Partial Swarm Merger: Increasing BitTorrent content availability

The BitTorrent Peer-to-Peer file sharing protocol is a popular way to distribute digital content. Despite its high scalability and capacity for fast file replication, BitTorrent struggles to replicate rare or unpopular content. Previous work has shown that there is a potential to increase file availability, as there are torrents which share common parts. These arise, e.g., when people publish the same files using different names. This paper presents Partial Swarm Merger (PSM), a novel approach to increase the availability for unpopular content and thus BitTorrent´s performance. PSM exploits the redundancy of content being shared across different swarms. PSM is able to automatically detect torrents with similar content, increasing the number of sources. It does this resorting only to the torrent file info key, which contains hash values for each file part. With PSM, a peer can connect to the several swarms that are sharing files common with the files the peer is downloading. This way, the peer participates in several swarms, announcing and requesting just the common content pieces the original download has with these swarms. Through measurement results, we show that PSM can decrease the download time for all peers and not just the ones using PSM.