![P2P network](https://upload.wikimedia.org/wikipedia/commons/9/9e/P2P_network.svg)
Peer-to-peer (P2P) computing or networking is a
distributed application
A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer sci ...
architecture that partitions tasks or workloads between peers. Peers are equally privileged,
equipotent
In mathematics, two sets or classes ''A'' and ''B'' are equinumerous if there exists a one-to-one correspondence (or bijection) between them, that is, if there exists a function from ''A'' to ''B'' such that for every element ''y'' of ''B'', the ...
participants in the network. They are said to form a peer-to-peer network of
nodes
In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex).
Node may refer to:
In mathematics
*Vertex (graph theory), a vertex in a mathematical graph
*Vertex (geometry), a point where two ...
.
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. Peers are both suppliers and consumers of resources, in contrast to the traditional
client–server model
The client–server model is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients. Often clients and servers communicate over ...
in which the consumption and supply of resources are divided.
While P2P systems had previously been used in many application domains,
the architecture was popularized by the file sharing system
Napster
Napster was a peer-to-peer file sharing application. It originally launched on June 1, 1999, with an emphasis on digital audio file distribution. Audio songs shared on the service were typically encoded in the MP3 format. It was founded by Shawn ...
, 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
Egalitarianism (), or equalitarianism, is a school of thought within political philosophy that builds from the concept of social equality, prioritizing it for all people. Egalitarian doctrines are generally characterized by the idea that all hum ...
social network
A social network is a social structure made up of a set of social actors (such as individuals or organizations), sets of dyadic ties, and other social interactions between actors. The social network perspective provides a set of methods for an ...
ing that has emerged throughout society, enabled by
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
technologies in general.
Historical development
![SETI@home Multi-Beam screensaver](https://upload.wikimedia.org/wikipedia/commons/b/b4/SETI%40home_Multi-Beam_screensaver.png)
While P2P systems had previously been used in many application domains,
the concept was popularized by
file sharing
File sharing is the practice of distributing or providing access to digital media, such as computer programs, multimedia (audio, images and video), documents or electronic books. Common methods of storage, transmission and dispersion include r ...
systems such as the music-sharing application
Napster
Napster was a peer-to-peer file sharing application. It originally launched on June 1, 1999, with an emphasis on digital audio file distribution. Audio songs shared on the service were typically encoded in the MP3 format. It was founded by Shawn ...
(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."
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
A Request for Comments (RFC) is a publication in a series from the principal technical development and standards-setting bodies for the Internet, most prominently the Internet Engineering Task Force (IETF). An RFC is authored by individuals or g ...
, RFC 1.
Tim Berners-Lee
Sir Timothy John Berners-Lee (born 8 June 1955), also known as TimBL, is an English computer scientist best known as the inventor of the World Wide Web. He is a Professorial Fellow of Computer Science at the University of Oxford and a profess ...
's vision for the
World Wide Web
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web se ...
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 the 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
Broadcasting is the distribution (business), distribution of sound, audio or video content to a dispersed audience via any electronic medium (communication), mass communications medium, but typically one using the electromagnetic spectrum (radio ...
-like structure of the web as it has developed over the years.
As a precursor to the Internet,
ARPANET
The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...
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' address-based routing."
Therefore,
Usenet
Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it was ...
, a distributed messaging system that is often described as an early peer-to-peer architecture, was established. It was developed in 1979 as 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 server
A news server is a collection of software used to handle Usenet articles. It may also refer to a computer itself which is primarily or solely used for handling Usenet. Access to Usenet is only available through news server providers.
Articles and ...
s communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to
SMTP
The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typical ...
email in the sense that the core email-relaying network of
mail transfer agent
The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...
s has a peer-to-peer character, while the periphery of
Email client
An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email.
A web application which provides message management, composition, and reception functio ...
s and their direct connections is strictly a client-server relationship.
In May 1999, with millions more people on the Internet,
Shawn Fanning
Shawn Fanning (born November 22, 1980) is an American computer programmer, entrepreneur, and angel investor. He developed Napster, one of the first popular peer-to-peer ("P2P") file sharing platforms, in 1999. The popularity of Napster was widespr ...
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."
Architecture
A peer-to-peer network is designed around the notion of equal ''
peer'' nodes simultaneously functioning 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 uses the client-server model is the
File Transfer Protocol
The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...
(FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.
Routing and resource discovery
Peer-to-peer networks generally implement some form of virtual
overlay network
An overlay network is a computer network that is layered on top of another network.
Structure
Nodes in the overlay network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through m ...
on top of the physical network topology, where the nodes in the overlay form a
subset
In mathematics, Set (mathematics), set ''A'' is a subset of a set ''B'' if all Element (mathematics), elements of ''A'' are also elements of ''B''; ''B'' is then a superset of ''A''. It is possible for ''A'' and ''B'' to be equal; if they are ...
of the nodes in the physical network. Data is still exchanged directly over the underlying
TCP/IP
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
network, but at the
application layer
An application layer is an abstraction layer that specifies the shared communications protocols and Interface (computing), interface methods used by Host (network), hosts in a communications network. An ''application layer'' abstraction is speci ...
peers are able to communicate with each other directly, via the logical overlay links (each of which corresponds to a path through the underlying physical network). Overlays are used for indexing and peer discovery, and make the P2P system independent from the physical network topology. Based on how the nodes are linked to each other within the overlay network, and how resources are indexed and located, we can classify networks as ''unstructured'' or ''structured'' (or as a hybrid between the two).
Unstructured networks
![Unstructured peer-to-peer network diagram](https://upload.wikimedia.org/wikipedia/commons/f/fa/Unstructured_peer-to-peer_network_diagram.png)
''Unstructured peer-to-peer networks'' do not impose a particular structure on the overlay network by design, but rather are formed by nodes that randomly form connections to each other. (
Gnutella
Gnutella is a peer-to-peer network protocol. Founded in 2000, it was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model.
In June 2005, Gnutella's population was 1.81 million computer ...
,
Gossip
Gossip is idle talk or rumour, especially about the personal or private affairs of others; the act is also known as dishing or tattling.
Gossip is a topic of research in evolutionary psychology, which has found gossip to be an important means ...
, and
Kazaa are examples of unstructured P2P protocols).
Because there is no structure globally imposed upon them, unstructured networks are easy to build and allow for localized optimizations to different regions of the overlay. Also, because the role of all peers in the network is the same, unstructured networks are highly robust in the face of high rates of "churn"—that is, when large numbers of peers are frequently joining and leaving the network.
However, the primary limitations of unstructured networks also arise from this lack of structure. In particular, when a peer wants to find a desired piece of data in the network, the search query must be flooded through the network to find as many peers as possible that share the data. Flooding causes a very high amount of signaling traffic in the network, uses more
CPU/memory (by requiring every peer to process all search queries), and does not ensure that search queries will always be resolved. Furthermore, since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that search will be successful.
Structured networks
![Structured (DHT) peer-to-peer network diagram](https://upload.wikimedia.org/wikipedia/commons/7/79/Structured_%28DHT%29_peer-to-peer_network_diagram.png)
In ''structured peer-to-peer networks'' the overlay is organized into a specific topology, and the protocol ensures that any node can efficiently search the network for a file/resource, even if the resource is extremely rare.
The most common type of structured P2P networks implement a
distributed hash table
A distributed hash table (DHT) is a distributed system that provides a lookup service similar to a hash table: key–value pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key. The m ...
(DHT), in which a variant of
consistent hashing
In computer science, consistent hashing is a special kind of hashing technique such that when a hash table is resized, only n/m keys need to be remapped on average where n is the number of keys and m is the number of slots. In contrast, in most tra ...
is used to assign ownership of each file to a particular peer.
This enables peers to search for resources on the network using a
hash table
In computing, a hash table, also known as hash map, is a data structure that implements an associative array or dictionary. It is an abstract data type that maps keys to values. A hash table uses a hash function to compute an ''index'', als ...
: that is, (''key'', ''value'') pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key.
![DHT en](https://upload.wikimedia.org/wikipedia/commons/9/98/DHT_en.svg)
However, in order to route traffic efficiently through the network, nodes in a structured overlay must maintain lists of neighbors that satisfy specific criteria. This makes them less robust in networks with a high rate of ''churn'' (i.e. with large numbers of nodes frequently joining and leaving the network).
More recent evaluation of P2P resource discovery solutions under real workloads have pointed out several issues in DHT-based solutions such as high cost of advertising/discovering resources and static and dynamic load imbalance.
Notable distributed networks that use DHTs include
Tixati
Tixati is a proprietary Linux and Windows BitTorrent client written in C++. It has standalone and portable versions with each new client version.
Features
In addition to standard BitTorrent client-sharing functions, Tixati provides integral ...
, an alternative to
BitTorrent's distributed tracker, the
Kad network
The Kad network is a peer-to-peer (P2P) network which implements the Kademlia P2P overlay protocol. The majority of users on the Kad Network are also connected to servers on the eDonkey network, and Kad Network clients typically query known nodes ...
, the
Storm botnet, and the
YaCy
''YaCy'' (pronounced “ya see”) is a free distributed search engine, built on the principles of peer-to-peer (P2P) networks created by Michael Christen in 2003. The engine is written in Java and distributed on several hundred computers, , so- ...
. Some prominent research projects include the
Chord project
In computing, Chord is a protocol and algorithm for a peer-to-peer distributed hash table. A distributed hash table stores associative array, key-value pairs by assigning keys to different computers (known as "nodes"); a node will store the values ...
,
Kademlia
Kademlia is a distributed hash table for decentralized peer-to-peer computer networks designed by Petar Maymounkov and David Mazières in 2002. It specifies the structure of the network and the exchange of information through node lookups. Kademli ...
,
PAST storage utility
PAST is a large-scale, distributed, persistent storage system based on the Pastry peer-to-peer
Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are e ...
,
P-Grid In distributed data storage, a P-Grid is a self-organizing structured peer-to-peer system, which can accommodate arbitrary key distributions (and hence support lexicographic key ordering and range queries), still providing storage load-balancing and ...
, a self-organized and emerging overlay network, and
CoopNet content distribution system
Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network. They are said to form a peer-to-peer n ...
. DHT-based networks have also been widely utilized for accomplishing efficient resource discovery for
grid computing
Grid computing is the use of widely distributed computer resources to reach a common goal. A computing grid can be thought of as a distributed system with non-interactive workloads that involve many files. Grid computing is distinguished from co ...
systems, as it aids in resource management and scheduling of applications.
Hybrid models
Hybrid models are a combination of peer-to-peer and client–server models. A common hybrid model is to have a central server that helps peers find each other.
Spotify
Spotify (; ) is a proprietary Swedish audio streaming and media services provider founded on 23 April 2006 by Daniel Ek and Martin Lorentzon. It is one of the largest music streaming service providers, with over 456 million monthly active us ...
was an example of a hybrid model
ntil 2014 There are a variety of hybrid models, all of which make trade-offs between the centralized functionality provided by a structured server/client network and the node equality afforded by the pure peer-to-peer unstructured networks. Currently, hybrid models have better performance than either pure unstructured networks or pure structured networks because certain functions, such as searching, do require a centralized functionality but benefit from the decentralized aggregation of nodes provided by unstructured networks.
CoopNet content distribution system
CoopNet (Cooperative Networking) was a proposed system for off-loading serving to peers who have recently
download
In computer networks, download means to ''receive'' data from a remote system, typically a server such as a web server, an FTP server, an email server, or other similar system. This contrasts with uploading, where data is ''sent to'' a remote s ...
ed content, proposed by computer scientists Venkata N. Padmanabhan and Kunwadee Sripanidkulchai, working at
Microsoft Research
Microsoft Research (MSR) is the research subsidiary of Microsoft. It was created in 1991 by Richard Rashid, Bill Gates and Nathan Myhrvold with the intent to advance state-of-the-art computing and solve difficult world problems through technologi ...
and
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
. When a
server
Server may refer to:
Computing
*Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients
Role
* Waiting staff, those who work at a restaurant or a bar attending customers and su ...
experiences an increase in load it redirects incoming peers to other peers who have agreed to
mirror
A mirror or looking glass is an object that Reflection (physics), reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the ...
the content, thus off-loading balance from the server. All of the information is retained at the server. This system makes use of the fact that the bottle-neck is most likely in the outgoing bandwidth than the
CPU, hence its server-centric design. It assigns peers to other peers who are 'close in
IP' to its neighbors
ame prefix rangein an attempt to use locality. If multiple peers are found with the same
file
File or filing may refer to:
Mechanical tools and processes
* File (tool), a tool used to ''remove'' fine amounts of material from a workpiece
**Filing (metalworking), a material removal process in manufacturing
** Nail file, a tool used to gent ...
it designates that the node choose the fastest of its neighbors.
Streaming media
Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content it ...
is transmitted by having clients
cache
Cache, caching, or caché may refer to:
Places United States
* Cache, Idaho, an unincorporated community
* Cache, Illinois, an unincorporated community
* Cache, Oklahoma, a city in Comanche County
* Cache, Utah, Cache County, Utah
* Cache County ...
the previous stream, and then transmit it piece-wise to new nodes.
Security and trust
Peer-to-peer systems pose unique challenges from a
computer security
Computer security, cybersecurity (cyber security), or information technology security (IT security) is the protection of computer systems and networks from attack by malicious actors that may result in unauthorized information disclosure, the ...
perspective.
Like any other form of
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
, P2P applications can contain
vulnerabilities
Vulnerability refers to "the quality or state of being exposed to the possibility of being attacked or harmed, either physically or emotionally."
A window of vulnerability (WOV) is a time frame within which defensive measures are diminished, com ...
. What makes this particularly dangerous for P2P software, however, is that peer-to-peer applications act as servers as well as clients, meaning that they can be more vulnerable to
remote exploits.
Routing attacks
Since each node plays a role in routing traffic through the network, malicious users can perform a variety of "routing attacks", or
denial of service
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...
attacks. Examples of common routing attacks include "incorrect lookup routing" whereby malicious nodes deliberately forward requests incorrectly or return false results, "incorrect routing updates" where malicious nodes corrupt the routing tables of neighboring nodes by sending them false information, and "incorrect routing network partition" where when new nodes are joining they bootstrap via a malicious node, which places the new node in a partition of the network that is populated by other malicious nodes.
Corrupted data and malware
The prevalence of
malware
Malware (a portmanteau for ''malicious software'') is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, depri ...
varies between different peer-to-peer protocols. Studies analyzing the spread of malware on P2P networks found, for example, that 63% of the answered download requests on the
gnutella
Gnutella is a peer-to-peer network protocol. Founded in 2000, it was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model.
In June 2005, Gnutella's population was 1.81 million computer ...
network contained some form of malware, whereas only 3% of the content on
OpenFT
A gift or a present is an item given to someone without the expectation of payment or anything in return. An item is not a gift if that item is already owned by the one to whom it is given. Although gift-giving might involve an expectation ...
contained malware. In both cases, the top three most common types of malware accounted for the large majority of cases (99% in gnutella, and 65% in OpenFT). Another study analyzing traffic on the
Kazaa network found that 15% of the 500,000 file sample taken were infected by one or more of the 365 different
computer viruses
A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be "infected" with a compu ...
that were tested for.
Corrupted data can also be distributed on P2P networks by modifying files that are already being shared on the network. For example, on the
FastTrack
FastTrack is a peer-to-peer (P2P) protocol that was used by the Kazaa, Grokster, iMesh and Morpheus file sharing programs. FastTrack was the most popular file sharing network in 2003, and used mainly for the exchange of music mp3 files. The netwo ...
network, the
RIAA
The Recording Industry Association of America (RIAA) is a trade organization that represents the music recording industry in the United States. Its members consist of record labels and distributors that the RIAA says "create, manufacture, and/o ...
managed to introduce faked chunks into downloads and downloaded files (mostly
MP3
MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Origin ...
files). Files infected with the RIAA virus were unusable afterwards and contained malicious code. The RIAA is also known to have uploaded fake music and movies to P2P networks in order to deter illegal file sharing. Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern
hashing
Hash, hashes, hash mark, or hashing may refer to:
Substances
* Hash (food), a coarse mixture of ingredients
* Hash, a nickname for hashish, a cannabis product
Hash mark
* Hash mark (sports), a marking on hockey rinks and gridiron football fiel ...
,
chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts.
Resilient and scalable computer networks
The decentralized nature of P2P networks increases robustness because it removes the
single point of failure
A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working. SPOFs are undesirable in any system with a goal of high availability or reliability, be it a business practice, software appl ...
that can be inherent in a client–server based system.
As nodes arrive and demand on the system increases, the total capacity of the system also increases, and the likelihood of failure decreases. If one peer on the network fails to function properly, the whole network is not compromised or damaged. In contrast, in a typical client–server architecture, clients share only their demands with the system, but not their resources. In this case, as more clients join the system, fewer resources are available to serve each client, and if the central server fails, the entire network is taken down.
Distributed storage and search
![Yacy-resultados](https://upload.wikimedia.org/wikipedia/commons/f/f1/Yacy-resultados.png)
There are both advantages and disadvantages in P2P networks related to the topic of data
backup
In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up", w ...
, recovery, and availability. In a centralized network, the system administrators are the only forces controlling the availability of files being shared. If the administrators decide to no longer distribute a file, they simply have to remove it from their servers, and it will no longer be available to users. Along with leaving the users powerless in deciding what is distributed throughout the community, this makes the entire system vulnerable to threats and requests from the government and other large forces. For example,
YouTube
YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...
has been pressured by the
RIAA
The Recording Industry Association of America (RIAA) is a trade organization that represents the music recording industry in the United States. Its members consist of record labels and distributors that the RIAA says "create, manufacture, and/o ...
,
MPAA
The Motion Picture Association (MPA) is an American trade association representing the five major film studios of the United States, as well as the video streaming service Netflix. Founded in 1922 as the Motion Picture Producers and Distribu ...
, and entertainment industry to filter out copyrighted content. Although server-client networks are able to monitor and manage content availability, they can have more stability in the availability of the content they choose to host. A client should not have trouble accessing obscure content that is being shared on a stable centralized network. P2P networks, however, are more unreliable in sharing unpopular files because sharing files in a P2P network requires that at least one node in the network has the requested data, and that node must be able to connect to the node requesting the data. This requirement is occasionally hard to meet because users may delete or stop sharing data at any point.
In this sense, the community of users in a P2P network is completely responsible for deciding what content is available. Unpopular files will eventually disappear and become unavailable as more people stop sharing them. Popular files, however, will be highly and easily distributed. Popular files on a P2P network actually have more stability and availability than files on central networks. In a centralized network, a simple loss of connection between the server and clients is enough to cause a failure, but in P2P networks, the connections between every node must be lost in order to cause a data sharing failure. In a centralized system, the administrators are responsible for all data recovery and backups, while in P2P systems, each node requires its own backup system. Because of the lack of central authority in P2P networks, forces such as the recording industry,
RIAA
The Recording Industry Association of America (RIAA) is a trade organization that represents the music recording industry in the United States. Its members consist of record labels and distributors that the RIAA says "create, manufacture, and/o ...
,
MPAA
The Motion Picture Association (MPA) is an American trade association representing the five major film studios of the United States, as well as the video streaming service Netflix. Founded in 1922 as the Motion Picture Producers and Distribu ...
, and the government are unable to delete or stop the sharing of content on P2P systems.
Applications
Content delivery
In P2P networks, clients both provide and use resources. This means that unlike client–server systems, the content-serving capacity of peer-to-peer networks can actually ''increase'' as more users begin to access the content (especially with protocols such as
Bittorrent that require users to share, refer a performance measurement study). This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor.
File-sharing networks
Many
peer-to-peer file sharing
Peer-to-peer file sharing is the distribution and sharing of digital media using peer-to-peer (P2P) networking technology. P2P file sharing allows users to access media files such as books, music, movies, and games using a P2P software program tha ...
networks, such as
Gnutella
Gnutella is a peer-to-peer network protocol. Founded in 2000, it was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model.
In June 2005, Gnutella's population was 1.81 million computer ...
,
G2, and the
eDonkey network popularized peer-to-peer technologies.
*
Peer-to-peer content delivery networks.
* Peer-to-peer content services, e.g. caches for improved performance such as Correli Caches
* Software publication and distribution (
Linux distribution
A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...
, several games); via
file sharing
File sharing is the practice of distributing or providing access to digital media, such as computer programs, multimedia (audio, images and video), documents or electronic books. Common methods of storage, transmission and dispersion include r ...
networks.
Copyright infringements
Peer-to-peer networking involves data transfer from one user to another without using an intermediate server. Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, over conflicts with
copyright
A copyright is a type of intellectual property that gives its owner the exclusive right to copy, distribute, adapt, display, and perform a creative work, usually for a limited time. The creative work may be in a literary, artistic, education ...
law.
Two major cases are ''
Grokster
Grokster Ltd. was a privately owned software company based in Nevis, West Indies that created the Grokster peer-to-peer file-sharing client in 2001 that used the FastTrack protocol. Grokster Ltd. was rendered extinct in late 2005 by the United St ...
vs RIAA'' and ''
MGM Studios, Inc. v. Grokster, Ltd.
''MGM Studios, Inc. v. Grokster, Ltd.'', 545 U.S. 913 (2005), is a United States Supreme Court decision in which the Court ruled unanimously that the defendants, peer-to-peer file sharing companies Grokster and Streamcast (maker of Morpheus), cou ...
''.
In the last case, the Court unanimously held that defendant peer-to-peer file sharing companies Grokster and Streamcast could be sued for inducing copyright infringement.
Multimedia
* The
P2PTV
P2PTV refers to peer-to-peer (P2P) software applications designed to redistribute video streams in real time on a P2P network; the distributed video streams are typically TV channels from all over the world but may also come from other sources. T ...
and
PDTP protocols.
* Some