Stream merging is a technique for efficiently delivering popular media-on-demand using multicast and client buffers. Recently, several algorithms for stream merging have been proposed, and in this paper we perform a comprehensive comparison of these algorithms. We present the differences in philosophy and mechanics among the various algorithms and illustrate the tradeoffs between their system complexity and performance. We measure performance in total, maximum, and time-varying server bandwidth usage under different assumptions for the client request patterns. We also consider the effects on clients when the server has limited bandwidth. The result of this study is a deeper understanding of the system complexity and performance tradeoffs for the various algorithms.

Many secure group communication systems rely on a group key, which is a secret shared among the members of the group. Secure messages are sent to the group by encrypting them with the group key. Because group membership is dynamic, it becomes necessary to change the group key in an efficient and secure fashion when members join or leave the group. We present a series of algorithms for solving this problem based on 2-3 trees, where each internal node has degree 2 or 3. The algorithms a t t e m p t to minimize the worst case communication cost of updating the group key and the auxiliary keys needed by the algorithms. The algorithms are analyzed for the worst case performance and evaluated empirically via simulations. We focus on the trade-off between the communication cost due to the structure of the tree and that due to the restructuring of the tree to maintain its structure.

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We study the application of unequal loss protection (ULP) algorithms to motion-compensated video over lossy packet networks. In particular, we focus on streaming video applications over the Internet. The original ULP framework applies unequal amounts of forward error correction to embedded data to provide graceful degradation of quality in the presence of increasing packet loss. In this letter, we apply the ULP framework to baseline H.263, a video compression standard that targets low bit rates, by investigating reorderings of the bitstream to make it embedded. The reordering process allows a receiver to display quality video, even at the loss rates encountered in wireless transmissions and the current Internet.