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Part of a series on
File sharing
Technologies
Peer to peer BitTorrent File hosting services
Development and societal aspects
Timeline Legal aspects
Non-public file sharing
Anonymous P2P Friend-to-friend Darknet Private P2P
File sharing networks and services
Gnutella / Gnutella2 (G2) FastTrack eDonkey Direct Connect Mininova isoHunt The Pirate Bay ExtraTorrent
By country or region
Canada UK
v t e

Peer-to-peer file sharing (known in internet shorthand as "P2P") allows users to download media files such as music, movies, and games using a P2P software client that searches for other connected computers.^[1] The "peers" are computer systems connected to each other through the Internet. Thus, the only requirements for a computer to join peer-to-peer networks are an Internet connection and P2P software.^[2] The first generation of P2P software is Napster, a central server-based model that was eventually shut down. The second generation of P2P software is Gnutella and Kazaa, which are user-based models. BitTorrent became the third generation of P2P networks. The difference between BitTorrent and previous generations is that it creates a new network for every set of files instead of trying to create one big network of files using SuperNodes, web caches or servers.^[3]

There are a number of factors that contribute to the widespread adoption and facilitation of peer-to-peer file sharing. These include increasing Internet bandwidth, the widespread digitization of physical media files, and the capabilities of home PC's increasing to better handle playing and storing digitized audio and video files. Users were able to transfer either one or more files from one computer to another across the Internet through various file transfers and file-sharing networks.^[4]

Legal aspects[link]

The act of file sharing itself is not illegal and peer-to-peer networks are also used for legitimate purposes, the legal issues in file sharing involve violating the laws of copyrighted material. Most discussions about the legality of "file sharing" are implied to be about solely copyright material. Many countries have some sort of fair use exception that permits limited use of copyrighted material without acquiring permission from the rights holders; such as commentary, news reporting, research and scholarship. Copyrights are territorial- they do not extend beyond the territory of a specific state unless that state is a party to an international agreement. However, most countries today are parties to at least one such agreement.

History[link]

Peer-to-peer file sharing began in 1999 with the introduction of Napster, a file sharing program and central servers that linked people who had files with those who requested files. The central index server was meant to index all of the current users and to search their computers. When someone searched for a file, the server would find all of the available copies of that file and present them to the user. The files would be transferred between the two private computers. One limitation was that only music files could be shared.^[5] Because this process occurred on a central server, however, Napster was held liable for copyright infringement and shut down in July 2001. It later reopened as a pay service.^[6]

After Napster shut down, developers tried to create new ways of sharing files that would not infringe on copyright laws. The most popular of these new services were Gnutella and Kazaa. While Napster connected users through a centralized server, these new services connected users remotely to each other.^[7] These services also allowed users to download files other than music, such as movies and games.^[8]

Another protocol that emerged after Napster shut down is Bittorrent. Bittorrent allows users to connect with more than one peer and download individual pieces from those peers.^[9] Bittorrent users voluntarily upload their files; this contrasts to other services like Napster and Gnutella that search your computer’s hard drive for files and make them available to anyone.^[10]

Economic impact[link]

Main article: Effects of file sharing

There is still ongoing discussion about the economic impact of P2P file-sharing. Norbert Michel, a Policy Analyst at The Heritage Foundation, said that because of "econometric and data issues, studies thus far have produced disparate estimates of file sharing's impact on album sales."^[11]

In the book The Wealth of Networks, Yochai Benkler says that peer-to-peer file sharing is economically efficient and that the users pay the full transaction cost and marginal cost of such sharing even if it "throws a monkey wrench into the particular way in which our society has chosen to pay musicians and re-cording executives. This trades off efficiency for longer-term incentive effects for the recording industry. However, it is efficient within the normal meaning of the term in economics in a way that it would not have been had Jack and Jane used subsidized computers or network connections".^[12]

Economic impact on the music industry[link]

The economic effect of copyright infringement through peer-to-peer filesharing on music revenue has been controversial and difficult to determine. Music sales dropped globally from approximately $38 billion in 1999 to $32 billion in 2003, and an increasing number of studies found that file sharing had a negative impact on record sales.^[13][14][15] It has proven difficult to untangle the cause and effect relationships among a number of different trends, including an increase in legal online purchases of music; illegal file-sharing; drops in the prices of CDs; and the extinction of many independent music stores with a concommitant shift to sales by big-box retailers.^[16]

Economic impact on the film industry[link]

The MPAA reported that American studios lost $2.3 billion to Internet piracy in 2005, representing approximately one third of the total cost of film piracy in the United States.^[17] The MPAA's estimate was doubted by commentators since it was based on the assumption that one download was equivalent to one lost sale, and downloaders might not purchase the movie if illegal downloading was not an option.^[18][19][20] Due to the private nature of the study, the figures could not be publicly checked for methodology or validity,^[21][22][23] and on January 22, 2008, as the MPAA was lobbying for a bill which would compel universities to crack down on piracy, it was admitted that MPAA figures on piracy in colleges had been inflated by up to 300%.^[24][25]

A 2010 study, commissioned by the International Chamber of Commerce and conducted by independent Paris-based economics firm TERA, estimated that unlawful downloading of music, film and software cost Europe's creative industries several billion in revenue each year.^[26] Furthermore, the TERA study entitled “Building a Digital Economy: The Importance of Saving Jobs in the EU's Creative Industries” predicted losses due to piracy reaching as much as 1.2 million jobs and €240 billion in retail revenue by 2015 if the trend continued. Researchers applied a substitution rate of ten percent to the volume of copyright infringements per year. This rate corresponded to the number of units potentially traded if unlawful file sharing were eliminated and did not occur.^[27] Piracy rates of one-quarter or more^[vague] for popular software and operating systems have been common, even in countries and regions with strong intellectual property enforcement, such as the United States or the EU.^[28]

Public perception and usage[link]

In 2004, an estimated 70 million people participated in online file sharing.^[29] According to a CBS News poll, nearly 70 percent of 18 to 29 year olds thought file sharing was acceptable in some circumstances and 58 percent of all Americans who followed the file sharing issue considered it acceptable in at least some circumstances.^[30]

In January 2006, 32 million Americans over the age of 12 had downloaded at least one feature length movie from the Internet, 80 percent of whom had done so exclusively over P2P. Of the population sampled, 40 percent felt that downloading copyrighted movies off the Internet constituted a very serious offense, however 78 percent believed taking a DVD from a store without paying for it constituted a very serious offense.^[31]

In July 2008, 20 percent of Europeans used file sharing networks to obtain music, while 10 percent used paid-for digital music services such as iTunes.^[32]

In February 2009, a Tiscali UK survey found that 75 percent of the English public polled were aware of what was legal and illegal in relation to file sharing, however there was a divide as to where they felt the legal burden should be placed: 49 percent of people believed P2P companies should be held responsible for illegal file sharing on their networks, 18 percent viewed individual file sharers as the culprits, while 18 percent either didn’t know or chose not to answer.^[33]

According to an earlier poll, 75 percent of young voters in Sweden (18-20) supported file sharing when presented with the statement: "I think it is OK to download files from the Net, even if it is illegal." Of the respondents, 38 percent said they "adamantly agreed" while 39 percent said they "partly agreed".^[34]

Risks[link]

Researchers have examined potential security risks including the release of personal information, bundled spyware, and viruses downloaded from the network.^[35][36] Some proprietary file sharing clients have been known to bundle malware, though open source programs typically have not. Some open source file sharing packages have even provided integrated anti-virus scanning.^[37] A drastic increase in inadvertent P2P file sharing of personal and sensitive information became evident in 2009 at the beginning of President Obama's administration when the blueprints to the helicopter Marine One were made available to the public through a breach in security via a P2P file sharing site. Access to this information has the potential of being detrimental to US security.^[38]

Furthermore, shortly before this security breach, the Today show had reported that more than 150,000 tax returns, 25,800 student loan applications and 626,000 credit reports had been inadvertently made available through file sharing.^[38]

Since approximately 2004 identity theft has become more prevalent, and in July 2008 there was another inadvertent revealing of vast amounts of personal information through careless use of a P2P site. The "names, dates of birth, and Social Security numbers of about 2,000 of (an investment) firm's clients" were exposed, "including [those of] Supreme Court Justice Stephen Breyer."^[38]

Researchers have discovered thousands of documents containing sensitive patient information on popular peer-to-peer (P2P) networks, including insurance details, personally identifying information, physician names and diagnosis codes on more than 28,000 individuals. Many of the documents contained sensitive patient communications, treatment data, medical diagnoses and psychiatric evaluations.^[39]

The United States government has attempted to make users more aware of the potential risks involved with P2P file sharing programs through legislation such as H.R. 1319, the Informed P2P User Act.^[40] According to this act, it would be mandatory for individuals to be aware of the risks associated with peer-to-peer file sharing before purchasing software with informed consent of the user required prior to use of such programs. In addition, the act would allow users to block and remove P2P file sharing software from their computers at any time,^[41] with the Federal Trade Commission enforcing regulations.

See also[link]

Internet portal

• Comparison of file sharing applications
• Disk sharing
• File sharing in Canada
• File sharing timeline
• Open Music Model
• Privacy in file sharing networks
• Trade group efforts against file sharing
• Warez
• Torrent poisoning

References[link]

Part of a series on
File sharing
Technologies
Peer to peer BitTorrent File hosting services
Development and societal aspects
Timeline Legal aspects
Non-public file sharing
Anonymous P2P Friend-to-friend Darknet Private P2P
File sharing networks and services
Gnutella / Gnutella2 (G2) FastTrack eDonkey Direct Connect Mininova isoHunt The Pirate Bay ExtraTorrent
By country or region
Canada UK
v t e

File sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia (audio, images and video), documents, or electronic books. It may be implemented through a variety of ways. Common methods of storage, transmission and dispersion include manual sharing utilizing removable media, centralized servers on computer networks, World Wide Web-based hyperlinked documents, and the use of distributed peer-to-peer networking.

Types of file sharing[link]

Peer-to-peer file sharing[link]

Users can use software that connects in to a peer-to-peer network to search for shared files on the computers of other users (i.e. peers) connected to the network. Files of interest can then be downloaded directly from other users on the network. Typically, large files are broken down into smaller chunks, which may be obtained from multiple peers and then reassembled by the downloader. This is done while the peer is simultaneously uploading the chunks it already has to other peers.

History[link]

Files were first exchanged on removable media.^{[citation needed]} Computers were able to access remote files using filesystem mounting, bulletin board systems (1978), Usenet (1979), and FTP servers (1985). Internet Relay Chat (1988) and Hotline (1997) enabled users to communicate remotely through chat and to exchange files. The mp3 encoding, which was standardized in 1991 and which substantially reduced the size of audio files, grew to widespread use in the late 1990s. In 1998, MP3.com and Audiogalaxy were established, the Digital Millennium Copyright Act was unanimously passed, and the first mp3 player devices were launched. MP3.com offered music by unsigned artists, and grew to serve 4 million audio downloads daily.^{[citation needed]}

In June 1999, Napster was released as a centralized unstructured peer-to-peer system,^[1] requiring a central server for indexing and peer discovery. It is generally credited as being the first peer-to-peer file sharing system.

Gnutella, eDonkey2000, and Freenet were released in 2000, as MP3.com and Napster were facing litigation. Gnutella, released in March, was the first decentralized file sharing network. In the gnutella network, all connecting software was considered equal, and therefore the network had no central point of failure. In July, Freenet was released and became the first anonymity network. In September the eDonkey2000 client and server software was released.

In 2001, Kazaa and Poisoned for the Mac was released. Its FastTrack network was distributed, though unlike gnutella, it assigned more traffic to 'supernodes' to increase routing efficiency. The network was proprietary and encrypted, and the Kazaa team made substantial efforts to keep other clients such as Morpheus off of the FastTrack network.

In July 2001, Napster was sued by several recording companies and lost in A&M Records, Inc. v. Napster, Inc..^[2] In the case of Napster, it has been ruled that an online service provider could not use the "transitory network transmission" safe harbor in the DMCA if they had control of the network with a server.^[3]

Shortly after loss in court Napster has been shut down to comply with court order. This drove users to other P2P applications and file sharing continued its growth.^[4] The Audiogalaxy Satellite client grew in popularity, and the LimeWire client and BitTorrent protocol were released. Until its decline in 2004, Kazaa was the most popular file sharing program despite bundled malware and legal battles in the Netherlands, Australia, and the United States. In 2002, a Tokyo district court ruling shut down File Rogue, and the Recording Industry Association of America (RIAA) filed a lawsuit that effectively shut down Audiogalaxy.

Demonstrators protesting The Pirate Bay raid, 2006.

From 2002 through 2003, a number of BitTorrent services were established, including Suprnova.org, isoHunt, TorrentSpy, and The Pirate Bay. In 2002, the RIAA was filing lawsuits against Kazaa users. As a result of such lawsuits, many universities added file sharing regulations in their school administrative codes (though some students managed to circumvent them during after school hours). With the shutdown of eDonkey in 2005, eMule became the dominant client of the eDonkey network. In 2006, police raids took down the Razorback2 eDonkey server and temporarily took down The Pirate Bay.

In 2009, the Pirate Bay trial ended in a guilty verdict for the primary founders of the tracker. The decision was appealed, leading to a second guilty verdict in November 2010. In October 2010, Limewire was forced to shut down following a court order in Arista Records LLC v. Lime Group LLC but the gnutella network remains active through open source clients like Frostwire and gtk-gnutella. Furthermore, multi-protocol file sharing software such as MLDonkey and Shareaza adapted in order to support all the major file sharing protocols, so users no longer had to install and configure multiple file sharing programs.

On 19 January 2012, the United States Department of Justice shut down the popular domain of Megaupload (established 2005). The file sharing site has claimed to have over 50,000,000 people a day.^[5] Kim Dotcom (formerly Kim Schmitz) was arrested in New Zealand and is awaiting extradition.^[6] The case involving the downfall of the world's largest and most popular file sharing site was not well received, with hacker group Anonymous bringing down several sites associated with the take-down.^[5] In the days following this, other file sharing sites began to cease services; Filesonic blocked public downloads on January 22, with Fileserve following suit on January 23.

Legality of file sharing[link]

The legal debate surrounding file sharing has caused many lawsuits. In the United States, some of these lawsuits have even reached the Supreme Court in MGM v. Grokster. In that particular lawsuit, the Supreme Court has ruled that the creators of P2P networks can be held responsible if the intent of their program is clearly to infringe on copyright laws.

On the other hand, file sharing is not necessarily illegal, even if the works being shared are covered by copyright. For example, some artists may choose to support freeware, shareware, open source, or anti-copyright, and advocate the use of file sharing as a free promotional tool. Nearly all freeware, and open source software may be shared, under the rules specified in the license for that specific piece of software. Content in the public domain can also be freely shared.

Ethics of file sharing[link]

In 2004 there were an estimated 70 million people participating in online file sharing.^[7] According to a CBS News poll in 2009, 58% of Americans who follow the file sharing issue, considered it acceptable "if a person owns the music CD and shares it with a limited number of friends and acquaintances"; with 18 to 29 year olds this percentage reached as much as 70%.^[8]

Effects of file sharing[link]

According to David Glenn, writing in The Chronicle of Higher Education, "A majority of economic studies have concluded that file sharing hurts sales".^[9] A literature review by Professor Peter Tschmuck found 22 independent studies on the effects of music file sharing. "Of these 22 studies, 14 – roughly two-thirds – conclude that unauthorized downloads have a 'negative or even highly negative impact' on recorded music sales. Three of the studies found no significant impact while the remaining five found a positive impact."^[10][11][12]

A study by economists Felix Oberholzer-Gee and Koleman Strumpf in 2004 concluded that music file sharing's effect on sales was "statistically indistinguishable from zero".^[13][14] This research was disputed by other economists, most notably Stan Liebowitz, who said Oberholzer-Gee and Strumpf had made multiple assumptions about the music industry "that are just not correct."^[13][15][16] In June 2010, Billboard reported that Oberholzer-Gee and Strumpf had "changed their minds", now finding "no more than 20% of the recent decline in sales is due to sharing".^[17] However, citing Nielsen SoundScan as their source, the co-authors maintained that illegal downloading had not deterred people from being original. "In many creative industries, monetary incentives play a reduced role in motivating authors to remain creative. Data on the supply of new works are consistent with the argument that file sharing did not discourage authors and publishers. Since the advent of file sharing, the production of music, books, and movies has increased sharply."^[18] Glenn Peoples of Billboard disputed the underlying data, saying "SoundScan's number for new releases in any given year represents new commercial titles, not necessarily new creative works."^[19] The RIAA likewise responded that "new releases" and "new creative works" are two separate things. "[T]his figure includes re-releases, new compilations of existing songs, and new digital-only versions of catalog albums. SoundScan has also steadily increased the number of retailers (especially non-traditional retailers) in their sample over the years, better capturing the number of new releases brought to market. What Oberholzer and Strumpf found was better ability to track new album releases, not greater incentive to create them."^[20]

A 2006 study prepared by Birgitte Andersen and Marion Frenz, published by Industry Canada, was "unable to discover any direct relationship between P2P file-sharing and CD purchases in Canada".^[21] The results of this survey were similarly criticized by academics and a subsequent revaluation of the same data by Dr. George R. Barker of the Australian National University reached the opposite conclusion.^[22] "In total, 75% of P2P downloaders responded that if P2P were not available they would have purchased either through paid sites only (9%), CDs only (17%) or through CDs and pay sites (49%). Only 25% of people say they would not have bought the music if it were not available on P2P for free. This clearly suggests P2P network availability is reducing music demand of 75% of music downloaders which is quite contrary to Andersen and Frenz's much published claim."^[23]

Market dominance[link]

A paper in journal Management Science found that file sharing decreased the chance of survival for low ranked albums on music charts and increased exposure to albums that were ranked high on the music charts, allowing popular and well known artists to remain on the music charts more often. This had a negative impact for new and less known artists while promoting the work of already popular artists and celebrities.^[24]

A more recent study that examined pre-release file sharing of music albums, using BitTorrent software, also discovered positive impacts for "established and popular artists but not newer and smaller artists." According to Robert G. Hammond of North Carolina State University, an album that leaked one month early would see a modest increase in sales. "This increase in sales is small relative to other factors that have been found to affect album sales."

"File-sharing proponents commonly argue that file sharing democratizes music consumption by 'leveling the playing field' for new/small artists relative to established/popular artists, by allowing artists to have their work heard by a wider audience, lessening the advantage held by established/popular artists in terms of promotional and other support. My results suggest that the opposite is happening, which is consistent with evidence on file-sharing behavior."^[25]

Billboard cautioned that this research looked only at the pre-release period and not continuous file sharing following a release date. "The problem in believing piracy helps sales is deciding where to draw the line between legal and illegal. ... Implicit in the study is the fact that both buyers and sellers are required in order for pre-release file sharing to have a positive impact on album sales. Without iTunes, Amazon and Best Buy, file-sharers would be just file sharers rather than purchasers. If you carry out the 'file sharing should be legal' argument to its logical conclusion, today's retailers will be tomorrow's file-sharing services that integrate with their respective cloud storage services."^[26]

Availability[link]

Many argue that file-sharing has forced the owners of entertainment content to make it more widely available legally through fee or advertising on demand on the internet, rather than remain static with TV, radio, DVD's, CD's, and the theater. Content for purchase has been higher than illegal in North America aggregate internet traffic since at least 2009. ^[27]As content becomes more available for pay streaming and legal action continues against illegal file sharing, illegal file sharing will likely decline further. ^[28]

See also[link]

Internet portal

• Graduated response
• Comparison of file sharing applications
• Open Music Model
• Privacy in file sharing networks
• Torrent poisoning
• Trade group efforts against file sharing
• Warez
• Missionary Church of Kopimism

References[link]

Further reading[link]

• Levine, Robert. Free Ride: How the Internet Is Destroying the Culture Business and How the Culture Business Can Fight Back, Bodley Head, February 2011.
• Ghosemajumder, Shuman. Advanced Peer-Based Technology Business Models. MIT Sloan School of Management, 2002
• Silverthorne, Sean. Music Downloads: Pirates- or Customers?. Harvard Business School Working Knowledge, 2004.
• Ralf Steinmetz, Klaus Wehrle (Eds). Peer-to-Peer Systems and Applications. ISBN 3-540-29192-X, Lecture Notes in Computer Science, Volume 3485, September 2005
• Stephanos Androutsellis-Theotokis and Diomidis Spinellis. A survey of peer-to-peer content distribution technologies. ACM Computing Surveys, 36(4):335–371, December 2004. doi:10.1145/1041680.1041681.
• Stefan Saroiu, P. Krishna Gummadi, and Steven D. Gribble. A Measurement Study of Peer-to-Peer File Sharing Systems. Technical Report # UW-CSE-01-06-02. Department of Computer Science & Engineering. University of Washington. Seattle, WA, USA.
• Selected Papers — A collection of academic papers.

External links[link]

• Digital Britain

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A peer-to-peer system of nodes without central infrastructure.

Centralized server-based service model (not peer-to-peer).

Peer-to-peer (abbreviated to P2P) refers to a computer network 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 files and peripherals without the need for a central server. P2P networks can be set up in 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 servers supply (send), and clients consume (receive).

The first peer-to-peer application was the file sharing system Napster, originally released in 1999. The concept has inspired new structures and philosophies in many areas of human interaction. Peer-to-peer networking is not restricted to technology; it also covers social processes with a peer-to-peer dynamic. In such context, social peer-to-peer processes are currently emerging throughout society.

Architecture of P2P systems[link]

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 of queries.

In structured peer-to-peer networks, peers (and, sometimes, resources) are organized following specific criteria and algorithms, which lead to overlays with specific topologies and properties. They typically use distributed hash table-based (DHT) indexing, such as in the Chord system (MIT).^[2]

Unstructured peer-to-peer networks do not impose any structure on the overlay networks. Peers in these networks connect in an ad-hoc fashion.^[3] Ideally, unstructured P2P systems would have absolutely no centralized system, but in practice there are several types of unstructured systems with various degrees of centralization. Three categories can easily be seen.

• In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing layer, as there are no preferred nodes with any special infrastructure function.
• Hybrid peer-to-peer systems allow such infrastructure nodes to exist, often called supernodes.^[4]
• In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire system. Although this has similarities with a structured architecture, the connections between peers are not determined by any algorithm.

The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized model.^[5] Freenet and early implementations of the gnutella protocol, on the other hand, are examples of the decentralized model. Modern gnutella implementations, Gnutella2, as well as the now deprecated Kazaa network are examples of the hybrid model.

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 unstructured or structured.

Structured systems[link]

Structured P2P networks employ a globally consistent protocol to ensure that any node can efficiently route a search to some peer that has the desired file, even if the file is extremely rare. Such a guarantee necessitates a more structured pattern of overlay links. By far the most common type of structured P2P network is the distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer, in a way analogous to a traditional hash table's assignment of each key to a particular array slot. Though the term DHT is commonly used to refer to the structured overlay, in practice, DHT is a data structure implemented on top of a structured overlay.^[6]

Distributed hash tables[link]

Distributed hash tables

Distributed hash tables (DHTs) are a class of decentralized distributed systems that provide a lookup service similar to a hash table: (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures.

DHTs form an infrastructure that can be used to build peer-to-peer networks. Notable distributed networks that use DHTs include BitTorrent's distributed tracker, the Kad network, the Storm botnet, YaCy, and the Coral Content Distribution Network.

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).

DHT-based networks have been widely utilized for accomplishing efficient resource discovery^[7][8] for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involves searching for the appropriate resource types that match the user’s application requirements. Recent advances in the domain of decentralized resource discovery have been based on extending the existing DHTs with the capability of multi-dimensional data organization and query routing. Majority of the efforts have looked at embedding spatial database indices such as the Space Filling Curves (SFCs) including the Hilbert curves, Z-curves, k-d tree, MX-CIF Quad tree and R*-tree for managing, routing, and indexing of complex Grid resource query objects over DHT networks. Spatial indices are well suited for handling the complexity of Grid resource queries. Although some spatial indices can have issues as regards to routing load-balance in case of a skewed data set, all the spatial indices are more scalable in terms of the number of hops traversed and messages generated while searching and routing Grid resource queries. 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.^[9]

Unstructured systems[link]

An unstructured P2P network is formed when the overlay links are established arbitrarily. Such networks can be easily constructed as a new peer that wants to join the network can copy existing links of another node and then form its own links over time. In an unstructured P2P network, if a peer wants to find a desired piece of data in the network, the query has to be flooded through the network to find as many peers as possible that share the data. The main disadvantage with such networks is that the queries may not always be resolved. 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. 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. Flooding also causes a high amount of signaling traffic in the network and hence such networks typically have very poor search efficiency. Many of the popular P2P networks are unstructured.

In pure P2P networks: Peers act as equals, merging the roles of clients and server. In such networks, there is no central server managing the network, neither is there a central router. Some examples of pure P2P Application Layer networks designed for peer-to-peer file sharing are gnutella (pre v0.4) and Freenet.

There also exist hybrid P2P systems, which distribute their clients into two groups: client nodes and overlay nodes. Typically, each client is able to act according to the momentary need of the network and can become part of the respective overlay network used to coordinate the P2P structure. This division between normal and 'better' nodes is done in order to address the scaling problems on early pure P2P networks. As examples for such networks can be named modern implementations of gnutella (after v0.4) and Gnutella2.

Another type of hybrid P2P network are networks using on the one hand central server(s) or bootstrapping mechanisms, on the other hand P2P for their data transfers. These networks are in general called 'centralized networks' because of their lack of ability to work without their central server(s). An example for such a network is the eDonkey network (often also called eD2k).

Indexing and resource discovery[link]

Older peer-to-peer networks duplicate resources across each node in the network configured to carry that type of information. This allows local searching, but requires much traffic.

Modern networks use central coordinating servers and directed search requests. Central servers are typically used for listing potential peers (Tor), coordinating their activities (Folding@home), and searching (Napster, eMule). Decentralized searching was first done by flooding search requests out across peers. More efficient directed search strategies, including supernodes and distributed hash tables, are now used.

Peer-to-peer-like systems[link]

In modern definitions of peer-to-peer technology, the term implies the general architectural concepts outlined in this article. However, 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.^[10]

A distributed messaging system that is often likened as an early peer-to-peer architecture is the USENET network news system that is in principle a client–server model from the user or client perspective, when they read or post news articles. 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. Tim Berners-Lee's vision for the World Wide Web, as evidenced by his WorldWideWeb editor/browser, was close to a peer-to-peer design 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. This contrasts to the broadcasting-like structure of the web as it has developed over the years.

Advantages and weaknesses[link]

In P2P networks, clients provide resources, which may include bandwidth, storage space, and computing power. 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. 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. The decentralized nature of P2P networks increases robustness because it removes the single point of failure that can be inherent in a client-server based system.^[11]

Another important property of peer-to-peer systems is the lack of a system administrator. This leads to a network that is easier and faster to setup and keep running because a full staff is not required to ensure efficiency and stability. Decentralized networks introduce new security issues because they are designed so that each user is responsible for controlling their data and resources. Peer-to-peer networks, along with almost all network systems, are vulnerable to unsecure and unsigned codes that may allow remote access to files on a victim's computer or even compromise the entire network. A user may encounter harmful data by downloading a file that was originally uploaded as a virus disguised in an .exe, .mp3, .avi, or any other filetype. This type of security issue is due to the lack of an administrator that maintains the list of files being distributed.

Harmful data can also be distributed on P2P networks by modifying files that are already being distributed on the network. This type of security breach is created by the fact that users are connecting to untrusted sources, as opposed to a maintained server. In the past this has happened to the FastTrack network when the RIAA managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files). Files infected with the RIAA virus were unusable afterwards or even 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.^[12] Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, 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.

There are both advantages and disadvantages in P2P networks related to the topic of data backup, 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 has been pressured by the RIAA, MPAA, 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, only the loss of connection between the clients and server is simple enough to cause a failure, but in P2P networks, the connections between every node must be lost in order to fail to share data. 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, MPAA, and the government are unable to delete or stop the sharing of content on P2P systems.

Social and economic impact[link]

The concept of P2P 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 coined the term commons-based peer production to denote collaborative projects such as free and open source software and Wikipedia. Associated with peer production are the concepts of:

• peer governance (referring to the manner in which peer production projects are managed)
• 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 licenses)
• peer distribution (or the manner in which products, particularly peer-produced products, are distributed)

Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives for resource sharing and cooperation, arguing that the social aspect missing from today's peer-to-peer systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered.^[13] Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory are beginning to take on a more psychological and information-processing direction.

Applications[link]

There are numerous applications of peer-to-peer networks. The most commonly known is for content distribution

Content delivery[link]

• 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^[14]
• 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.
• Peercasting for multicasting streams. See PeerCast, IceShare, FreeCast, Rawflow
• Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare designed for facilitating file sharing among educational institutions globally.
• Osiris (Serverless Portal System) allows its users to create anonymous and autonomous web portals distributed via P2P network.

Exchange of physical goods, services, or space[link]

• 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).

Networking[link]

• 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[link]

• 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[link]

• 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[link]

• 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).

General[link]

• Research like the Chord project, the PAST storage utility, the P-Grid, and the CoopNet content distribution system.
• JXTA, for Peer applications. See Collanos Workplace (Teamwork software), Sixearch

Miscellaneous[link]

• The U.S. Department of Defense has started research on P2P networks as part of its modern network warfare strategy.^[15] In May, 2003 Dr. Tether. Director of Defense Advanced Research Project Agency testified that U.S. Military is using P2P networks.
• Kato et al.’s studies indicate over 200 companies with approximately $400 million USD are investing in P2P network. Besides File Sharing, companies are also interested in Distributing Computing, Content Distribution.
• Wireless community network, Netsukuku
• An earlier generation of peer-to-peer systems were called "metacomputing" or were classed as "middleware". These include: Legion, Globus
• Bitcoin is a peer-to-peer based digital currency.

Historical perspective[link]

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.^[16] This contrasts to the current broadcasting-like structure of the web.

Some networks and channels such as Napster, OpenNAP and IRC serving channels use a client–server structure for some tasks (e.g., searching) and a P2P structure for others. Networks such as gnutella or Freenet use a P2P structure for nearly all tasks, with the exception of finding peers to connect to when first setting up.

P2P architecture embodies one of the key technical concepts of the Internet, described in the first Internet Request for Comments, RFC 1, "Host Software" dated April 7, 1969. More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing servers in architectures used for exchanging multimedia files.

Network neutrality controversy[link]

Peer-to-peer applications present one of the core issues in the network neutrality controversy. Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to its high-bandwidth usage.^[17] Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due to ongoing file transfers and swarm/network coordination packets. In October 2007, Comcast, one of the largest broadband Internet providers in the USA, started blocking P2P applications such as BitTorrent. Their rationale was that P2P is mostly used to share illegal content, and their infrastructure is not designed for continuous, high-bandwidth traffic. Critics point out that P2P networking has legitimate uses, and that this is another way that large providers are trying to control use and content on the Internet, and direct people towards a client-server-based application architecture. The client-server model provides financial barriers-to-entry to small publishers and individuals, and can be less efficient for sharing large files. As a reaction to this bandwidth throttling, several P2P applications started implementing protocol obfuscation, such as the BitTorrent protocol encryption. Techniques for achieving "protocol obfuscation" involves removing otherwise easily identifiable properties of protocols, such as deterministic byte sequences and packet sizes, by making the data look as if it were random.^[18] The ISP's solution to the high bandwidth is P2P caching, where a ISP stores the part of files most accessed by P2P clients in order to save access to the Internet.

See also[link]

• Client–server model
• Decentralized computing
• Friend-to-friend
• List of P2P protocols
• Peercasting
• Segmented downloading
• Semantic P2P networks
• Wireless ad-hoc network
• USB dead drop

References[link]

External links[link]

Wikimedia Commons has media related to: Peer-to-peer software

David Nimmer is an American lawyer, law professor, renowned as an expert in United States copyright law. He received an A.B. with distinction and honors in 1977 from Stanford University and his J.D. in 1980 from Yale Law School, where he served as editor of the Yale Law Journal. David Nimmer is of counsel to Irell & Manella LLP^[1] in Los Angeles, California. He also serves as a Professor from Practice at University of California, Los Angeles Law School and Distinguished Scholar at the Berkeley Center for Law and Technology. In 2000, he was elected to the American Law Institute. He has served as a guest professor at the University of Haifa, Yeshiva University (Cardozo Law School), and the University of Miami.

Nimmer was named the 2010 "Intellectual Property Lawyer of the Year" by the Century City Bar Association.^[2] He was selected a Southern California "Super Lawyer" by Los Angeles Magazine^[3] in 2006-2010 and has been named in The Best Lawyers in America for over 10 years. The Los Angeles and San Francisco Daily Journals named him one of California's "Top 10 Copyright Lawyers" in 2008. In September 2010, he was named one of "The 25 Most Influential People in IP" in The American Lawyer's Fall 2010 Intellectual Property supplement (in the good company of such fellow honorees as Supreme Court justice Anthony Kennedy, PTO Director David Kappos, and Sen. Patrick Leahy.)

Nimmer also served as the Chairman on the Committee on Intellectual Properties Litigation for the American Bar Association from 1989-1992.

Since 1985, Nimmer has updated and revised Nimmer on Copyright, the standard reference treatise in the field, first published in 1963 by his late father, Professor Melville B. Nimmer. Routinely cited by domestic and foreign courts at all levels in copyright litigation, cases within the United States have relied on Nimmer on Copyright as persuasive authority in over 2500 judicial opinions.

He has also contributed to numerous other books, including Le lisibile et l’illsibe (2003), Cases and Materials on Copyright and Other Aspects of Entertainment Litigation (2002), Artefacts and Intellectual Property (2001), Copinger and Skone James on Copyright (1991), OnMultimedia: Technologies for the 21st Century (1990), Droit des affaires (1989), and International Copyright Law and Practice (1989–1998).

He has also composed a series of influential articles. Kluwer Law International collected several dozen into two published anthologies. One is entitled Copyright Illuminated (2008) and the other is Sacred Text, Technology, and the DMCA (2003). At present, along with UCLA colleague Prof. Neil Netanel, he is co-authoring a book for Oxford University Press regarding five centuries of rabbinic copyright responsa, entitled From Maimonides to Microsoft.

He has taught copyright at UCLA Law School for many years, as well as representing clients in the entertainment, publishing, and high-technology fields. He has twice gone to Washington D.C. on behalf of clients whose copyright matters were before the Supreme Court. The first occasion resulted in a unanimous decision in favor of his client, which simultaneously drew the boundaries between copyright and trademark protection. The second matter did likewise, in a decision issued in March 2010 that vitally affects all freelance writers in the country and the databases that present their historical works.

Other litigation highlights include successfully representing Matthew Bender & Co. before the Second Circuit Court of Appeals in its quest to unlock West's effective monopoly on presenting judicial opinions; convincing the Federal Circuit Court of Appeals to rebuff an opponent's attempt to have copyright law control manufacture of a universal garage door opener; and winning a case in the Tenth Circuit Court of Appeals that allowed his client unfettered rights to publish Jesus: A New Revelation. Along the way, other litigated cases have ranged from the status of Winnie-the-Pooh to the collected choreography of Martha Graham to the Google Books settlement in New York City (still pending, for which he represents the interests of Amazon.com).

Nimmer has given congressional testimony on behalf of the United States Telephone Association and the National Association of Broadcasters. In addition, he gave parliamentary testimony in Sydney on behalf of the Combined Newspaper and Magazine Copyright Committee of Australia. He once offered an amicus brief to the Supreme Court of Israel—which took six years to decide the case, in the process declining his offer. He responded by publishing a 223-page article in the Houston Law Review, Copyright in the Dead Sea Scrolls.

He lives in Los Angeles with his wife, Marcia. They have five children.

References[link]

External links[link]

• UCLA Faculty page