How efficient is BitTorrent?

Abstract

<i>BitTorrent</i> is arguably the most popular media file distribution protocol used in Internet today. Even though empirically <i>BitTorrent</i> seems to be both efficient and scalable, there has been very little research on the detailed dynamics of its built-in control mechanisms, and their effectiveness across a wide variety of network configurations and protocol parameters. The main goal of this paper is to answer the question of how close <i>BitTorrent</i> is to the optimum, and indirectly how much room there is for further performance optimizations. We develop a centrally scheduled file distribution (CSFD) protocol that can provably minimize the total elapsed time of a one-sender-multiple-receiver file distribution task, and perform a comprehensive comparison between <i>BitTorrent</i> with <i>CSFD</i>. In addition, we compare several peer selection algorithms and analyze the applicability of <i>BitTorrent</i> to real-time streaming applications.