Content availability and bundling in swarming systems

  • Authors:
  • Daniel S. Menasche;Antonio A.A. Rocha;Bin Li;Don Towsley;Arun Venkataramani

  • Affiliations:
  • University of Massachusetts, Amherst, MA, USA;Federal University of Rio de Janeiro, Rio de Janeiro, Brazil;Tsinghua University, Beijing, China;University of Massachusetts, Amherst, USA;University of Massachusetts, Amherst, USA

  • Venue:
  • Proceedings of the 5th international conference on Emerging networking experiments and technologies
  • Year:
  • 2009

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Abstract

BitTorrent, the immensely popular file swarming system, suffers a fundamental problem: unavailability. Although swarming scales well to tolerate flash crowds for popular content, it is less useful for unpopular or rare files as peers arriving after the initial rush find the content unavailable. Our primary contribution is a model to quantify content availability in swarming systems. We use the model to analyze the availability and the performance implications of bundling, a strategy commonly adopted by many BitTorrent publishers today. We find that even a limited amount of bundling exponentially reduces content unavailability. Furthermore, for swarms with highly unavailable publishers, the availability gain of bundling can result in a net improvement in download time, i.e., peers obtain more content in less time. We empirically confirm the model's conclusions through experiments on PlanetLab using the mainline BitTorrent client.