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1 This paper defines a retransmission scheme for transmitting video data which allows the use of robust decoding (such as Joint Source and Channel Decoding) jointly with acknowledgement procedures. Conventional video communications use CRC-based retransmissions to obtain a nominal quality of the video (defined by the source coder). A lot of work has also been done on robust video transmission, which aims at providing a video of the best possible quality, for a given channel. However, robust techniques are not compatible with CRC-based retransmissions, and the quality of the received signal cannot really be controlled. As a result, the throughput is the best possible one, at the cost of a reduced quality.The scheme we define allows the use of robust decoding together with retransmissions, thus improving the throughput of the system while trying to keep the nominal quality. As a result, the proposed scheme is compatible with most actual mechanisms. The method is based on an evaluation of the quality of the robust estimate, followed by an hypothesis testing to decide whether a retransmission is necessary or not. Simulations evaluate the quality and the average number of retransmissions.

1 In this paper, we study schemes for efficient multicast scalable video streaming. Multicast streaming is based on the fact that the same video content is conveyed to several users in the same environment. Conventional GBN and SR multicast schemes are extended to the case of two finite streams transmissions. A new scheme is also proposed. The three schemes are compared in terms of performance and buffering requirement. Computer simulations are used to evaluate the performance, while an analytical expression of the new scheme's throughput is derived.