CS 269 I : Incentives in Computer

Ten years ago, the design of peer-to-peer networks was one of the hottest topics in systems research. Less so these days, but peer-to-peer networks remain practically relevant and also provide an intriguing case study of how a system evolves in response to incentive issues. The story begins in 1999, with Napster. The primary purpose of Napster was to provide a centralized and searchable directory listing which users have copies of various files (e.g., mp3s). Prior to this, Internet users exchanged files in a more ad hoc fashion, for example via newsgroups. Napster’s role was that of a match-maker: it matched up people who wanted a file with people who already have it. The file transfer itself was then done directly between the matched users. Note that a user generally acts as a server for some file transfers, and as a client for others (in contrast to the traditional client-server model). In 2000, lawsuits against Napster started rolling in (for copyright infringement). Most famously by the RIAA, but also directly by artists, including Metallica (pissing off all their fans) and Dr. Dre. After Napster failed to comply with requests to block access to copyrighted material, they were shut down in 2001. Napster’s spectacular rise (up to around 25M users) clearly demonstrated the demand for peer-to-peer networks. Its shutdown by the government highlighted the vulnerabilities of a centralized system (like Napster’s directory), so the next step was to develop completely decentralized peer-to-peer networks. In the new systems, each user maintains connections to a group of peers, and searching for a file now involves searching through the network of connections (by breadth-first search, in effect). Once a user with the desired file is located, the file transfer is done directly between the two users. There were several such systems; a major one was Gnutella, which debuted in 2000. The fully decentralized nature of this ∗ c ©2016, Tim Roughgarden. †Department of Computer Science, Stanford University, 474 Gates Building, 353 Serra Mall, Stanford, CA 94305. Email: [email protected]. Others at that time included the now-forgotten FastTrack and eDonkey. Many clever follow-up designs followed throughout the mid-aughts.