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Issue No. 12 - Dec. (2013 vol. 24)
ISSN: 1045-9219
pp: 2526-2537
Jiaqing Luo , The Hong Kong Polytechnic University, Hong Kong
Bin Xiao , The Hong Kong Polytechnic University, Hong Kong
Kai Bu , The Hong Kong Polytechnic University, Hong Kong
Shijie Zhou , University of Electronic Science and Technology of China, Chengdu
Piece-related algorithms, including piece revelation, selection, and queuing, play a crucial role in the BitTorrent (BT) protocol, because the BT system can be viewed as a market where peers trade their pieces with one another. During the piece exchanging, a peer selects some pieces revealed by neighbors, and queues them up for downloading. In this paper, we provide a deep understanding of these algorithms, and also propose some improvements to them. Previous study has shown that the piece revelation strategy is vulnerable to under-reporting. We provide a game-theoretic analysis for this selfish gaming, and propose a distributed credit method to prevent it. Existing piece selection strategies, though long believed to be good enough, may fail to balance piece supply and demand. We propose a unified strategy to shorten the download time of peers by applying utility theory. The design of the piece queuing algorithm has a conflict with that of piece selection strategy, because it is not possible to assume that the queued requests for a selected piece can always be available on multiple neighbors. We give a possible fix to address the conflict by allowing peers to dynamically manage their unfulfilled requests. To evaluate the performance of the proposed algorithms, we run several experiments in a live swarm. Our primary results show that they can achieve fast individual and system-wide download time.
Protocols, Heuristic algorithms, Games, Algorithm design and analysis, Peer to peer computing, Supply and demand, Degradation

J. Luo, B. Xiao, K. Bu and S. Zhou, "Understanding and Improving Piece-Related Algorithms in the BitTorrent Protocol," in IEEE Transactions on Parallel & Distributed Systems, vol. 24, no. 12, pp. 2526-2537, 2013.
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