We consider live continuous broadcast (such as radio or TV) to which users can join with time-shifting. They can join the broadcast at time t and receive the broadcast of time t - w for some offset parameter w ges 0. The simplest implementation that supports such a feature allocates a dedicated channel for each arrival time t and offset value w. Using such a technique, the server bandwidth quickly becomes a bottleneck. We adapt the stream merging technique to the time-shifting model, which allows us to greatly reduce the required server bandwidth. In addition to the application of distributing popular media, there are many other applications such as distance learning and large Internet events that could benefit from the use of time-shifting

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.

The application of unequal loss protection (ULP) algorithms to motion-compensated video over lossy packet networks is studied. In particular, the focus is on streaming video applications over the Internet. The original ULP framework applies unequal amounts of forward error correction (FEC) to embedded data to provide graceful degradation of quality in the presence of increasing packet loss. The ULP framework is applied to baseline H.263, a non-embedded video compression standard, by investigating re-orderings of the bitstream. The re-ordering process makes the bitstream appear embedded, allowing a receiver to display high quality video even at the high loss rate encountered in wireless transmissions and the current Internet.

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 attempt 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.

We address the problem of designing efficient solutions for media-on-demand in systems that use stream merging. In a stream merging system, the receiving bandwidth of clients is larger than the playback bandwidth and clients can buffer parts of the transmission to be played back later. Intelligent use of these resources allows bandwidth usage to be reduced exponentially over traditional unicast delivery of popular media. We design an off-line algorithm that, in O(n) time, computes an optimal off-line stream merging solution for the case when the time horizon n is known ahead of time. In addition, we describe an on-line delay guaranteed solution that operates without knowledge of the time horizon size, and show that it performs asymptotically close to the optimal off-line algorithm. The on-line algorithm is simpler to implement than previously proposed on-line stream merging algorithms, and empirically performs well when the intensity of client arrivals is high.