An introduction to the BitTorrent Peer-to-Peer File-Sharing System
Johan A. Pouwelse, P. Garbacki · 2004
1 IntroductionOver the last few years, quite a few peer-to-peer (P2P) protocols for sharing files(e.g. containing music or movies) have been devised. However, despite the increas-ing attentionfrom both the research communityand hundredsof thousandsof users,the behavior of such systems under a real workload of actual users is poorly under-stood. One of the most promising current P2P file-sharing systems that is quicklygaining popularity, is the BitTorrent/Suprnova system [1]. This paper is an attemptto understand the operation of P2P file sharing by means of detailed measurementsof the use and operation of BitTorrent to assess its quality with respect to such as-pects as download speed and availability. In addition, we propose improvements tothe existing architecture.A high level of robustness and the “one-click download” user interface are impor-tant factors in the success of BitTorrent. BitTorrent is different from other P2Pnetworks in three important respects. First, it does not include a search mechanism,but rather, it relies on central-directory based search facilities as provided by Websites such as suprnova.org, which maintain lists of all files currently availablefor downloading. Secondly, it employs a file-level sharing policy instead of thecommon directory-level sharing policy. Thirdly, it provides a bartering mechanismamong the clients who are downloading the same file, which introduces a certainlevel of fairness into the system.Our focus in this paper is on the usefulness of P2P concepts for the rapid dis-semination of information among large numbers of computers—the fact that also