Peer-to-peer

P2P redirects here. For the telecommunications term PTP, see Point-to-Point.P2P can also stand for Pay-to-play in gaming.

Generational classification of peer-to-peer file sharing networks

Some people describe peer-to-peer file-sharing networks by their 'generation'. In this context, they are referring only to the popular internet-based file-sharing networks, not earlier research - and business-oriented peer-to-peer systems, which pre-date them.

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First generation

The first generation of peer-to-peer file sharing networks had a centralized file list, like Napster. Courts in the United States ruled that whoever controlled this centralized file list containing works whose copyright was being infringed was responsible for any infringement.

Related Topics:
United States - Copyright

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Ultimately, Napster was held liable even if it used the most advanced technology available to identify works copyright holders had asked it to block, because no technology that can identify works with 100% certainty exists or can exist. Napster continues to operate today, but the company has taken a new direction, and is now legally distributing music under a subscription-based model.

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In the centralized peer-to-peer model, a user would send a search to the centralized server of what they were looking for, i.e., song, video, movie. The server then sends back a list of which peers have the data and facilitates the connection and download.

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Second generation

After Napster encountered legal troubles, Justin Frankel of Nullsoft set out to create a network without a central index server, and Gnutella was the result. Unfortunately, the Gnutella model of all nodes being equal quickly died from bottlenecks as the network grew from incoming Napster refugees. FastTrack solved the problem by having some nodes be 'more equal than others'.

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By electing some nodes that had more capacity as indexing nodes, and having lower capacity nodes branching off from them, it allowed for a network that could scale to a much larger size. Gnutella quickly adopted this model, and most current peer-to-peer networks follow this model, as it allows for large and efficient networks without central servers.

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Also included in the second generation are distributed hash tables, which solve the scalability problem by electing various nodes to index certain hashes (which are used to identify files), allowing for fast and efficient searching for any instances of a file on the network. They are not without their own drawbacks; perhaps most significantly, DHTs do not directly support keyword searching (as opposed to exact-match searching).

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Third generation

The third generation of peer-to-peer networks are those that have anonymity features built in. Examples of anonymous networks are Freenet, I2P, GNUnet, Entropy.

Related Topics:
Anonymity - Freenet - I2P - GNUnet - Entropy

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Friend-to-friend networks only allow already known users (a.k.a. "friends") to connect to your computer, then each node can forward requests and files anonymously between its own "friends" nodes; some of these networks are: MUTE / Napshare / ANts P2P / WASTE.

Related Topics:
Friend-to-friend - Node - MUTE - Napshare - ANts P2P - WASTE

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Third generation networks, however, have not reached mass usage for file sharing because of the overhead that anonymity features introduce, multiplying the bandwidth required to send a file with each intermediary used.

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