Peer-to-peer

[6] P2P is used in many protocols such as BitTorrent file sharing over the Internet[7] and in personal networks like Miracast displaying and Bluetooth radio.

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".

[9] 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.

[12][13][14] As a precursor to the Internet, ARPANET was a successful peer-to-peer network where "every participating node could request and serve content".

[16] In May 1999, with millions more people on the Internet, Shawn Fanning introduced the music and file-sharing application called Napster.

[23] 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.

[32][33] However, in order to route traffic efficiently through the network, nodes in a structured overlay must maintain lists of neighbors[34] that satisfy specific criteria.

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.

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 that were tested for.

The RIAA is also known to have uploaded fake music and movies to P2P networks in order to deter illegal file sharing.

[48] 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.

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.

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.

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.

Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, over conflicts with copyright law.

Another notable program, Osiris, enables users to create anonymous and autonomous web portals that are distributed via a peer-to-peer network.

Secure Scuttlebutt is a peer-to-peer gossip protocol capable of supporting many different types of applications, primarily social networking.

[59] Artisoft's LANtastic was built as a peer-to-peer operating system where machines can function as both servers and workstations simultaneously.

Cryptocurrencies are peer-to-peer-based digital currencies that use blockchains 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.

[61] Studying the social attributes of P2P networks is challenging due to large populations of turnover, asymmetry of interest and zero-cost identity.

[62][44] 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.

[63] 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.

Some peer-to-peer networks (e.g. Freenet) place a heavy emphasis on privacy and anonymity—that is, ensuring that the contents of communications are hidden from eavesdroppers, and that the identities/locations of the participants are concealed.

[64] Perpetrators of live streaming sexual abuse and other cybercrimes have used peer-to-peer platforms to carry out activities with anonymity.

[66] Fair use exceptions allow limited use of copyrighted material to be downloaded without acquiring permission from the rights holders.

In October 2007, Comcast, one of the largest broadband Internet providers in the United States, started blocking P2P applications such as BitTorrent.

Critics point out that P2P networking has legitimate legal 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.

An important requirement of this process is that results must be reproducible so that other researchers can replicate, validate, and extend existing work.

"[73] Popular simulators that were widely used in the past are NS2, OMNeT++, SimPy, NetLogo, PlanetLab, ProtoPeer, QTM, PeerSim, ONE, P2PStrmSim, PlanetSim, GNUSim, and Bharambe.