CS 186 Lecture 3 — P 2 P File - Sharing

For many applications that require the distribution of files to a very large number of users, peer-to-peer (P2P) file-sharing networks are an attractive alternative to server-based solutions. If the community of file-sharers cooperates appropriately, very high download rates can be achieved at virtually no cost to the injector of the content. We begin this chapter with a brief history of P2P file-sharing, including the rise and fall of Gnutella, and explain why so many file-sharing networks suffer from free riding. We then focus primarily on BitTorrent, the most successful filesharing network to date, with more than 100 Million users worldwide. We describe the BitTorrent protocol in detail, and present some game-theoretic analyses. Finally, we describe multiple attacks on BitTorrent that increase an individual user’s performance, and show how the BitTorrent protocol could be improved to increase overall social welfare.