03-12-2012, 12:31 PM
Peer-to-Peer Technology
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Abstract:
A peer-to-peer (abbreviated to P2P) computer network is one in which each computer in the network can act as a client or server for the other computers in the network, allowing shared access to various resources such as files, peripherals, and sensors without the need for a central server. P2P networks can be set up within the home, a business, or over the Internet. Each network type requires all computers in the network to use the same or a compatible program to connect to each other and access files and other resources found on the other computer. P2P networks can be used for sharing content such as audio, video, data, or anything in digital format.P2P is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged participants in the application. Each computer in the network is referred to as a node. The owner of each computer on a P2P network would set aside a portion of its resources - such as processing power, disk storage, or network bandwidth - to be made directly available to other network participant, without the need for central coordination by servers or stable hosts.[1] With this model, peers are both suppliers and consumers of resources, in contrast to the traditional client–server model where only the server supply (send), and clients consume (receive).
Introduction:
Peer-to-peer systems often implement an abstract overlay network, built at Application Layer, on top of the native or physical network topology. Such overlays are used for indexing and peer discovery and make the P2P system independent from the physical network topology. Content is typically exchanged directly over the underlying Internet Protocol (IP) network. Anonymous peer-to-peer systems are an exception, and implement extra routing layers to obscure the identity of the source or destination user/node. A pure P2P network does not have the notion of clients or servers but only equal peer nodes 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 of a file transfer that does not use the P2P model is the File Transfer Protocol (FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.
The P2P overlay network consists of all the participating peers as network nodes. There are links between any two nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the overlay network are linked to each other, we can classify the P2P networks as structured or unstructured.In structured P2P networks, peers are organized following specific criteria and algorithms, which lead to overlays with specific topologies and properties. They typically use distributed hash table (DHT) based indexing, such as in the Chord system (MIT). [4]. Structured P2P systems are appropriate for large-scale implementations due to high scalability and some guarantees on performance (typically approximating O(log N), where N is the number of nodes in the P2P system).Unstructured P2P networks do not impose any structure on the overlay networks. Peers in these networks connect in an ad-hoc fashion based on some loose set of rules.[5] Ideally, unstructured P2P systems would have absolutely no centralized elements/nodes, but in practice there are several types of unstructured systems with various degrees of centralization. Three categories can easily be seen:
Architecture of P2P systems:
Peer-to-peer systems often implement an abstract overlay network, built at Application Layer, on top of the native or physical network topology. Such overlays are used for indexing and peer discovery and make the P2P system independent from the physical network topology. Content is typically exchanged directly over the underlying Internet Protocol (IP) network. Anonymous peer-to-peer systems are an exception, and implement extra routing layers to obscure the identity of the source or destination user/node.A pure P2P network does not have the notion of clients or servers but only equal peer nodes 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 of a file transfer that does not use the P2P model is the File Transfer Protocol (FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.The P2P overlay network consists of all the participating peers as network nodes. There are links between any two nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the overlay network are linked to each other, we can classify the P2P networks as structured or unstructured.
Content delivery
• Many file sharing networks, such as gnutella, G2 and the eDonkey network popularized peer-to-peer technologies. From 2004 on, such networks form the largest contributor of network traffic on the Internet.
• Peer-to-peer content delivery networks (P2P-CDN). See : Giraffic, Kontiki, Ignite, RedSwoosh.
• Peer-to-peer content services, e.g. caches for improved performance such as Correli Caches[18]
• Software publication and distribution (Linux, several games); via file sharing networks.
• Streaming media. P2PTV and PDTP. Applications include TVUPlayer, Joost, CoolStreaming, Cybersky-TV, PPLive, LiveStation, Giraffic and Didiom.
• Spotify uses a peer-to-peer network along with streaming servers to stream music to its desktop music player.
Exchange of physical goods, services, or space
• Peer-to-peer renting web platforms enable people to find and reserve goods, services, or space on the virtual platform, but carry out the actual P2P transaction in the physical world (for example: emailing a local footwear vendor to reserve for you that comfy pair of slippers which you've always had your eyes on, or contacting a neighbor who has listed their weedwacker for rent).
• Bitcoin is a peer-to-peer based digital currency.
• Tradepal is a peer-to-peer marketplace where users list, discover, share and trade unique items with trusted peers.
Networking
• Dalesa a peer-to-peer web cache for LANs (based on IP multicasting).
• Voice Peering Fabric is a peer-to-peer interconnect system for routing VoIP traffic between organizations by utilizing BGP and ENUM technology.
Science
• In bioinformatics, drug candidate identification. The first such program was begun in 2001 the Centre for Computational Drug Discovery at the University of Oxford in cooperation with the National Foundation for Cancer Research. There are now several similar programs running under the United Devices Cancer Research Project.
• The sciencenet P2P search engine.
Search
• Distributed search engine, a search engine where there is no central server
• YaCy, a free distributed search engine, built on principles of peer-to-peer networks.
• FAROO, a Peer-to-peer Web search engine
Communications networks
• Skype, one of the most widely used internet phone applications is using P2P technology.
• VoIP (using application layer protocols such as SIP)
• Instant messaging and online chat
• Completely decentralized networks of peers: Usenet (1979) and WWIVnet (1987).