Collaboration in BitTorrent Systems

Recent research efforts have shown that the popular BitTorrent 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.