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P2P redirects here. For other uses, see P2P (disambiguation) or Peer-to-peer (disambiguation) . ]] A peer-to-peer (or '''P2P''') computer network is a '' connections. Such networks are useful for many purposes. Sharing content files (see File Sharing ) containing audio, video, data or anything in digital format is very common, and realtime data, such as Telephony traffic, is also passed using P2P technology. A pure peer-to-peer network does not have the notion of clients or servers, but only equal ''peer'' Node s that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the Client-server model where communication is usually to and from a central server. A typical example for a non peer-to-peer file transfer is an FTP server where the client and server programs are quite distinct, and the clients initiate the download/uploads and the servers react to and satisfy these requests. Some networks and channels, such as Napster , OpenNAP , or IRC @find , use a client-server structure for some tasks (e.g., searching) and a peer-to-peer structure for others. Networks such as Gnutella or Freenet use a peer-to-peer structure for all purposes, and are sometimes referred to as true peer-to-peer networks, although Gnutella is greatly facilitated by directory servers that inform peers of the network addresses of other peers. Peer-to-peer architecture embodies one of the key technical concepts of the internet, described in the first internet 1969 . More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing Server s in architectures used for exchanging multimedia files. The concept of peer to peer is increasingly evolving to an expanded usage as the relational dynamic active in distributed networks, i.e. not just computer to computer, but human to human. Yochai Benkler has developed the notion of commons-based peer production to denote collaborative projects such as free software. Associated with peer production are the concept of peer governance (referring to the manner in which peer production projects are managed) and peer property (referring to the new type of licenses which recognize individual authorship but not exclusive property rights, such as the GNU General Public License and the Creative Commons License). OPERATION OF PEER-TO-PEER NETWORKS Three major types of P2P network are: Pure P2P:
Hybrid P2P:
Mixed P2P:
ADVANTAGES OF PEER-TO-PEER NETWORKS An important goal in peer-to-peer networks is that all clients provide resources, including Bandwidth , storage space, and computing power. Thus, as nodes arrive and demand on the system increases, the total capacity of the system also increases. This is not true of a client-server architecture with a fixed set of servers, in which adding more clients could mean slower data transfer for all users. The distributed nature of peer-to-peer networks also increases robustness in case of failures by replicating data over multiple peers, and -- in pure P2P systems -- by enabling peers to find the data without relying on a centralized index server. In the latter case, there is no Single Point Of Failure in the system. When the term peer-to-peer was used to describe the Napster network, it implied that the peer Protocol was important, but, in reality, the great achievement of Napster was the empowerment of the peers (i.e., the fringes of the network) in association with a central index, which made it fast and efficient to locate available content. The peer protocol was just a common way to achieve this. DISADVANTAGES OF PEER-TO-PEER NETWORKS Peer-to-peer networks are limited in size and scope, and they are not designed with security in mind. Each user must take responsibility for the security and management of his or her own machine. Student P2P usage increases the likelihood that violations of copyright laws will occur on university campuses, which exposes a liability that can harm a person or institutions repuation. In addition to issues of legal liability, P2P greatly decreases the bandwidth available on the network. LEGAL CONTROVERSY Under US law, "the Betamax decision" case holds that copying "technologies" are not ''inherently'' illegal, if substantial non-infringing use can be made of them. This decision, predating the widespread use of the Internet applies to most data networks, including peer-to-peer networks, since distribution of correctly licensed files can be performed. These non-infringing uses include sending open source software, public domain files and out of copyright works. Other jurisdictions tend to view the situation in somewhat similar ways. In practice, many, often most, of the files shared on peer-to-peer networks are copies of copyrighted popular music and movies. Sharing of these copies among strangers is illegal in most jurisdictions. This has led many observers, including most media companies and some peer-to-peer advocates, to conclude that the networks themselves pose grave threats to the established distribution model. The research that attempts to measure actual monetary loss has been somewhat equivocal. Whilst on paper the existence of these networks results in large losses, the actual income does not seem to have changed much since these networks started up. Whether the threat is real or not, both the RIAA and the MPAA now spend large amounts of money attempting to lobby lawmakers for the creation of new laws, and some copyright owners pay companies to help legally challenge users engaging in illegal sharing of their material. In spite of the Betamax decision, peer-to-peer networks themselves have been targeted by the representatives of those artists and organizations who license their creative works, including industry trade organizations such as the RIAA and MPAA as a potential threat. The Napster service was shut down by an RIAA lawsuit. In this case, Napster had been deliberately marketed as a way to distribute audio files without permission from the copyright owners. In Grokster the U.S. Supreme Court again held illegal the services of Grokster which included allowing users to illegally share copyrighted music. As actions to defend copyright infringement by media companies expand, the networks have quickly adapted and constantly become both technologically and legally more difficult to dismantle. This has caused the users that are actually breaking the law to become targets, because whilst the underlying technology may be legal, the abuse of it by individuals redistributing content in a copyright infringing way is clearly not. , which also possess anonymizing services, have similar capabilities. In the European Union (EU), the 2001 EU Copyright Directive , which implemented the 1996 WIPO Treaty ("World Intellectual Property Organization Copyright Treaty"), prohibits peer-to-peer, claiming it is a violation of the directive. However, not all European member states have implemented the directive in national legislation. Notably, on December 22, 2005, after discussing the EU directive, the French parliament passed two amendments legalizing the exchange of copies on the internet for private use. In a later proceeding, the French government withdrew the article in question and made illegal any p2p client obviously aimed at sharing copyrighted material. The term "obviously" was not defined. The project of law (called DADVSI ) has still to be discussed by the French senate and, if the decision differs too much from the Parliament's, it will be debated on second lecture back at the Parliament ( Assemblée Nationale ). Important Cases
COMPUTER SCIENCE PERSPECTIVE Technically, a completely pure peer-to-peer application must implement only peering protocols that do not recognize the concepts of "server" and "client". Such ''pure'' peer applications and networks are rare. Most networks and applications described as peer-to-peer actually contain or rely on some non-peer elements, such as ( 1979 ) and FidoNet ( 1984 ). Many P2P systems use stronger peers (super-peers, super-nodes) as servers and client-peers are connected in a star-like fashion to a single super-peer. Sun added classes to the Java technology to speed the development of peer-to-peer applications quickly in the late 1990s so that developers could build decentralized real time chat applets and applications before Instant Messaging networks were popular. This effort is now being continued with the JXTA project. Peer-to-peer systems and applications have attracted a great deal of attention from computer science research; some prominent research projects include the Chord Project , the PAST Storage Utility , the P-Grid , a self-organized and emerging overlay network and the CoopNet Content Distribution System (see below for external links related to these projects). USE OF PEER-TO-PEER NETWORKS IN BIOINFORMATICS Peer-to-peer networks have also begun to attract attention from scientists in other disciplines, especially those that deal with large datasets such as . ATTACKS ON PEER-TO-PEER NETWORKS Many peer-to-peer networks are under constant attack by people with a variety of motives. Examples include:
Most attacks can be defeated or controlled by careful design of the peer-to-peer network and through the use of encryption. P2P network defense is in fact closely related to the " Byzantine Generals Problem ". However, almost any network will fail when the majority of the peers are trying to damage it, and many protocols may be rendered impotent by far fewer numbers. NETWORKS, PROTOCOLS AND APPLICATIONS
An earlier generation of peer-to-peer systems were called "metacomputing" or were classed as "middleware". These include: Legion , Globus , Condor , ByteTornado Multi-network applications SEE ALSO EXTERNAL LINKS REFERENCES |