See also: Internet | Network | File sharing | P2P Protocol

Acronym: P2P

Peer-to-peer is a concept whereby one individual directly communicates with another, as opposed to each client referring to a common hub or server. For example, using walkie-talkies is peer-to-peer, while chatting on the phone network as a central hub and is a client-server model.

Table of contents 1 Examples

1.1 Phone System
1.2 IRC

2 Benefits
3 Detractors
4 P2P quotes

4.1 Related Topics


Phone System

One way to illustrate P2P is through the phone system. Phones can be viewed as an system of calls switching between endpoints, similar to the Internet and its packets. Land-line phones behave like the traditional client-server model: they go from location-to-location and users can be fairly confidant where they are phoning but not necesssarily who is going to answer. Meanwhile wireless mobile and cellphones, are like P2P from the user point-of-view; you know who you’re phoning, but not where that person is.


A more direct example of P2P is IRC‘s “DCC Chat” and “DCC Send” tools. These programs only require the network to find other peers. This has several advantages:

  1. Once found, the IRC network can fail and connecting between the two “nodes” will continue.
  2. DCC is faster than normal IRC networks as the server is bypassed in favor of a direct, client-to-client connection.
  3. Communications are more private as the server will not know what or if exchanges are taking place between the two nodes.

Modern Peer-to-Peer systems have more than two individuals and many benefits continue to exist.

Practical implementations are more complex than “P2P” as theory might suggest, often with a mix of centralized hub and peer-connectivity defining the virtual network. Centralized hubs mediate P2P connection and, in some cases, relay all client messages. The faster networks for file sharing have strong hub aspects, or “superpeers” (aka supernodes), who are chosen if they allow fast enough connections.


  • Very robust by sharing bandwidth and files responsibly. Those that wish to get information often also give back to other peers as well. So information of sudden and extreme popularity on a network would not swamp one computer but make it just as available if not more so to all other requests as before its popularity.
  • Improved privacy against eavesdropping by preventing one or a few sources from being primary. Casual observations of Web site preferences such as or may imply sexual or political preference. Because P2P does not work on a web site format, it can make user activity less casually visible. No cookies, no central server like e-mail and is therefore more difficult to track, adding to the number of nodes for possible connection.


  • Devices such as the FBI’s Carnivore and packet sniffing devices do not differentiate between P2P vs. HTTP traffic. To a packet sniffer watching your connection to the Internet, it makes little difference whether you got the phrase “Bush Contra Link” in email or over KaZaA. Some of the tactics used to interfere with one sort of surveillance may even improve other forms; bouncing your search request through 10^3 machines a la Gnutella means that anyone who is watching *ANY* of those 10^3 machines can see the search request; if they want to catch your IP, they’ll respond with a search result for something that looks like what whoever they’re looking for is looking for, just like the spambots do. If your traffic is not encrypted, watching it is trivial.
  • P2P systems are designed for redundancy but only with popular or important files. Unique or low-priority files available on a P2P network might not be present or would be stored on an especially slow node, unlike Web pages who often keep the same content for weeks, months, or even years.
  • Sometimes privacy between peers is not as high. For instance, direct-connections such as IRC’s “DCC Chat” or the AIM Chat Client‘s “Connect to Send IM Image”. However, this can reveal your IP Address, originally hidden by the server. Some P2P systems protect other users from their actual identity and some do not.

Book reference: Peer to Peer: Collaboration and Sharing over the Internet, by Bo Leuf, Addison Wesley 2001, ISBN 0-201-76732-5

P2P quotes

  • “Sharing is caring.”
  • “P2P does not stand for ‘permission to pilfer.'” – US Attorney General under George W. Bush, John Ashcroft
  • “Power to the People.” – Chuck D

Related Topics

TakeDown.NET -> “Peer-to-peer