Enhancing Content Distribution Performance of Locality-Aware BitTorrent Systems

Locality-aware BitTorrent (BT) systems reduce the inter-ISP traffic by providing peers with physically close neighbors. However, they still rely on randomized optimistic unchoking, leaving a design space for performance improvement. In this paper, we propose a biased optimistic unchoking mechanism called PicBou. In PicBou, a typical peer prefers to optimistically unchoke the neighbors that are physically close to it or have file pieces rarely replicated among its internal neighbors. The PicBou enables peers in the same ISPs to cooperatively get missing pieces in a prompt way, and share pieces among internal neighbors once the pieces have been downloaded into the ISPs. This feature greatly reduces the content distribution time and saves the backbone bandwidth consumption. The PicBou is simple and can be easily integrated in current locality-aware BT systems. We evaluate the performance through extensive simulations. The results show that PicBou reduces the content distribution time of locality-aware BT systems by about 20% and cuts down the inter-ISP traffic by 19-36%.