CCBA) scheme. In this scheme, burstiness of video traffic is adjusted on the basis of network conditions. Control does not take effect if the current traffic of VBR video does not exceed the burstiness allowed. Higher compression and transmission performance is expected from this scheme. We gain an insight into the cell-inter-arrival process and show that current network conditions can be used to make control decisions. Moreover, we have developed an analytical model to evaluate the performance of our CCBA scheme. Analytical and simulation results show that the CCBA congestion control scheme can significantly reduce cell loss rate without losing network throughput. (Abstract shortened by UMI.).