Editing BitTorrent (section)

== Associated technologies ==
=== Distributed trackers ===
On 2 May 2005, Azureus 2.3.0.0 (now known as [[Vuze]]) was released,<ref>{{cite web|url=http://azureus.sourceforge.net/changelog.php|title=Vuze Changelog|publisher=Azureus.sourceforge.net|url-status=live|archive-url=https://web.archive.org/web/20061201095553/http://azureus.sourceforge.net/changelog.php|archive-date=1 December 2006}}</ref> utilizing a distributed database system. This system is a [[distributed hash table]] implementation which allows the client to use torrents that do not have a working [[BitTorrent tracker]]. A bootstrap server is instead utilized. The following month, BitTorrent, Inc. released version 4.2.0 of the Mainline BitTorrent client, which supported an alternative DHT implementation (popularly known as "[[Mainline DHT]]", outlined in a draft on their website) that is incompatible with that of Azureus. In 2014, measurement showed concurrent users of Mainline DHT to be from 10 million to 25&nbsp;million, with a daily churn of at least 10&nbsp;million.<ref>{{cite journal|last1=Wang|first1=Liang|last2=Kangasharju|first2=Jussi.|year=2013|title=Measuring Large-Scale Distributed Systems: Case of BitTorrent Mainline DHT|url=https://www.cs.helsinki.fi/u/lxwang/publications/P2P2013_13.pdf|url-status=live|journal=IEEE Peer-to-Peer|archive-url=https://web.archive.org/web/20140512225743/http://www.cs.helsinki.fi/u/lxwang/publications/P2P2013_13.pdf|archive-date=12 May 2014|access-date=15 May 2014|df=dmy-all}}</ref>

Current versions of the official BitTorrent client, [[μTorrent]], [[BitComet]], [[Transmission (BitTorrent client)|Transmission]] and BitSpirit all share compatibility with Mainline DHT. Both DHT implementations are based on [[Kademlia]].<ref>{{cite web|url=http://khashmir.sourceforge.net/ |title=Khashmir.SourceForge.net |publisher=Khashmir.SourceForge.net |access-date=9 July 2012 | archive-url = https://web.archive.org/web/20120702140624/http://khashmir.sourceforge.net/ | archive-date = 2 July 2012| url-status=live}}</ref> As of version 3.0.5.0, Azureus also supports Mainline DHT in addition to its own distributed database through use of an optional application plugin.<ref>{{cite web|url=http://azureus.sourceforge.net/plugin_details.php?plugin=mlDHT|title=plugins.vuze.com|publisher=plugins.vuze.com|url-status=live|archive-url=https://web.archive.org/web/20120801195122/http://azureus.sourceforge.net/plugin_details.php?plugin=mlDHT|archive-date=1 August 2012|access-date=9 July 2012}}</ref> This potentially allows the Azureus/Vuze client to reach a bigger swarm.

Another idea that has surfaced in Vuze is that of ''virtual torrents''. This idea is based on the distributed tracker approach and is used to describe some web resource. Currently, it is used for [[instant messaging]]. It is implemented using a special messaging protocol and requires an appropriate plugin. Anatomic P2P is another approach, which uses a decentralized network of nodes that route traffic to dynamic trackers. Most BitTorrent clients also use [[peer exchange]] (PEX) to gather peers in addition to [[BitTorrent tracker|trackers]] and [[Distributed hash table|DHT]]. Peer exchange checks with known peers to see if they know of any other peers. With the 3.0.5.0 release of Vuze, all major BitTorrent clients now have compatible peer exchange.

=== Web seeding ===
{{Further|Torrent file#HTTP seeds}}

Web "seeding" was implemented in 2006 as the ability of BitTorrent clients to download torrent pieces from an HTTP source in addition to the "swarm". The advantage of this feature is that a website may distribute a torrent for a particular file or batch of files and make those files available for download from that same web server; this can simplify long-term seeding and [[Load balancing (computing)|load balancing]] through the use of existing, cheap, web hosting setups. In theory, this would make using BitTorrent almost as easy for a web publisher as creating a direct HTTP download. In addition, it would allow the "web seed" to be disabled if the swarm becomes too popular while still allowing the file to be readily available. This feature has two distinct specifications, both of which are supported by [[Libtorrent]] and the 26+ clients that use it.

The first was created by John "TheSHAD0W" Hoffman, who created BitTornado.<ref>{{cite web |url=http://bittornado.com/docs/webseed-spec.txt |title=HTTP-Based Seeding Specification |format=TXT |publisher=BitTornado.com |access-date=9 May 2006 |archive-url=https://web.archive.org/web/20040320142756/http://www.bittornado.com/docs/webseed-spec.txt |archive-date=20 March 2004 |url-status=dead|df=dmy }}</ref><ref>{{cite web|url=https://www.bittorrent.org/beps/bep_0017.html|title=''HTTP Seeding'' – BitTorrent Enhancement Proposal № 17|author=John Hoffman, DeHackEd|date=25 February 2008|url-status=live|archive-url=https://web.archive.org/web/20131213074432/http://www.bittorrent.org/beps/bep_0017.html|archive-date=13 December 2013|access-date=17 February 2012}}</ref> This first specification requires running a web service that serves content by info-hash and piece number, rather than filename.

The other specification is created by [[GetRight]] authors and can rely on a basic HTTP download space (using [[byte serving]]).<ref>{{cite web |url=http://www.getright.com/seedtorrent.html|title=HTTP/FTP Seeding for BitTorrent |publisher=GetRight.com|access-date=18 March 2010 |archive-url = https://web.archive.org/web/20091228072458/http://getright.com/seedtorrent.html |archive-date = 28 December 2009| url-status=live}}</ref><ref>{{cite web|url=https://www.bittorrent.org/beps/bep_0019.html|title=''WebSeed – HTTP/FTP Seeding (GetRight style)'' – BitTorrent Enhancement Proposal № 19|author=Michael Burford|date=25 February 2008|publisher=Bittorrent.org|url-status=live|archive-url=https://web.archive.org/web/20131213074337/http://www.bittorrent.org/beps/bep_0019.html|archive-date=13 December 2013|access-date=17 February 2012}}</ref>

In September 2010, a new service named Burnbit was launched which generates a torrent from any URL using webseeding.<ref name="tf-article">{{cite web|url=https://torrentfreak.com/burn-any-web-hosted-file-into-a-torrent-with-burnbit-100913/|title=Burn Any Web-Hosted File into a Torrent With Burnbit|date=13 September 2010|publisher=TorrentFreak|url-status=live|archive-url=https://web.archive.org/web/20110809053857/http://torrentfreak.com/burn-any-web-hosted-file-into-a-torrent-with-burnbit-100913/|archive-date=9 August 2011|access-date=9 July 2012}}</ref> There are server-side solutions that provide initial seeding of the file from the web server via standard BitTorrent protocol and when the number of external seeders reach a limit, they stop serving the file from the original source.<ref name="web-seeders">{{cite web|url=http://php-tracker.org/ |title=PHP based torrent file creator, tracker and seed server |publisher=PHPTracker |access-date=9 July 2012 | archive-url = https://web.archive.org/web/20131219084439/http://php-tracker.org/ | archive-date = 19 December 2013| url-status=live}}</ref>

=== RSS feeds ===
{{Main|Broadcatching}}

A technique called [[broadcatching]] combines [[RSS (file format)|RSS]] feeds with the BitTorrent protocol to create a content delivery system, further simplifying and automating content distribution. Steve Gillmor explained the concept in a column for [[Ziff-Davis]] in December 2003.<ref>Gillmor, Steve (13 December 2003). {{cite web |url=http://www.eweek.com/c/a/Messaging-and-Collaboration/BitTorrent-and-RSS-Create-Disruptive-Revolution/ |title=BitTorrent and RSS Create Disruptive Revolution |date=14 December 2003 |publisher=EWeek.com |access-date=22 April 2007 }}</ref> The discussion spread quickly among bloggers (Ernest Miller,<ref>Miller, Ernest (2 March 2004). {{cite web |url=http://importance.corante.com/archives/002223.html |title=BitTorrent + RSS = The New Broadcast | archive-url = https://web.archive.org/web/20131023060205/http://importance.corante.com/archives/002223.html | archive-date = 23 October 2013| url-status=live}}. ''The Importance of...'' Corante.com.</ref> [[Chris Pirillo]], etc.). In an article entitled ''Broadcatching with BitTorrent'', Scott Raymond explained:

{{blockquote|I want RSS feeds of BitTorrent files. A script would periodically check the feed for new items, and use them to start the download. Then, I could find a trusted publisher of an [[Alias (TV Show)|Alias]] RSS feed, and "subscribe" to all new episodes of the show, which would then start downloading automatically&nbsp;– like the "season pass" feature of the [[TiVo]].|Scott Raymond| scottraymond.net<ref>{{cite web|author=Raymond, Scott |url=http://scottraymond.net/archive/4745 |archive-url=https://web.archive.org/web/20040213093750/http://scottraymond.net/archive/4745 |archive-date=13 February 2004|title=Broadcatching with BitTorrent|publisher=scottraymond.net|date= 16 December 2003}}</ref>}}

The RSS feed will track the content, while BitTorrent ensures content integrity with [[cryptography|cryptographic]] [[Hash function|hashing]] of all data, so feed subscribers will receive uncorrupted content. One of the first and popular software clients ([[free software|free]] and [[open source software|open source]]) for ''broadcatching'' is [[Miro Media Player|Miro]]. Other free software clients such as PenguinTV and KatchTV are also now supporting broadcatching. The BitTorrent web-service MoveDigital added the ability to make torrents available to any web application capable of parsing [[XML]] through its standard [[Representational State Transfer|REST]]-based interface in 2006,<ref>{{cite web| url=http://www.movedigital.com/docs/index.php/MoveDigital_API| title=MoveDigital API REST functions| publisher=Move Digital|year=2006 |archive-url=https://web.archive.org/web/20060811154118/http://www.movedigital.com/docs/index.php/MoveDigital_API |archive-date=11 August 2006 |access-date=9 May 2006}} Documentation.</ref> though this has since been discontinued. Additionally, Torrenthut is developing a similar torrent [[API]] that will provide the same features, and help bring the torrent community to [[Web 2.0]] standards. Alongside this release is a first [[PHP]] application built using the API called PEP, which will parse any [[Really Simple Syndication]] (RSS 2.0) feed and automatically create and seed a torrent for each enclosure found in that feed.<ref>{{cite web|url=http://prodigem.com/code/pep/pep.txt | title=Prodigem Enclosure Puller(pep.txt)| publisher=Prodigem.com| format=TXT| access-date=9 May 2006 |archive-url = https://web.archive.org/web/20060526130219/http://prodigem.com/code/pep/pep.txt |archive-date = 26 May 2006}} via [[Internet Wayback Machine]].</ref><!-- – wi-fizzle unreachable 2007-4-15&nbsp;– found in Google cache&nbsp;– identical to archive.org copy. --Lexein -->

=== Throttling and encryption ===
{{Main|BitTorrent protocol encryption}}

Since BitTorrent makes up a large proportion of total traffic, some [[ISP]]s have chosen to "throttle" (slow down) BitTorrent transfers. For this reason, methods have been developed to disguise BitTorrent traffic in an attempt to thwart these efforts.<ref>{{cite web|url=https://torrentfreak.com/encrypting-bittorrent-to-take-out-traffic-shapers/|title=Encrypting Bittorrent to take out traffic shapers|date=5 February 2006|publisher=Torrentfreak.com|url-status=live|archive-url=https://web.archive.org/web/20140326092903/http://torrentfreak.com/encrypting-bittorrent-to-take-out-traffic-shapers/|archive-date=26 March 2014|access-date=9 May 2006}}</ref> Protocol header encrypt (PHE) and [[BitTorrent protocol encryption|Message stream encryption/Protocol encryption (MSE/PE)]] are features of some BitTorrent clients that attempt to make BitTorrent hard to detect and throttle. As of November 2015, [[Vuze]], [[BitComet]], [[KTorrent]], [[Transmission (BitTorrent client)|Transmission]], [[Deluge (BitTorrent client)|Deluge]], [[μTorrent]], MooPolice, Halite, [[qBittorrent]], [[rTorrent]], and the latest official BitTorrent client (v6) support MSE/PE encryption.

In August 2007, [[Comcast]] was preventing BitTorrent seeding by monitoring and interfering with the communication between peers. Protection against these efforts is provided by [[proxy server|proxying]] the client-tracker traffic via an [[tunneling protocol|encrypted tunnel]] to a point outside of the Comcast network.<ref>{{cite web|url=https://torrentfreak.com/comcast-throttles-bittorrent-traffic-seeding-impossible/|title=Comcast Throttles BitTorrent Traffic, Seeding Impossible|url-status=live|archive-url=https://web.archive.org/web/20131011044156/http://torrentfreak.com/comcast-throttles-bittorrent-traffic-seeding-impossible/|archive-date=11 October 2013}}, ''TorrentFreak'', 17 August 2007.</ref> In 2008, Comcast called a "truce" with BitTorrent, Inc. with the intention of shaping traffic in a protocol-agnostic manner.<ref>{{cite web|url=https://www.cnet.com/news/comcast-and-bittorrent-agree-to-collaborate/|title=Comcast and BitTorrent Agree to Collaborate|last=Broache|first=Anne|date=27 March 2008|publisher=News.com|url-status=live|archive-url=https://web.archive.org/web/20080509150131/http://www.news.com/8301-10784_3-9904494-7.html|archive-date=9 May 2008|access-date=9 July 2012}}</ref> Questions about the ethics and legality of Comcast's behavior have led to renewed debate about [[net neutrality in the United States]].<ref>{{cite web|url=https://www.cnet.com/news/is-comcasts-bittorrent-filtering-violating-the-law/|title=Is Comcast's BitTorrent filtering violating the law?|last=Soghoian|first=Chris|date=4 September 2007|website=Cnet.com|url-status=live|archive-url=https://web.archive.org/web/20100715153001/http://www.cnet.com/8301-13739_1-9769645-46.html|archive-date=15 July 2010|access-date=9 July 2012}}</ref> In general, although encryption can make it difficult to determine ''what'' is being shared, BitTorrent is vulnerable to [[traffic analysis]]. Thus, even with MSE/PE, it may be possible for an ISP to recognize BitTorrent and also to determine that a system is no longer downloading but only uploading data, and terminate its connection by injecting [[Transmission Control Protocol|TCP]] RST (reset flag) packets.

=== Multitrackers ===
Another unofficial feature is an extension to the BitTorrent metadata format proposed by John Hoffman<ref>{{cite web|url=https://www.bittorrent.org/beps/bep_0012.html|title=BEP12: Multitracker Metadata Extension|publisher=BitTorrent Inc.|url-status=live|archive-url=https://web.archive.org/web/20121227233108/http://bittorrent.org/beps/bep_0012.html|archive-date=27 December 2012|access-date=28 March 2013}}</ref> and implemented by several indexing websites. It allows the use of multiple trackers per file, so if one tracker fails, others can continue to support file transfer. It is implemented in several clients, such as [[BitComet]], BitTornado, BitTorrent, [[KTorrent]], [[Transmission (BitTorrent client)|Transmission]], [[Deluge (software)|Deluge]], [[μTorrent]], [[rtorrent]], [[Vuze]], and [[Frostwire]]. Trackers are placed in groups, or tiers, with a tracker randomly chosen from the top tier and tried, moving to the next tier if all the trackers in the top tier fail.

Torrents with multiple trackers can decrease the time it takes to download a file, but also have a few consequences:
* Poorly implemented<ref>{{cite web| url=http://wiki.depthstrike.com/index.php/P2P:Protocol:Specifications:Multitracker#Bad_Implementations| title=P2P:Protocol:Specifications:Multitracker| access-date=13 November 2009| publisher=wiki.depthstrike.com| archive-url=https://web.archive.org/web/20140326095037/http://wiki.depthstrike.com/index.php/P2P%3AProtocol%3ASpecifications%3AMultitracker#Bad_Implementations| archive-date=26 March 2014| url-status=live| df=dmy-all}}{{dubious|reason=Wikis are not citable sources – find a better source-Lexein|date=April 2013}}</ref> clients may contact multiple trackers, leading to more overhead-traffic.
* Torrents from closed trackers suddenly become downloadable by non-members, as they can connect to a seed via an open tracker.

=== Peer selection ===
{{As of|2008|12|post=,}} BitTorrent, Inc. was working with Oversi on new Policy Discover Protocols that query the ISP for capabilities and network architecture information. Oversi's ISP hosted NetEnhancer box is designed to "improve peer selection" by helping peers find local nodes, improving download speeds while reducing the loads into and out of the ISP's network.<ref>{{cite web|last=Johnston |first=Casey |url=https://arstechnica.com/news.ars/post/20081209-bittorrent-has-new-plan-to-shape-up-p2p-behavior.html |title=Arstechnica.com |publisher=Arstechnica.com |date=9 December 2008 |access-date=9 July 2012 | archive-url = https://web.archive.org/web/20081212061637/http://arstechnica.com/news.ars/post/20081209-bittorrent-has-new-plan-to-shape-up-p2p-behavior.html | archive-date = 12 December 2008| url-status=live}}</ref>