Analysing BitTorrent´s Seeding Strategies

BitTorrent is a typical peer-to-peer (P2P) file distribution application that has gained tremendous popularity in recent years. A considerable amount of research exists regarding BitTorrent´s choking algorithm, which has proved to be effective in preventing freeriders. However, the effect of the seeding strategy on the resistance to freeriders in BitTorrent has been largely overlooked. In addition to this, a category of selfish leechers (termed exploiters), who leave the overlay im-mediately after completion, has never been taken into account in previous research. In this paper two popular seeding strategies, the original seeding strategy (OSS) and the time-based seeding strategy (TSS), are chosen and we study, via mathematical models and simulation, their effects on freeriders and exploiters in BitTorrent networks. The mathematical model is verified and we discover that both freeriders and exploiters impact on system performance, despite the seeding strategy that is employed. However, a selfish-leecher´s threshold is identified; once this threshold is exceeded, we find that TSS outperforms OSS - that is, TSS reduces the negative impact of selfish lechers more effectively than OSS. Based on these results we discuss the choice of seeding strategy and speculate as to how more effective BitTorrent-based file distribution applications can be built.