Peer-to-peer, or P2P, networking involves the sharing of files between two PCs that are connected either directly or, as is most common, through a third-party server that acts as a “broker.”
Because P2P increasingly involves exchange of video files such as lengthy movies and TV episodes, it tends to consume a great deal of bandwidth, especially when reaching neighborhood cable drops engineered to divide bandwidth among four to eight homes.
One P2P user in such a group can occupy up to 90 percent of the available bandwidth, resulting in a dramatic decline in quality for the other users.
There are two flavors of P2P. Services such as LimeWire, Gnutella, and KaZaA do not keep any content on their servers. Instead, the servers respond to a user request, say for the latest episode of CSI, by searching a worldwide network of other user PCs registered with the Web site. If the file is popular, the P2P service can draw different parts of the file from numerous PCs simultaneously, accelerating the download time.
The second model allows PC users to upload content to a server where it is stored and remains available to others. This model was pioneered by Napster and ultimately led to the service’s downfall because the courts ruled that it was, in effect, distributing copyrighted material.
This second P2P model, which Comcast targeted, is legal when the author or artist waives electronic distribution rights. Internet enthusiasts point to this model as a way for musicians and filmmakers to bypass conventional industry distribution channels and reach audiences directly.
Pure P2P, in which the service acts as a facilitator and does not copy or distribute content from a central point, occupies a murkier legal area. These sites are under legal attack from the recording and motion picture industries.
— Steven Titch