The performance and locality tradeoff in bittorrent-like file sharing systems

In recent years, the surge of large-scale peer-to-peer (P2P) applications has brought huge amounts of P2P traffic, which has significantly changed the Internet traffic pattern and increased the traffic-relay cost at the Internet Service Providers (ISPs). To alleviate the stress on networks, methods of localized peer selection have been proposed that advocate neighbor selection within the same network (AS or ISP) to reduce the cross-ISP traffic. Nevertheless, localized peer selection may potentially lead to the downgrade of download speed at the peers, rendering a non-negligible tradeoff between the download performance and traffic localization in the P2P system. Aiming at effective peer selection strategies that achieve any desired Pareto optimum in face of the tradeoff, our contributions in this paper are three-fold: (1) We characterize the performance and locality tradeoff as a multi-objective $b$-matching optimization problem. In particular, we first present a generic weighted $b$-matching model that characterizes the tit-for-tat in BitTorrent-like peer selection. We then introduce multiple optimization objectives into the model, which effectively characterize the performance and locality tradeoff using simultaneous objectives to optimize. (2) We design fully distributed peer selection algorithms that can effectively approximate any desired Pareto optimum of the global multi-objective optimization problem, which represents a desired tradeoff point between performance and locality in the entire system. (3) Taking network dynamics into consideration, we further propose practical protocols that allow each peer to dynamically adjust its peer selection preference on download performance or traffic locality, in order to adapt to the current quality of peering connections, while guaranteeing that the desired tradeoff is still achieved over its entire download process. To support our models and protocols, we have conducted rigorous analysis, extensive simulations, and prototype experiments under various practical settings extracted from real-world traces.