Peer to Peer File Download and Streaming

Peer-to-Peer file distribution is an attractive alternative to IP multicast for efficient dissemination of large files and media streams from one source to a large number of receivers. Typically, the file being distributed is divided into a number of blocks, which the source sends to different receivers. All the receivers serve both as a sender and as a receiver, and are organized into an overlay mesh. Several P2P file distribution systems have been developed and implemented that use this overlay mesh architecture to maximize the overall data transfer bandwidth. The most influential among them is BitTorrent because it is the first and also the most popular. So far no other peer-to-peer file distribution systems are able to outperform BitTorrent in any significant way. Although empirically BitTorrent seems to be both efficient and scalable, there has been very little research on the detailed dynamics of its built-in control mechanisms, and their effectiveness across a variety of network configurations and protocol parameters. Moreover, it is not known how much room is available for further performance optimization. In this study, we first propose a centrally scheduled file distribution (CSFD) protocol, which can provably minimize the total elapsed time of a one-sender-multiple-receiver file distribution task. Then we develop a discrete-event simulator for the BitTorrent protocol to study the performance impacts of its various design decisions and to compare it with CSFD. Finally, we analyze the suitability of BitTorrent in supporting media streaming applications and suggest necessary modifications.