Reducing Source Load in BitTorrent

One of the main goals of BitTorrent is to reduce load on Web servers by encouraging clients to share content between themselves. However, BitTorrent´s current design relies heavily on the original source to serve a disproportionate amount of the file. We modify standard BitTorrent software so that a source determines the current popularity of each of the blocks of a file and tries to serve only those blocks that are rare. Using extensive PlanetLab experiments, we show that this modification can save a significant amount of the source´s upload bandwidth, with the tradeoff of some increased peer download time. In addition, there are individual experiments that both save bandwidth and have a faster download time than standard BitTorrent. We examine some of the more exceptional experiments, explore alternative algorithms, and provide insight for further improvements.