Streaming audio and video applications are becoming increasingly popular on the Internet, and the lack of effective congestion control in such applications is now a cause for significant concern. The problem is one of adapting the compression without requiring video-servers to re-encode the data, and fitting the resulting stream into the rapidly varying available bandwidth. At the same time, rapid fluctuations in quality will be disturbing to the users and should be avoided.In this paper we present a mechanism for using layered video in the context of unicast congestion control. This quality adaptation mechanism adds and drops layers of the video stream to perform long-term coarse-grain adaptation, while using a TCP-friendly congestion control mechanism to react to congestion on very short timescales. The mismatches between the two timescales are absorbed using buffering at the receiver. We present an efficient-scheme for the distribution of buffering among the active layers. Our scheme allows the server to trade short-term improvement for long-term smoothing of quality. We discuss the issues involved in implementing and tuning such a mechanism, and present our simulation results.
Characterizing the properties of peer-to-peer (P2P) overlay topologies in file-sharing applications is essential for understanding their impact on the network, identifying their performance bottlenecks in practice, and evaluating their performance via simulation. Such characterization requires accurate snapshots of the overlay topology which is difficult to capture due to the large size and dynamic nature. Previous studies characterizing overlay topologies not only are outdated but also rely on partial or potentially distorted snapshots. In this extended abstract, we briefly present the first characterization of two-tier Gnutella topologies based on recent and accurate snapshots.
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