Bandwidth trading in BitTorrent-like P2P networks for content distribution

Bandwidth trading schemes give peers an incentive to provide upload bandwidth to other peers in a P2P network for fast file distribution. A popular example is the tit-for-tat strategy used in the BitTorrent protocol. Although this game theoretical scheme provides an incentive to peers to contribute resources to the network it does not prevent unfairness and the performances of peers vary considerably. Therefore, we propose two new trading schemes, which are based on pricing. One uses explicit price information whereas the other scheme uses the download rates from other peers as the price. For both distributed algorithms the stable point provides a fair resource allocation as well as a Nash equilibrium. Thus, fairness is preserved although peers behave selfishly and try to maximize their own download rates only. We compare both pricing schemes with BitTorrent in simulations of static and dynamic networks. In BitTorrent peers receive different download rates even if they provide the same upload bandwidth. Furthermore, peers with small upload capacities compared to others receive considerably more than what they, contribute. The pricing algorithms, outperform BitTorrent with respect to fairness. With both algorithms a peer receives a download performance proportional to its upload capacity. With explicit prices the download rates converge faster to the fair equilibrium than with implicit ones. (C) 2007 Elsevier B.V. All rights reserved.