Micro Transport Protocol

Micro Transport Protocol or μTP (sometimes also uTP) is an open UDP-based variant of the BitTorrent peer-to-peer file sharing protocol intended to mitigate poor latency and other congestion control problems found in conventional BitTorrent over TCP, while providing reliable, ordered delivery.

It was devised to automatically slow down[1] the rate at which packets of data are transmitted between users of peer-to-peer file sharing torrents when it interferes with other applications. For example, the protocol should automatically allow the sharing of an ADSL line between a BitTorrent application and a web browser.


μTP emerged from research at Internet2 on QoS and high-performance bulk transport, was adapted for use as a background transport protocol by Plicto, that was founded by Stanislav Shalunov[2] and later it was acquired by BitTorrent, Inc. in 2006, and further developed within its new owner.[3] It was first introduced in the μTorrent 1.8.x beta branches, and publicized in the alpha builds of μTorrent 1.9.[4][5]

The implementation of μTP used in μTorrent was later separated into the "libutp" library and published under the MIT license.[6][7]

The first free software client to implement μTP was KTorrent 4.0.[8][9] libtorrent implements μTP since version 0.16.0[10] and it is used in qBittorrent since 2.8.0.[11] Tixati implements μTP since version 1.72.[12] Vuze (formerly Azureus) implements μTP since version[13] Transmission implements μTP since version 2.30.[14]

μTP congestion control

The congestion control algorithm used by μTP, known as Low Extra Delay Background Transport (LEDBAT), aims to decrease the latency caused by applications using the protocol while maximizing bandwidth when latency is not excessive.[15][16] Additionally, information from the μTP congestion controller can be used to choose the transfer rate of TCP connections.[17]

LEDBAT is described in RFC 6817. As of 2009, the details of the μTP implementation were different from those of the then-current Internet Draft.[18]

μTP also adds support for NAT traversal using UDP hole punching between two port-restricted peers where a third unrestricted peer acts as a STUN server.[19][20]

See also


  1. "Archived copy". Archived from the original on March 1, 2010. Retrieved November 15, 2009.CS1 maint: archived copy as title (link)
  2. This Is How Your BitTorrent Downloads Move So Fast, Fastcolabs, 2013-07-29, Retrieved November 6, 2013
  3. http://www.slideshare.net/eCommConf/eric-klinker-presentation-at-emerging-communication-conference-awards-2010-america/11 uTP timeline, slide 11, "This Green Revolution-improving the yield of your network investment", eComm America Conference, San Francisco, CA, April 2010.
  4. µTorrent's switch to UDP and why the sky isn't falling
  5. uTorrent shifts towards UDP to make it work better
  6. "Archived copy". Archived from the original on 2011-01-23. Retrieved 2011-01-15.CS1 maint: archived copy as title (link)
  7. https://github.com/bittorrent/libutp
  8. http://torrentfreak.com/ktorrent-first-bittorrent-client-to-adopt-open-source-utp-100528/
  9. http://ktorrent.pwsp.net/?q=node/42 Archived 2015-04-02 at the Wayback Machine
  10. https://code.google.com/p/libtorrent/downloads/detail?name=libtorrent-rasterbar-0.16.0.tar.gz
  11. http://www.qbittorrent.org/news.php
  12. http://www.tixati.com/news/
  13. https://wiki.vuze.com/w/Version_4400_4702_Changelog
  14. https://trac.transmissionbt.com/wiki/Changes#version-2.30
  15. Technical information about UDP
  16. "Archived copy". Archived from the original on March 1, 2010. Retrieved November 15, 2009.CS1 maint: archived copy as title (link)
  17. "Post by developer "Greg Hazel" in thread "μTorrent 1.9 alpha"". 2008-11-26. Archived from the original on February 8, 2009. Retrieved 2009-03-08.
  18. "Archived copy". Archived from the original on July 25, 2011. Retrieved November 15, 2009.CS1 maint: archived copy as title (link)
  19. "Archived copy". Archived from the original on March 25, 2013. Retrieved December 23, 2012.CS1 maint: archived copy as title (link)
  20. "Archived copy". Archived from the original on June 19, 2013. Retrieved December 23, 2012.CS1 maint: archived copy as title (link)
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