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Researchers uncover flaw in P2P Wiring

University Of Chicago : 11 October, 2003  (Technical Article)
Few quantitative evaluations of P2P systems have ever been accomplished. 'The decentralized and dynamic nature of a P2P network makes data gathering difficult,' said University of Chicago researcher Matei Ripeanu.
Internet peer-to-peer file-swapping programs that strike fear into the hearts of recording artists and distributors, such as Gnutella and Napster, may not be such terrifyingly efficient instruments of intellectual-property appropriation after all.

An exhaustive study of Gnutella has convinced University of Chicago researchers that Gnutella's architecture does not match the underlying topology of the Internet. They believe Gnutella travels the Web on inefficient wheels -- like a car without snow tires in a blizzard, or a highway-touring bike on a rough mountain trail.

'The way the Internet is wired makes a message going from New York to San Francisco pass through Chicago, for instance,' researcher Matei Ripeanu told NewsFactor. 'The way Gnutella is 'wired', without regard to the underlying Internet, might make a message from New York to San Francisco pass through Tokyo.'

Gnutella nodes, called 'servents' by developers, perform tasks normally associated with both servers and clients, Ripeanu explained. These nodes provide client-side interfaces through which users can issue queries, view search results and accept queries from other nodes.

'The nodes are also responsible for managing the background traffic that spreads the information used to maintain network integrity,' he said.

To become a member of the network, a servent [node] opens one or many TCP (transmission control protocol) connections with nodes that are already in the network. According to Ripeanu, 'Gnutella nodes are computers running Gnutella programs, and virtual links between nodes are open TCP connections between machines.'

Ripeanu's research team, which includes University of Chicago computer science professor Ian Foster and doctoral student Adriana Iamnitchi, programmed a special 'crawler' to join the Gnutella network as a servent and use Gnutella's own protocol to collect topology information. The crawler connected to each node of the network to discover the node's neighbors. 'This way, the crawler incrementally produces a Gnutella map,' explained Ripeanu.

Gnutella's nodes are the primary cause of its inefficient Internet interface. Like notches on the wrong key trying to open a lock, Gnutella's nodes simply do not fit the Internet's 'tumblers.'

'We have performed a number of experiments that confirmed the following intuition: Nodes that are 'close' in the virtual Gnutella topology are generally far apart in the Internet's physical network,' Ripeanu concluded. As a map of the Internet, then, Gnutella is not entirely accurate.

Some experts say the team's findings merely quantify what network engineers have known all along. But few quantitative evaluations of P2P systems have ever been accomplished, Ripeanu pointed out. 'The decentralized and dynamic nature of a P2P network makes data gathering difficult.'

His team studied Gnutella because 'scale, growth rate and its self-organizing, decentralized nature make the Gnutella network interesting,' Ripeanu told NewsFactor. 'Gnutella's open protocol also makes a measurement study possible, and we believe our findings and techniques have broad applicability to P2P systems beyond Gnutella.'

A major implication of the study is that every single user of a P2P program would not have to be shut down to disable the system. Make it annoying enough to obtain content for free, and many consumers will fork over the copyright holder's asking price.

Traffic management innovations may increase Gnutella's efficiency, though, Ripeanu claims. Berklee College of Music professor Peter Alhadeff agrees.

'As P2P networks become ever more popular, open source platforms like Gnutella are the most flexible to incorporate innovations in topographical distribution,' he told NewsFactor. The University of Chicago study 'should promote more knowledge about P2P architecture.'

Ripeanu believes improvements gradually are taking hold in the Gnutella network. 'Today the network is organized in two tiers: Super nodes route most of the traffic, and regular nodes, about 90 percent of all nodes in the network, do not route traffic,' he said. 'Although our study did not directly suggest these improvements, it channeled research efforts by stressing the importance of proper traffic management.'
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