Peer to Peer (P2P) Technology- How it works:

Ever wondered how P2P works? This guide will run down most of the major P2P services and how they work. Peer to Peer technology lets people share files over a network on the internet. Most people now use what is known as the second generation of P2P, which is unlike its predecessors like such as Napter, the second generation has no centralized server, making it harder for it to shut down.

How first generation P2P services worked:

A connection is established by a peer finding another peer to connect to. Each peer exchanges active peer and their addresses. When a connection has been established, the user can then search for files. When a search has been submitted, it connects to all nodes on its connection list. The results are then displayed and a connection is made.

How second generation P2P services worked:

Gnutella2: Hubs are used to quickly search for files, eliminating the original "find peer and search" method. Instead, they store a list of files on all the "Leaves" (A peer) that are connected to it, thus dramatically reducing search time. Advantages: Unlike Napster, if a hub crashes, it's network stays alive. Disadvantages: Doesn't make network any more durable than the first generation of P2P. Gnutella2: www.gnutella.com

FastTrack: Programs such as Kazaa and iMesh use the FastTrack protocol. Normal peers connect to a supernode which acts jsut like a hub. Supernodes also connect to other supernodes, allowing search requests to move through the network very quickly. Peers then establish a direct connection to a client after a file has been found. Advantages: Any client can become a supernode. Disadvantages: Corruption of files occur. Clients include: Kazaa (www.kazaa.com), iMesh (www.imesh.com)

BitTorrent: .torrent files are used to store information about the file being shared. Once a torrent file is opened, the client connects to the tracker which tells the client where the file is located and what other peers/seeders there are. BitTorrent works by chunks of small files being transferred (even through multiple connections), while you are downloading. The files are checked for corruption as the download continues. Leechers are people who download and don't upload, and are highly frowned upon on some sites, disallowing them from downloading any further. Advantages: Very fast for popular, new files. Disadvantages: Trackers are unreliable and if it goes down, the file is lost. Clients include: Azureus (www.azureus.com), Shareaza (www.shareaza.com).

EDonkey Network: Edonkey runs on the same principle as first generation P2P, only anybody can become a server. Clients communicate with the server to download files, and random chunks can be downloaded in any order then put together in the end. Advantages: No file corruption, leech penalization. Disadvantages: It can penalize users unfairly. EDonkey: www.edonkey2000.com

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