<P> 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 . Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd . 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 . 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 . </P> <P> 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 . </P> <P> 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 . 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 United States, 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 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 . 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 . The ISP's solution to the high bandwidth is P2P caching, where an ISP stores the part of files most accessed by P2P clients in order to save access to the Internet . </P> <P> 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 ." 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 ." </P>

Where would you find a peer to peer network