Study of MPEG VBR sequence quality transmitted with rt-VBR and ABT/DT contracts

In this paper, we study the impact of resource allocation protocol on the quality of an MPEG sequence encoded in a variable bit rate mode (MPEG VBR). The transmission of the video with real-time constraints will be made through one of the following contracts: constant bit-rate (CBR), real-time variable bit rate (rt-VBR), ATM block transfer (ABT). CBR contract leads either to an under-utilization of resources or a greater end-to-end delay. rt-VBR contract allows statistical multiplexing but induces inevitably cell losses in the network. Fast reservation protocol (FRP) having given birth to the ABT contract is based on a preliminary resource reservation. The reserved bandwidth can be less than the bandwidth requested by the application. We propose a method to estimate the qualify degradation caused by image size reduction. It is shown that the sequence quality is less damaged by reducing image size at the encoder level with the ABT contract than by a random cell loss inside the network with the rt-VBR contract. Finally, we present a novel mechanism for real-time video transmission over ATM networks based on ABT contract.