Peer-to-peer
This article's tone or style may not reflect the encyclopedic tone used on Wikipedia. (April 2021) |
Peer-to-peer (P2P) computing or networking is a
Peers make a portion of their resources, such as processing power, disk storage, or
While P2P systems had previously been used in many
Development
While P2P systems had previously been used in many application domains,[4] the concept was popularized by file sharing systems such as the music-sharing application Napster. 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".[6] 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.[7]
Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links. The early Internet was more open than the present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures.[8][6][page needed] This contrasts with the broadcasting-like structure of the web as it has developed over the years.[9][10][11] As a precursor to the Internet, ARPANET was a successful peer-to-peer network where "every participating node could request and serve content". However, ARPANET was not self-organized, and it could not "provide any means for context or content-based routing beyond 'simple' address-based routing."[11]
Therefore,
In May 1999, with millions more people on the Internet, Shawn Fanning introduced the music and file-sharing application called Napster.[11] 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".[11]
Architecture
A peer-to-peer network is designed around the notion of equal
Routing and resource discovery
Peer-to-peer networks generally implement some form of virtual
Unstructured networks
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.[16] (Gnutella, Gossip, and Kazaa are examples of unstructured P2P protocols).[17]
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.[18] 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.[19][20]
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
Structured networks
In structured peer-to-peer networks the overlay is organized into a specific topology, and the protocol ensures that any node can efficiently[22] search the network for a file/resource, even if the resource is extremely rare.[17]
The most common type of structured P2P networks implement a distributed hash table (DHT),[23][24] in which a variant of consistent hashing is used to assign ownership of each file to a particular peer.[25][26] This enables peers to search for resources on the network using a hash table: that is, (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key.[27][28]
However, in order to route traffic efficiently through the network, nodes in a structured overlay must maintain lists of neighbors[29] 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).[20][30] 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.[31]
Notable distributed networks that use DHTs include
Hybrid models
Hybrid models are a combination of peer-to-peer and client–server models.[35] A common hybrid model is to have a central server that helps peers find each other. Spotify was an example of a hybrid model [until 2014].[citation needed] 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.[36]
CoopNet content distribution system
CoopNet (Cooperative Networking) was a proposed system for off-loading serving to peers who have recently
Security and trust
Peer-to-peer systems pose unique challenges from a computer security perspective.
Like any other form of software, P2P applications can contain vulnerabilities. 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.[39]
Routing attacks
Since each node plays a role in routing traffic through the network, malicious users can perform a variety of "routing attacks", or
Corrupted data and malware
The prevalence of
Corrupted data can also be distributed on P2P networks by modifying files that are already being shared on the network. For example, on the
Resilient and scalable computer networks
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.[44] 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
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.[45]
In a P2P network, the community of users is entirely responsible for deciding which content is available. Unpopular files eventually disappear and become unavailable as fewer people share them. Popular files, however, are highly and easily distributed. Popular files on a P2P network are more stable and available than files on central networks. In a centralized network, a simple loss of connection between the server and clients can cause a failure, but in P2P networks, the connections between every node must be lost 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 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.[46]
Applications
This article is in prose. is available. (September 2014) |
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
File-sharing networks
Many peer-to-peer file sharing networks, such as Gnutella, 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[50]
- Software publication and distribution (Linux distribution, several games); via file sharing 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 law.[51] Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd..[52] 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 and PDTP protocols.
- Some proprietary multimedia applications use a peer-to-peer network along with streaming servers to stream audio and video to their clients.
- Peercasting for multicasting streams.
- Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare designed for facilitating file sharing among educational institutions globally.
- Osirisis a program that allows its users to create anonymous and autonomous web portals distributed via P2P network.
Other P2P applications
- Dat, a distributed version-controlled publishing platform.
- anonymously.
- Unlike the related I2P, the onion services.
- The distributed file system.
- Jami, a peer-to-peer chat and SIP app.
- Java platform.
- Netsukuku, a Wireless community network designed to be independent from the Internet.
- Open Garden, connection sharing application that shares Internet access with other devices using Wi-Fi or Bluetooth.
- Resilio Sync, a directory-syncing app.
- Research like the CoopNet content distribution system.
- Secure Scuttlebutt, a peer-to-peer gossip protocol, capable of supporting many different types of applications, primarily social networking.
- Syncthing, a directory-syncing app.
- M-commerceapplications that power real-time marketplaces.
- The U.S. Department of Defense is conducting research on P2P networks as part of its modern network warfare strategy.[53] In May, 2003, Anthony Tether, then director of DARPA, testified that the United States military uses P2P networks.
- WebTorrent Desktop stand alone version that bridges WebTorrent and BitTorrentserverless networks.
- Microsoft in Windows 10 uses a proprietary peer-to-peer technology called "Delivery Optimization" to deploy operating system updates using end-users PCs either on the local network or other PCs. According to Microsoft's Channel 9 it led to a 30%-50% reduction in Internet bandwidth usage.[54]
- Artisoft's LANtastic was built as a peer-to-peer operating system. Machines can be both servers and workstations at the same time.
- Hotline Communications Hotline Client was built as decentralized servers with tracker software dedicated to any type of files and still operates today.
- Cryptocurrencies are peer-to-peer-based digital currencies which use blockchains.
Social implications
Incentivizing resource sharing and cooperation
Cooperation among a community of participants is key to the continued success of P2P systems aimed at casual human users; these reach their full potential only when large numbers of nodes contribute resources. But in current practice, P2P networks often contain large numbers of users who utilize resources shared by other nodes, but who do not share anything themselves (often referred to as the "freeloader problem"). Freeloading can have a profound impact on the network and in some cases can cause the community to collapse.[55] In these types of networks "users have natural disincentives to cooperate because cooperation consumes their own resources and may degrade their own performance".[56] Studying the social attributes of P2P networks is challenging due to large populations of turnover, asymmetry of interest and zero-cost identity.[56] A variety of incentive mechanisms have been implemented to encourage or even force nodes to contribute resources.[57][58]
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 P2P systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered.[59] 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.
Privacy and anonymity
Some peer-to-peer networks (e.g.
Perpetrators of
Political implications
Intellectual property law and illegal sharing
Although peer-to-peer networks can be used for legitimate purposes, rights holders have targeted peer-to-peer over the involvement with sharing copyrighted material. 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, primarily over issues surrounding copyright law.[51] Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd.[52] In both of the cases the file sharing technology was ruled to be legal as long as the developers had no ability to prevent the sharing of the copyrighted material. To establish criminal liability for the copyright infringement on peer-to-peer systems, the government must prove that the defendant infringed a copyright willingly for the purpose of personal financial gain or commercial advantage.[62] Fair use exceptions allow limited use of copyrighted material to be downloaded without acquiring permission from the rights holders. These documents are usually news reporting or under the lines of research and scholarly work. Controversies have developed over the concern of illegitimate use of peer-to-peer networks regarding public safety and national security. When a file is downloaded through a peer-to-peer network, it is impossible to know who created the file or what users are connected to the network at a given time. Trustworthiness of sources is a potential security threat that can be seen with peer-to-peer systems.[63]
A study ordered by the European Union found that illegal downloading may lead to an increase in overall video game sales because newer games charge for extra features or levels. The paper concluded that piracy had a negative financial impact on movies, music, and literature. The study relied on self-reported data about game purchases and use of illegal download sites. Pains were taken to remove effects of false and misremembered responses.[64][65][66]
Network neutrality
Peer-to-peer applications present one of the core issues in the
Current research
Researchers have used computer simulations to aid in understanding and evaluating the complex behaviors of individuals within the network. "Networking research often relies on simulation in order to test and evaluate new ideas. An important requirement of this process is that results must be reproducible so that other researchers can replicate, validate, and extend existing work."[69] If the research cannot be reproduced, then the opportunity for further research is hindered. "Even though new simulators continue to be released, the research community tends towards only a handful of open-source simulators. The demand for features in simulators, as shown by our criteria and survey, is high. Therefore, the community should work together to get these features in open-source software. This would reduce the need for custom simulators, and hence increase repeatability and reputability of experiments."[69]
Popular simulators that were widely used in the past are NS2, OMNeT++, SimPy, NetLogo, PlanetLab, ProtoPeer, QTM, PeerSim, ONE, P2PStrmSim, PlanetSim, GNUSim, and Bharambe.[70]
Besides all the above stated facts, there has also been work done on ns-2 open source network simulators. One research issue related to free rider detection and punishment has been explored using ns-2 simulator here.[71]
See also
- Client-to-client protocol
- Client–queue–client
- Cultural-historical activity theory (CHAT)
- Distributed Data Management Architecture
- End-to-end principle
- Friend-to-friend
- List of P2P protocols
- Peer-to-peer energy trading
- Semantic P2P networks
- Sharing economy
- SponsorChange
- USB dead drop
- Wireless ad hoc network
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External links
- Ghosh Debjani, Rajan Payas, Pandey Mayank P2P-VoD Streaming: Design Issues & User Experience Challenges Archived 2017-02-19 at the Wayback Machine Springer Proceedings, June 2014
- Glossary of P2P terminology
- Foundation of Peer-to-Peer Computing, Special Issue, Elsevier Journal of Computer Communication, (Ed) Javed I. Khan and Adam Wierzbicki, Volume 31, Issue 2, February 2008
- Anderson, Ross J. "The eternity service". Pragocrypt. 1996.
- Marling Engle & J. I. Khan. Vulnerabilities of P2P systems and a critical look at their solutions Archived 2007-06-15 at the Wayback Machine, May 2006
- Stephanos Androutsellis-Theotokis and Diomidis Spinellis. A survey of peer-to-peer content distribution technologies Archived 2020-11-09 at the Wayback Machine. ACM Computing Surveys, 36(4):335–371, December 2004.
- Biddle, Peter, Paul England, Marcus Peinado, and Bryan Willman, The Darknet and the Future of Content Distribution Archived 2011-07-27 at the Wayback Machine. In 2002 ACM Workshop on Digital Rights Management, November 2002.
- John F. Buford, Heather Yu, Eng Keong Lua P2P Networking and Applications. ISBN 0123742145, Morgan Kaufmann, December 2008
- Djamal-Eddine Meddour, Mubashar Mushtaq, and Toufik Ahmed, "Open Issues in P2P Multimedia Streaming Archived 2011-08-22 at the Wayback Machine", in the proceedings of the 1st Multimedia Communications Workshop MULTICOMM 2006 held in conjunction with IEEE ICC 2006 pp 43–48, June 2006, Istanbul, Turkey.
- Detlef Schoder and Kai Fischbach, "Core Concepts in Peer-to-Peer (P2P) Networking Archived 2011-09-15 at the Wayback Machine". In: Subramanian, R.; Goodman, B. (eds.): P2P Computing: The Evolution of a Disruptive Technology, Idea Group Inc, Hershey. 2005
- Ramesh Subramanian and Brian Goodman (eds), Peer-to-Peer Computing: Evolution of a Disruptive Technology, ISBN 1-59140-429-0, Idea Group Inc., Hershey, PA, United States, 2005.
- Shuman Ghosemajumder. Advanced Peer-Based Technology Business Models Archived 2012-10-13 at the Wayback Machine. MIT Sloan School of Management, 2002.
- Silverthorne, Sean. Music Downloads: Pirates- or Customers? Archived 2006-06-30 at the Wayback Machine. Harvard Business School Working Knowledge, 2004.
- Glasnost Archived 2014-10-05 at the Wayback Machine test P2P traffic shaping (Max Planck Institute for Software Systems)