File sharing

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File sharing is a method of distributing electronically stored information such as computer programs and digital media. File sharing can be implemented in a variety of storage and distribution models. Current common models are the centralized server-based approach and the distributed peer-to-peer (P2P) networks.


[edit] Sneakernet

The oldest form of file sharing is Sneakernet (called such because people would physically transfer files from one person to another by walking; using their sneakers). Before network file sharing people would exchange files on Magnetic tape (including audio cassettes, 8-tracks, VHS, Betamax, etc.), floppy disks and other removable media.

[edit] File server-based sharing

The oldest form of network file sharing is the server-based approach in which a network host is designated as a file server. A file server implements at least one network file sharing protocol, such as File Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP), Secure File Transfer Protocol (SFTP), Network File System (protocol) (NFS), Server Message Block (SMB, CIFS), or other network file systems. Computers seeking to access stored files utilize a compatible client-side protocol implementation and either mount an entire remote directory hierarchy within their file system or facilitate access, transfer, and local storage of individual remote files by means of a user application.

[edit] Web-based sharing

Webhosting is also used for file-sharing; it is similar to the server-based approach, but uses the Hypertext Transfer Protocol (HTTP) and related technologies for file transfer. In small communities popular files can be distributed very quickly and efficiently without extra software in addition to the ubiquitous web browsers. Web hosters are independent of each other; therefore contents are not distributed further. Another term for this is one-click hosting.

[edit] File sharing on the social graph

Recently, Facebook opened its API to 3rd party developers which has allowed for a new type of file-sharing service to emerge. and[1] are two examples of companies that have specific Facebook applications that allow file sharing to be easily accomplished between friends.

[edit] Other client-server protocols

  • Audiogalaxy - Service ended in the middle of 2002 .
  • Direct Connect
  • Napster - Closed in its original form in July 2001, since changed to a fee-based service.
  • Scour Exchange - The second exchange network after Napster. No longer exists.
  • Soulseek - Still popular today despite being relatively old, with more than 120,000 users online at any time.

[edit] Peer-to-peer file sharing

Peer-to-peer file sharing is distinct from file trading in that downloading files from a P2P network does not require uploading, although some networks either provide incentives for uploading such as credits or force the sharing of files being currently downloaded.

[edit] First P2P generation: server-client

To understand peer-to-peer file sharing and what was indeed the very first implementation of peer-to-peer file sharing, you need to go back before the popularized form of the Internet as we know it. First use of Peer-to-peer file sharing was on a network similar to the Internet known as WWIVnet. WWIVnet was like FidoNet but it used a distributed model of nodes where traffic was re-routed based on the shortest distance between nodes. It worked very much like the Internet but without a constant always on connection. The Internet existed prior to WWIVnet, but it was only available to academic institutions, governments and large corporations. FidoNet was a hierarchical (server/client) based network thus not peer-to-peer. WWIVnet was the first widely available distributed network model that you could bring to your home. That all being said, it did not have the capability to share files built in. It was not until the introduction of Linker34 by Jayson Cowan did we see the first P2P application over a distributed end user network.[2] Requests for file lists and specific files where handled by the peer much in the same way as second generation peer-to-peer file sharing and no central server was used for this process.

The first generation of peer-to-peer file sharing networks over the Internet had a centralized server system. This system controls traffic amongst the users. The servers store directories of the shared files of the users and are updated when a user logs on. In the centralized peer-to-peer model, a user would send a search to the centralized server of what they were looking for. The server then sends back a list of peers that have the data and facilitates the connection and download. The server-client system is efficient because the central directory is constantly being updated and all users had to be registered to use the program. However, there is only a single point of entry, which could result in a collapse of the network. In addition, it is possible to have out-of-date information or broken links if the server is not refreshed.[3]

The first file-sharing programs on the Internet marked themselves by inquiries to a server, either the data to the download held ready or in appropriate different Peers and so-called Nodes further-obtained, so that one could download there. Two examples were Napster (today using a pay system) and eDonkey2000 in the server version (today, likewise with Overnet and KAD - network decentralized). Another notable instance of peer to peer file sharing, which still has a free version, is Limewire.

[edit] Second P2P generation: decentralization

After Napster encountered legal troubles, Justin Frankel of Nullsoft set out to create a network without a central index server, and Gnutella was the result. Unfortunately, the Gnutella model of all nodes being equal quickly died because of bottlenecks as the network grew from incoming Napster refugees. FastTrack solved this problem by having some nodes be 'more equal than others'.

By electing some higher-capacity nodes to be indexing nodes, with lower capacity nodes branching off from them, FastTrack allowed for a network that could scale to a much larger size. Gnutella quickly adopted this model, and most current peer-to-peer networks implement this design, as it allows for large and efficient networks without central servers, WinMX also falls into this category.

Also included in the second generation are distributed hash tables (DHTs), which help solve the scalability problem by electing various nodes to index certain hashes (which are used to identify files), allowing for fast and efficient searching for any instances of a file on the network. This is not without drawbacks; perhaps most significantly, DHTs do not directly support keyword searching (as opposed to exact-match searching).

The best examples are Gnutella, Kazaa or eMule with Kademlia, whereby Kazaa has still a central server for logging in. eDonkey2000/Overnet, Gnutella, FastTrack and Ares Galaxy have summed up approx. 10.3 million users (as of April 2006, according to This number does not necessarily correspond to the actual number of persons who use these networks; it must be assumed that some use multiple clients for different networks.

BearShare, originally a Gnutella client, should also be included in here somewhere, but I'm not sure where. Bax2x (talk) 02:13, 7 April 2009 (UTC)

[edit] Third P2P generation: indirect and encrypted

The third generation of peer-to-peer networks are those that have anonymity features built in. Examples of anonymous networks are ANts P2P, RShare, Freenet, I2P, GNUnet and Entropy.

A degree of anonymity is realized by routing traffic through other users' clients, which have the function of network nodes. This makes it harder for someone to identify who is downloading or who is offering files. Most of these programs also have strong encryption to resist traffic sniffing.

Friend-to-friend networks only allow already-known users (also known as "friends") to connect to the user's computer, then each node can forward requests and files anonymously between its own "friends'" nodes.

Third-generation networks have not reached mass usage for file sharing because most current implementations incur too much overhead in their anonymity features, making them slow or hard to use. However, in countries where very fast fiber-to-the-home Internet access is commonplace, such as Japan, a number of anonymous file-sharing clients have already reached high popularity.

An example might be: Petra gives a file to Oliver, then Oliver gives the file to Anna. Petra and Anna thus never become acquainted and thus are protected. Often used virtual IP addresses obfuscate the user's network location because Petra only knows the virtual IP of Anna. Although real IPs are always necessary to establish a connection between Petra and Oliver, nobody knows if Anna really requested and Petra really send the file or if they just forward it (As long as they won't tell anyone their virtual IPs). Additionally all transfers are encrypted, so that even the network administrators cannot see what was sent to whom. Example software includes WASTE and Tor. These clients differ greatly in their goals and implementation. WASTE is designed only for small groups and may therefore be considered Darknet; ANts and I2P are public Peer-to-Peer systems, with anonymization provided exclusively by routing reach.

[edit] Fourth P2P generation: streams over P2P

Apart from the traditional file sharing there are services that send streams instead of files over a P2P network. Thus one can hear radio and watch television without any server involved -- the streaming media is distributed over a P2P network. It is important that instead of a treelike network structure, a swarming technology known from BitTorrent is used. Examples include Peercast, Miro and Wuala.


Tree structure

Swarm structure such as BitTorrent

[edit] List of file sharing clients and networks

Ants network

Mute network

  • MUTE network and client

I2P network

  • I2P network
  • I2Phex - Gnutella over I2P
  • iMule - eDonkey (Kademlia) over I2P
  • Vuze - has I2P plugin

Retroshare-Network (F2F Instant Messenger)

other networks or clients

[edit] Copyright issues

Demonstration in Sweden in support of file sharing, 2006.

File sharing has grown in popularity with the proliferation of high-speed Internet connections, and the relatively small file size and high-quality MP3 audio format. File sharing is a legal technology with legal uses, however many users use it to give and accept copyrighted materials without permission or authorization, which makes it copyright infringement.

Despite the existence of various international treaties, there are still sufficient variations between countries to cause significant difficulties in the protection of copyright. Recent years have seen copyright owners challenging file sharing networks, leading to litigation by industry bodies against private individual file sharers. The legal issues surrounding file sharing have been the subject of debate and conferences, especially among lawyers in the entertainment industries.[4]

The challenges facing copyright holders in the face of file sharing systems highlight that current copyright law and enforcement may not be sufficient in dealing with rapidly developing new technologies and uses. Other challenges include ambiguities in the interpretation of copyright law and varying copyright legislations. The high number of individuals engaged in file sharing of copyrighted material means that copyright holders face problems relating to mass litigation and the development of processes for evidence and discovery.

File sharing technology has evolved in response to legal challenges. There are low technical barriers to entry for would-be sharers, and many file sharing approaches now obfuscate or hide the fact that sharing is happening, or the identities of those involved. For example: encryption and darknets. Although it is contested by some whether the transfer of segmented files constitutes copyright infringement in itself based on existing laws, this is not based on any authoritative reading of the law, and no courts have as yet upheld this view.

Further challenges have arisen because of the need to balance self-protection against fair use. A perceived overbalance towards protection (in the form of media that cannot be backed up, cannot be played on multiple systems by the owner, or contains rootkits[5] or irksome security systems inserted by manufacturers), has led to a backlash against protection systems in some quarters. For example, the first crack of AACS was inspired by a perceived unfair restriction on owner usage.[6] However, despite the difficulties in enforcing copyright issues, there has been a recent movement to crack down on file sharing. The fair use (fair dealing in the UK) exceptions from copyright protection are narrowly drawn in most jurisdictions and mostly focus on personal individual use (for example for private study) and do not extend to making available to the world at large. Since young people make up a large portion of those who share files, many Universities have included file sharing regulations in their school administrative codes.

[edit] Economic impact

As files sharing has spread a debate on how the infringement of copyright (in terms of file sharing copyrighted audio and visual content) impacts on legal distribution of especially music. In a broader context commentators have pointed out that the music industry, along with other types of media such as film and TV are having a difficult time adapting to the digital age.[7]

[edit] Music industry

A number of studies have found that file sharing has a negative impact on record sales. Examples of such studies include three papers published in the April 2006 issue of the Journal of Law and Economics (Liebowitz, Rob and Waldfogel, Zentner).[8] Alejandro Zentner notes in another paper published in 2005 [9], that music sales have globally dropped from approximately $38 billion in 1999 to $32 billion in 2003, and that this downward trend coincides with the advent of Napster in June 1999. Using aggregate data Stan J. Liebowitz argues in a series of papers (2005, 2006) that file sharing had a significant negative impact on record sales.

However, a widely cited paper published in February 2007 concludes that file sharing has no negative effect on CD sales. This paper by Olberholzer-Gee and Strumpf,[10] was published in the Journal of Political Economy, and is the only paper which analyzes actual downloads on file sharing networks. Data gathered from tracking downloading on OpenNap servers indicates that most users logged on very rarely and when they did log on they only downloaded a little more than one CD’s worth of songs. To show how these downloads affected album sales they tracked sales and downloads of 500 random albums of varying genres and after doing so found that illegal downloads would only be a small force in the decrease in album sales, possibly even slightly improving album sales of the top albums in stores at the time.[11] CNET staff writer John Borland reports, “even high levels of file-swapping seemed to translate into an effect on album sales that was "statistically indistinguishable from zero".[11]

In March 2007 the Wall Street Journal found that CD sales have dropped 20 percent in one year, which the Wall Street Journal interpreted as the latest sign of the shift in the way people acquire their music. BigChampagne LLC has reported that around one billion songs a month are being traded on illegal file-sharing networks. As a result of this decline in CD sales, a significant amount of record stores are going out of business and “...making it harder for consumers to find and purchase older titles in stores.”[7]

The debate on how file sharing has impacted on the legal sale of music, especially CDs, is underlined by figures showing a decline in music or record stores[citation needed]. According to an article published by the Almighty Institute of Music Retail, an estimation of 900 independent record stores have closed since 2003, leaving 2,700 stores in the USA[citation needed]. Carolyn Draving, the owner of the record store Trac Records, which is closed after 32 years, believes the downfall is a direct result of the illegal internet downloads[citation needed]. She explains that she lost many long-time consumers to the internet and knows for certain that a few stopped coming in because they just downloaded instead. Another owner, Warren Greene of Spinsters Records, claims that nobody buys CDs anymore and that most of his customers have turned to the internet in order to obtain their music.[citation needed]

[edit] Movie industry

On May 31, 2006 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. [12] However, contrary to MPAA statements, several studies and commentators have concluded that one download hardly equals one lost sale, since many downloaders would not purchase the movie if illegal downloading were not an option.[13][14][15] This is especially so as over 20 percent, $1.4 billion, of the $6.1 billion figure represents what is essentially making a non-commercial backups, either virtually on a device or physically on another disc, which is protected under United States law. These numbers are further suspicious due to the private nature of the study, which cannot be publicly checked for methodology or validity.[16][17][18]

On January 22, 2008, it was revealed that the MPAA numbers on piracy in colleges was grossly inflated by up to 300%.[19] This comes at a time when the MPAA are trying to push a bill through which would compel universities to crack down on piracy.[20]

[edit] Software industry

According to Moisés Naím, even in countries and regions with high intellectual property enforcement standards, such as the US or the EU, piracy rates of one-quarter or more for popular software and operating systems are common. The pirated software is distributed through file sharing at unprecedented rates, and according to Naím, software manufacturers dread the "one disc" effect: a phenomenon in which a single counterfeited copy can be propagated until it has taken over an entire country, pushing the legitimate product out of the market.[21]

[edit] Public perception

According to a poll, 75% of young voters in Sweden (18-20) support 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% said they "adamantly agreed" while 39% said they "partly agreed".[22]

In July 2008 the BBC reported that, according to Jupiter Research, a fifth of Europeans use file sharing networks. 10 percent use paid-for digital music services such as iTunes.[23]

In January 2006 the Solutions Research Group found that 32 million Americans over the age of 12 have downloaded at least one feature length movie from the internet, 80 percent of whom have done so excusively over P2P. Of the population sampled only 40 percent felt that downloading copyrighted movies and music off the internet constituted a very serious offense. This is opposed to the 78 percent who would say the same of taking movies and music from a store.[24]

In February 2008 The LA Times Blog published results of a US campus attitude survey which showed that 64 percent of respondents download music regularly through file-sharing networks and other unauthorized sources. The respondents were also asked to rate on a 1 to 7 scale "how nervous they were about being punished for illegal downloading" (1 being "not concerned" and 7 being "extremely concerned"), two-thirds answered 1 (43 percent) or 2 (24 percent). Only 4 percent answered 5 or 6, and none answered 7, "extremely concerned". This is even though RIAA (the Recording Industry Association of America) has sued thousands of students for file sharing since 2003. [25][26]

75% of American citizens polled know what is legal and illegal in relation to their file sharing [27], however, there is a divide as to whom they feel the legal burden should be placed on. The Tiscali UK survey[28] reveals that 49% of people believe P2P companies should be held responsible for illegal file sharing on their networks, while 18% view the individual file sharers as the culprits. Additionally, 18% of Americans either didn’t know or chose not to answer. [29]

Another reason for illegal file sharing is described by Sean Adams, founder and editor of,

"at least half [of peer to peer users] don’t think the music industry does enough to persuade them that such activity is damaging. Some also believe that their illegal activity is mitigated by regularly spending more money on legal content and live gigs." [30]

60% of the general public download music because of a limited budget, according the to Tiscali UK survey. A common attitude concerning music downloading is that of ‘why should one pay for something when they can get it for free?' [31]

[edit] Attacks on peer-to-peer networks

Many peer-to-peer networks are under constant attack by people with a variety of motives.

Examples include:

  • Poisoning attacks (e.g. providing files whose contents are different from the description, aka "spoofing")
  • Polluting attacks (e.g. inserting "bad" chunks/packets into an otherwise valid file on the network)
  • Defection attacks (users or software that make use of the network without contributing resources to it)
  • Insertion of viruses to carried data (e.g. downloaded or carried files may be infected with viruses or other malware)
  • Malware in the peer-to-peer network software itself (e.g. distributed software may contain spyware)
  • Denial of service attacks (attacks that may make the network run very slowly or break completely)
  • Filtering (network operators may attempt to prevent peer-to-peer network data from being carried)
  • Identity attacks (e.g. tracking down the users of the network and harassing or legally attacking them)
  • Spamming (e.g. sending unsolicited information across the network--not necessarily as a denial of service attack)
  • Distributed Denial of Service (a denial of service that attacks multiple host computers)
  • Man-in-Middle (the attacker intercepts files by obtaining the communication between two different users. Attackers can go on to change the information or simply pass it on untouched. This is all done undetected)
  • Sybil attacks (the attacker creates one malicious identity that can be presented as multiple identities allowing the attacker to control a whole portion of the network)
  • Eclipse attack (the attacker first creates a large amount of users, allowing him to obtain control over a portion of the network. The attacker is then able to divide the network into different sub-networks. If the user wants to communicate with another user, it has to go through one of the attacker's many identities)[32]

Most attacks can be defeated or controlled by careful design of the P2P network and through the use of encryption. P2P network defense is in fact closely related to the "Byzantine Generals Problem". However, almost any network will fail when the majority of the peers are trying to damage it, and many protocols may be rendered impotent by far fewer numbers.

[edit] Risks

There are a number of risks associated with using file sharing software. A common risk is inadvertently sharing files that should remain private. With many P2P clients it is not always clear which files are being shared and some may contain personal information such as credit card numbers. In addition running P2P software provides another potential access point to those who may wish to compromise a system. [33]

Some file-sharing software comes bundled with malware such as spyware, viruses, adware, or otherwise privacy-invasive software. Sometimes this unwanted software remains installed on the system even if the original file-sharing software is removed, and can be very difficult to eliminate. In many cases such malware can interfere with the correct operation of web browsers, anti-virus software, anti-spyware and software firewalls; can cause degraded performance on affected systems; and in some cases may secretly compromise a user's privacy or security. Malware is typically bundled with proprietary software, and not those in open source. In most cases it is possible to remove adware and spyware by running spyware removal programs. Such programs can often remove malware without influencing the functionality of the file-sharing software. However, it should be noted that such malware typically only affects users of the Windows operating system.

Some are also concerned about the use of file-sharing systems to distribute adult pornography to children, child pornography to anyone, inflammatory literature, and illegal or "unpopular" material. Novice users may find it difficult to obtain information about which networks, if any, are "safe" for them to use. With experience, users can reduce their exposure to offensive material by structuring their searches carefully (for example, a search limited to audio file types avoids exposure to video and image files).[34]

[edit] See also

[edit] References

  1. ^ FreeDrive | Facebook
  2. ^ [1] Simtel Archive, Originally posted Apr 9, 1994
  3. ^ Understanding Peer-to-Peer Networking and File-Sharing
  4. ^ Will File-Sharing Kill the Copyright Industries? - West LegalEdcenter
  5. ^ See 2005 Sony BMG CD copy protection scandal.
  6. ^ By "Muslix64", written on doom9's forum. See original post and the ensuing AACS encryption key controversy.
  7. ^ a b Wallstreet Journal Website
  8. ^ Stan J. Liebowitz, "File Sharing: Creative Destruction or Just Plain Destruction?"; Rafael Rob and Joel Waldfogel, "Piracy on the High C's: Music Downloading, Sales Displacement, and Social Welfare in a Sample of College Students"; Alejandro Zentner, "Measuring the Effect of File Sharing on Music Purchases", The Journal of Law and Economics, Vol. 49, No. 1 (April 2006)
  9. ^ Alejandro Zentner, "File Sharing and International Sales of Copyrighted Music: An Empirical Analysis with a Panel of Countries", The B.E. Journal of Economic Analysis & Policy, Vol. 5, Issue 1 (2005)
  10. ^ Felix Olberholzer-Gee and Koleman Strumpf, "The Effect of File Sharing on Record Sales: An Empirical Analysis" Journal of Political Economy, 2007, 115(1):1-42; Retrieved on 2008-10-22 from Koleman Strumpf's website
  11. ^ a b Music sharing doesn't kill CD sales, study says - CNET News
  12. ^ "SWEDISH AUTHORITIES SINK PIRATE BAY: Huge Worldwide Supplier of Illegal Movies Told No Safe Harbors for Facilitators of Piracy!" (PDF). MPAA. 2006-05-31. 
  13. ^ Gross, Daniel (2004-11-21). "Does a Free Download Equal a Lost Sale?". The New York Times. Retrieved on 2007-07-16. 
  14. ^ Oberholzer, Felix; Strumpf, Koleman (March 2004). The Effect of File Sharing on Record Sales: An Empirical Analysis. UNC Chapel Hill. 
  15. ^ Schwartz, John (2004-04-05). "A Heretical View of File Sharing". The New York Times. Retrieved on 2007-07-16. 
  16. ^ Fisher, Ken (2006-05-05). "The problem with MPAA's shocking piracy numbers". Ars Technica. Retrieved on 2007-07-15. 
  17. ^ "Movie Piracy Cost 6.1 Billion". 2006-05-03. Retrieved on 2007-07-16. 
  18. ^ "Hollywood study examines costs of film piracy". ZDNet (Reuters). 2006-05-03. Retrieved on 2007-07-16. 
  19. ^ "MPAA admits college piracy numbers grossly inflated". 2008-01-22. Retrieved on 2008-01-22. 
  20. ^ "2008 shaping up to be "Year of Filters" at colleges, ISPs". 2008-01-22. Retrieved on 2008-01-22. 
  21. ^ Moisés Naím, Illicit, How smugglers, traffickers and copycats are hijacking the global economy, Arrow Books, London, 2007, pg.15
  22. ^ The Local - Young voters back file sharing
  23. ^ BBC NEWS | Technology | Warning letters to 'file-sharers'
  24. ^ Solutions Research Group - Movie File-Sharing Booming: Study
  25. ^ Campus attitudes: a microsample | Bit Player | Los Angeles Times
  26. ^ The Georgetown Voice | University warnings and RIAA lawsuits fail to deter file-sharing - September 30, 2004
  27. ^ [2]
  28. ^]
  29. ^
  30. ^
  31. ^
  32. ^ By Baptiste Pretre Attacks on Peer-to-Peer Networking
  33. ^ By M. Eric Johnson, Dan McGuire, Nicholas D. Willey The Evolution of the Peer-to-Peer File Sharing Industry and the Security Risks for Users
  34. ^ Morris, Alan (2003-08-22). "Testimony of Mr. Alan Morris about Pornography, Technology and Process: Problems and Solutions on Peer-to-Peer Networks". United States Senate, Committee on the Judiciary, Washington, DC. Retrieved on 2006-11-20. 

[edit] Further reading

[edit] External links

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