It’s not that simple: an empirical study on the influence of locality on download speed in BitTorrent

Technology. All rights reserved. No part of this series may be reproduced in any form or by any means without prior written permission of the publisher. Wojciechowski et al. Wp The influence of locality on BitTorrentWp PDS Wp Wp Abstract Traffic localization is currently considered a promising approach to decrease the load of P2P systems on the Internet backbone. A number of solutions that promote P2P-locality have therefore been proposed. However, their evaluation has been largely focused on simulations with limited validation against real-world systems. In this paper we empirically measure the influence of locality on end-user download speed in BitTorrent. For that, we design Proximity Toolbox, a set of tools that uses cached round-trip-time measurements to estimate latency and feed close peers to a regular BitTorrent client. We run experiments from five vantage points in North America, Europe and Asia downloading real content using real-world connectivity. We find that locality influences end-user speed in different ways in different locations: it has no effect in one location, generates significant increase (up to 57.65% for the average) in three out of five, but also leads to speed decrease (up to 37%) in one location. Furthermore, we show that this diversity of effects is masked if one overlooks the diversity of vantage points: analyzing all locations together, one can observe a significant positive influence of locality on download speed. Our measurements reveal a more complex picture of P2P-locality than the one considered in the design and evaluation of previous locality-based solutions. Even with few measurement points, we are able to contradict the claim that P2P-locality does not lower end-user performance. This, in turn, points to the need for further research on the factors determining the effectiveness of locality.