Analyzing BitTorrent and related peer-to-peer networks

Abstract

We analyze protocols for disseminating a collection of data blocks over a network of peers with a view towards Bit-Torrent 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 demonstrate several routing algorithms that distribute b data blocks on a network with diameter d and maximum degree D in O(D(b + d)) phases of concurrent downloads with high probability. This is tight within a factor of D. We also specialize to the networks used by BitTorrent and we improve this bound to O(b ln n) phases where n is the number of clients. Finally, we discuss several practical extensions to BitTorrent, one of which improves the bound to a near-optimal O (b + (ln n)2) phases.