Collaboration in BitTorrent systems

Abstract

Recent research efforts have shown that the popular Bit-Torrent protocol does not strictly enforce fairness and allows free-riding, mainly via optimistic unchokes. This paper proposes a BitTorrent-like protocol, that encourages peers of similar upload bandwidth to be buddies- peers collaborating for mutual benefit. Buddy peers mostly satisfy their download needs through their buddies and perform optimistic unchokes only when absolutely necessary. As a result, the buddy protocol improves fairness via explicit cooperation between buddies, and limits bandwidth spent on random optimistic unchokes, leading to a system more robust against free-riders. We implemented the buddy protocol on top of an existing BitTorrent implementation and ran experiments on a controlled PlanetLab testbed to evaluate its impact. Our results show that the buddy protocol promotes fairness, discourages free-riding, and improves the robustness of the system as compared to regular BitTorrent. It also provides incentives to be adopted by all the peers in the system. © IFIP International Federation for Information Processing 2009.