When dealing with any large network of users, be it social, technical, or some amalgamation of both, a discussion of network externalities will often yield fruitful results. As peer-to-peer filesharing systems are often large in both scope and impact on modern computer users, one might expect that there would be a host of literature discussing the network effects created by users joining peer-to-peer system. However, this seems not to be the case, although there are a few on the subject.

One of the few papers available is An Emperical Analysis of Network Externalities in Peer-To-Peer Music Sharing Networks by Asvanung, Clay, Krishnan, and Smith. This paper analyzes data collect in 2000-2001 from a number of OpenNap peer-to-peer networks of varying sizes in an attempt to determine the network externalities in that type of network, and to use those externalities to predict an optimal size for a filesharing network. The externalities that the paper identifies are both positive and negative. On the one hand, the more users that are logged into a network, the more files exist, and the more redundant those files are, both of which is a benefit to users. However, because the OpenNap protocol uses a central server to catolog available materials, additional users will create congestion for the server, which is a negative effect of a growing user base.

These two things combined won’t neccessarily limit the optimal size of a network. However, the paper hypothesizes that, in fact, the positive effects of additional users decrease with the size of the network, while the negative effects increase. This would eventually lead to a situation where the negative effects of additional users outweighed the positive, and the network would have reached the optimal size. The researchers used several measures of file availability and congestion, and provided evidence that this was indeed occuring.

However, this paper was written in 2002-2003, and peer-to-peer filesharing networks have changed since then. Bittorrent, which uses a decentralized server model, has gained ground, and other network protocols have come into existence. So while the analysis of OpenNap still stands, it would be useful to see an updated estimate of network effects on more modern systems.