Incentivizing Cooperation in P2P File Sharing - Indirect Interaction as an Incentive to Seed

The fundamental problem with P2P networks is that quality of service depends on altruistic resource sharing by participating peers. Many peers freeride on the generosity of others. Current solutions like sharing ratio enforcement and reputation systems are complex, exploitable, inaccurate or unfair at times. The need to design scalable mechanisms that incentivize cooperation is evident. We focus on BitTorrent as the most popular P2P file sharing application and introduce an extension which we refer to as the indirect interaction mechanism (IIM). With IIM BitTorrent peers are able to barter pieces of different files (indirect interaction). We provide novel game theoretical models of BitTorrent and the IIM mechanism and demonstrate through analysis and simulations that IIM improves BitTorrent performance. We conclude that IIM is a practical solution to the fundamental problem of incentivizing cooperation in P2P networks.