Free-rider Detection and Punishment in BitTorrent Based P2P Networks

BitTorrent is one of the most popular peer to peer (P2P) protocols used for downloading large sized files over internet. Success of BitTorrent relies heavily upon the peers contributing to the protocol by uploading the partially (or fully) downloaded files to other peers. However, it is matter of common observation that very often a peer is found only downloading large files and not allowing uploading of files so as to minimize bandwidth utilization at its own end. Such peers are referred as free-riders and the phenomenon is called free-riding. Free-riding is a major problem in BitTorrent based peer to peer protocol because such free rides consume network resources (download files) without contributing to the network (upload files). In this paper, we first prove empirically that presence of free-riders degrades the performance of BitTorrent system by increasing the download time of peers in P2P networks. Thereafter, a detection-cum-punishment mechanism is proposed which detects and punishes free-riders in P2P network. Impact of proposed mechanism on free-riders and non-free-riders is analyzed using ns-2 based simulation. Results prove that the proposed punishment mechanism improves the performance of the P2P network by decreasing the download times of non-free-rider peers of the network and punishes free-riders by increasing their download times.