Exploring and improving BitTorrent topologies

BitTorrent, the most popular peer-to-peer (P2P) file-sharing protocol, accounts for a significant fraction of the traffic of the Internet. Using a novel technique, we measure live BitTorrent swarms on the Internet and confirm the conjecture that overlay networks formed by BitTorrent are not locality-aware, i.e., they include many unnecessary long distance connections. Attempts to improve the locality have failed because they require a modification of the existing protocol, or interventions by Internet service providers (ISPs). In contrast, we propose a lightweight method that improves the locality of active swarms by 6% by suggesting geographically close peers with the Peer Exchange Protocol (PEX), without any modifications to the current system. An improvement of locality not only benefits the ISPs by reducing network transit cost, it also reduces the traffic over long-distance connections, which delays the need to expand the infrastructure, easing the power consumption. We expect that if used on a large scale our method reduces the Internet's energy consumption by 8 TWh a year.