Odd for Even: A Selfishness Prevention File Swap Scheme for BitTorrent

The current BitTorrent-like file sharing systems suffer from peer selfish behaviors. The uncooperative peers can freeload the compliant peers by various methods. To prevent the selfishness, this paper presents a file swap scheme, also known as Odd for Even (OFE), as an enhancement to the current BitTorrent. With OFE, the file is segmented into odd and even pieces; the peers swap the pieces according to "odd first, even later" rule. To study the performance of OFE against the selfish behaviors, a modeling for the related factors is established. We suggest that by using an appropriate file segmentation policy, the free-riders who don\´t make any contribution will undergo a longer download time; the semi-free-riders who only upload odd pieces, deliberately refuse to provide the even ones to save up half upload volume will not get their burden lessened. The experimental results show that OFE can punish these selfish peers effectively.