Analyzing the efficiency of bittorrent and related peer-to-peer networks

We analyze protocols for disseminating a collection of data blocks over a network of peers with a view towards BitTorrent and related peer-to-peer networks. Unlike previous work, we accurately model the distribution of the individual data blocks, a process which is critical to the parallelism that makes BitTorrent successful in practice. We also consider multiple network topologies and routing algorithms. We first show several routing algorithms will distribute n data blocks on a network with diameter d and maximum degree D in O(D(d + n)) phases of concurrent downloads with high probability. This is optimal within a factor of D. We also specialize to the networks used by BitTorrent and improve this bound to approximately O(n ln m) phases. Finally, we discuss several practical extensions to BitTorrent, one of which improves this bound to a near optimal O(n + (ln m)) phases.