Dynamic Peer Grouping Method Conforming with Tit-for-Tat Strategy for P2P File Distribution Systems

Abstract

Some major P2P file distribution systems adopt Tit-For-Tat exchange strategy, which means initially cooperate, then respond in kind to a previous opponent's action, i.e. cooperative or not. However, when sharing a file on such P2P systems, the random peer selection has a problem in that each peer cannot download the file enough efficiently. The peer selection method that groups peers according to their rate has been proposed to solve this problem. This method is supposed to be able to alleviate the difference in performance among peers because it lets peers with similar transmitting rate connect to each other. However, when reduction in peer performance or link one occurs, which is often observed on today's Internet, some problems will emerge, such as it takes a long time for the existing method to reconfigure groups; 2) immediate reconstruction of neighbor peers has not been taken into account when peers detect deterioration in downloading performance. Therefore, we propose a method that reconfigures the group of neighbor peers once a peer notices that the performance of connected peers decreases. The proposed method is evaluated through simulation experiments using BitTorrent as an instance of Tit-For-Tat strategy. The download time of all peers and that of the peer with performance deterioration are estimated focusing on the effect of switching a degraded peer to another immediately. As a result, we confirm that our proposal can distribute files among all peers faster than the existing method keeping incentives for users to some extent. We believe that the proposal which can adapt to the sudden network deterioration is one of the most important technologies for evolution of network software.