FairTorrent: Bringing Fairness to Peer-to-Peer Systems

Proceedings of the 5th ACM Conference on emerging Networking EXperiments and Technologies (CoNEXT 2009), Rome, Italy, December 1-4, 2009, pp. 133-144. (One of the top 3 papers submitted, fast tracked to IEEE/ACM Transactions on Networking)


Peer-to-Peer file-sharing applications suffer from a fundamental problem of unfairness. Free-riders cause slower down load times for others by contributing little or no upload bandwidth while consuming much download bandwidth. Previous attempts to address this fair bandwidth allocation problem suffer from slow peer discovery, inaccurate predictions of neighboring peers’ bandwidth allocations, un derutilization of bandwidth, and complex parameter tuning. We present FairTorrent, a new deficit-based distributed algorithm that accurately rewards peers in accordance with their contribution. A FairTorrent peer simply uploads the next data block to a peer to whom it owes the most data as measured by a deficit counter. FairTorrent is resilient to exploitation by free-riders and strategic peers, is simple to im plement, requires no bandwidth over-allocation, no predic tion of peers’ rates, no centralized control, and no parameter tuning. We implemented FairTorrent in a BitTorrent client without modifications to the BitTorrent protocol, and evaluated its performance against other widely-used BitTorrent clients. Our results show that FairTorrent provides up to two orders of magnitude better fairness, up to five times better download times for contributing peers, and 60% to 100% better performance on average in live BitTorrent swarms.



Columbia University Department of Computer Science