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Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or work loads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes. Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts.〔Rüdiger Schollmeier, ''A Definition of Peer-to-Peer Networking for the Classification of Peer-to-Peer Architectures and Applications'', Proceedings of the First International Conference on Peer-to-Peer Computing, IEEE (2002).〕 Peers are both suppliers and consumers of resources, in contrast to the traditional client-server model in which the consumption and supply of resources is divided. Emerging collaborative P2P systems are going beyond the era of peers doing similar things while sharing resources, and are looking for diverse peers that can bring in unique resources and capabilities to a virtual community thereby empowering it to engage in greater tasks beyond those that can be accomplished by individual peers, yet that are beneficial to all the peers. While P2P systems had previously been used in many application domains,〔D. Barkai, ''Peer-to-Peer Computing'', Intel Press, 2002.〕 the architecture was popularized by the file sharing system Napster, originally released in 1999. The concept has inspired new structures and philosophies in many areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that has emerged throughout society, enabled by Internet technologies in general. ==Historical development== While P2P systems had previously been used in many application domains,〔 the concept was popularized by file sharing systems such as the music-sharing application Napster (originally released in 1999). The peer-to-peer movement allowed millions of Internet users to connect "directly, forming groups and collaborating to become user-created search engines, virtual supercomputers, and filesystems." 〔Oram, A. (Ed.). (2001). Peer-to-peer: Harnessing the Benefits of a Disruptive Technologies. O'Reilly Media, Inc.〕 The basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.〔RFC 1, ''Host Software'', S. Crocker, IETF Working Group (April 7, 1969)〕 Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links. The early Internet was more open than present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures.〔 This contrasts to the broadcasting-like structure of the web as it has developed over the years.〔 Is This "Peer-to-Peer" About? (pp. 9-16). Springer Berlin Heidelberg.〕 As a precursor to the Internet, ARPANET was a successful client-server network where "every participating node could request and serve content." However, ARPANET was not self-organized and it lacked the ability to "provide any means for context or content based routing beyond 'simple' addressed based routing."〔Steinmetz, R., & Wehrle, K. (2005). 2. What Is This "Peer-to-Peer" About? (pp. 9-16). Springer Berlin Heidelberg.〕 Therefore, a distributed messaging system that is often likened as an early peer-to-peer architecture was established: USENET. USENET was developed in 1979 and is a system that enforces a decentralized model of control. The basic model is a client-server model from the user or client perspective that offers a self-organizing approach to newsgroup servers. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email relaying network of Mail transfer agents has a peer-to-peer character, while the periphery of e-mail clients and their direct connections is strictly a client–server relationship. In May 1999, with millions more people on the Internet, Shawn Fanning introduced the music and file-sharing application called Napster.〔 Napster was the beginning of peer-to-peer networks, as we know them today, where "participating users establish a virtual network, entirely independent from the physical network, without having to obey any administrative authorities or restrictions."〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Peer-to-peer」の詳細全文を読む スポンサード リンク
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