Date Added: Jan 2010
Incentive mechanisms play a critical role in P2P systems. Private BitTorrent sites use a novel incentive paradigm, where the sites record upload and download amounts of users and require each user to maintain its upload-to-download ratio above a specified threshold. This paper explores in-depth incentives in private P2P file-sharing systems. The contributions are threefold. They first conduct a measurement study on a representative private BitTorrent site, examining how incentives influence user behavior. The measurement study shows that, as compared with public torrents, a private BitTorrent site provides more incentive for users to contribute and seed. Second, they developed a game theoretic model and analytically show that the ratio mechanism indeed provides effective incentives. But existing ratio incentives in private BitTorrent sites are vulnerable to collusions.