Interest-Intended Piece Selection in BitTorrent-like peer-to-peer file sharing systems

BitTorrent is a popular peer-to-peer file sharing system and a target file shared through BitTorrent is partitioned into pieces and downloaded from multiple peers in parallel in order to shorten the download process. However, due to peer dynamics in P2P networks, rare pieces may be lost and thus lead to the so-called last piece problem. BitTorrent employs rarest-first piece selection algorithm to deal with this problem, but its efficacy is limited because each peer only has a local view of piece rareness. In this paper, we propose an Interest-Intended Piece Selection (IIPS) algorithm aiming at better alleviating the last piece problem while maintaining stable cooperation between peers. IIPS is named interest intended in that every IIPS peer favors pieces that, if downloaded, would increase the probability of being interesting to its cooperating peers. Simulation results show that IIPS achieves less occurrences of piece loss under tough conditions and slightly outperforms the BitTorrent’s rarest-first algorithm in terms of higher piece diversity.

Research highlights
► We propose Interest-Intended Piece Selection (IIPS) to alleviate the last piece problem in BitTorrent.
► IIPS enlarges a peer’s view to find the more globally rarest pieces.
► By exchanging rare piece vectors, a peer learns other peers’ rare pieces that can be used.
► Transmitting the rare pieces of cooperating peers maintains stable data transmission.
► IIPS enhances system robustness with acceptable message overhead.