Enhancing tit-for-tat for incentive in BitTorrent networks

BitTorrent achives great success in its high performance for file distribution. It is commonly believed that this owes to Tit-for-Tat strategy adopted in choking algorithm for incentive in BitTorrent protocol. But there are still many issues in incentive mechanism in BitTorrent. In this paper, we study Tit-for-Tat strategy by constructing a game model in P2P environments and deducing the constraint under which the strict Tit-for-Tat is an equilibrium strategy. We then enhance and adapt the Tit-for-Tat strategy to the dynamic property in P2P networks, and deduce the constraint under which it is still an equilibrium strategy. We also study through simulations the performance improvement of the enhanced Tit-for-Tat, and give suggestion on how to choose proper system parameters under different network conditions. Finally, based on the enhanced Tit-for-Tat strategy, we propose a method to improve incentive in BitTorrent networks to cope with free-riding and fairness issues.