peer-to-peer (P2P)

Definition: Learn what peer-to-peer (P2P) means and how the P2P communication model allows each network node to be both a client and a server.

Peer-to-peer is a decentralized communications model in which each party has the same capabilities and either party can initiate a communication session.

Unlike the client/server model, in which the client makes a service request and the server fulfills the request, the P2P model allows each node in a peer-to-peer network to function as both a client and a server. Two computers are considered peers if they are communicating with each other and playing similar roles.

End users in a P2P network must first download and execute a peer-to-peer networking program. After launching the program, the user then enters or selects the address of another computer belonging to the network.  The address, which may look like a screen name or virtual phone number, is actually an IP address. If the sought-after address is connected to the Internet, the end user’s computer will request a connection.

Once a connection has been made, each node can request or send files and messages. Messages on a P2P network can be sent in one of two ways: they may be routed to a specific IP address or they may be broadcast to all nodes on the network. Typically, P2P applications allow users to choose how many member connections to seek at one time and which files can be shared.  Some P2P applications simply connect to any active node in the network and the end user may have no idea whose computer he is connecting to. In this approach, if one connection drops, the application simply opens a new connection with another node on the network in a seamless manner. 

Although uses for the P2P networking topology have been explored since the days of ARPANET, the advantages of the P2P communications model didn’t become readily apparent to the general public until the turn of the century when the use of P2P applications like Napster, Gnutella and BitTorrent began to cut into music and movie industry profits. Since that time, P2P file sharing has become associated with a number of illegal activities in addition to content pirating.  

System administrators tend to discourage the use of P2P applications. In addition to tying up bandwidth, and possibly exposing the administrator’s organization in a legal dispute, P2P applications can be used to bypass firewalls and distribute malware.

See also: Skype protocol, WebRTC, Wi-Fi Direct, P2P botnet


This was first published in August 2014

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