An Amortized Tit-For-Tat Protocol for Exchanging Bandwidth instead of Content in P2P Networks

Incentives for resource sharing are crucial for the proper operation of P2P networks. The principle of the incentive mechanisms in current content sharing P2P networks such as BitTorrent is to have peers exchange content of mutual interest. As a consequence, a peer can actively participate in the system only if it shares content that is of immediate interest to other peers. In this paper we propose to lift this restriction by using bandwidth rather than content as the resource upon which incentives are based. Bandwidth, in contrast to content, is independent of peer interests and so can be exchanged between any two peers. We present the design of a protocol called amortized tit-for-tat (ATFT) based on the bandwidth-exchange concept. This protocol defines mechanisms for bandwidth exchange corresponding to those in BitTorrent for content exchange, in particular for finding bandwidth borrowers that amortize the bandwidth borrowed in the past with their currently idle bandwidth. In addition to the formally proven incentives for bandwidth contributions, ATFT provides natural solutions to the problems of peer bootstrapping, seeding incentive, peer link asymmetry, and anonymity, which have previously been addressed with much more complex designs. Experiments with a real-world dataset confirm that ATFT is efficient in enforcing bandwidth contributions and results in download performance better than provided by incentive mechanisms based on content exchange.