Editing Explicit Congestion Notification (section)

{{short description|Extension to the Internet Protocol to signal network congestion}}
{{IPstack}}

'''Explicit Congestion Notification''' ('''ECN''') is an extension to the [[Internet Protocol]] and to the [[Transmission Control Protocol]] and is defined in {{IETF RFC|3168}} (2001). ECN allows end-to-end notification of [[network congestion]] without dropping packets. ECN is an optional feature that may be used between two ECN-enabled endpoints when the underlying network infrastructure also supports it.

Conventionally, TCP/IP networks signal congestion by dropping packets.  When ECN is successfully negotiated, an ECN-aware router may set a mark in the IP header instead of dropping a packet in order to signal impending congestion.  The receiver of the packet echoes the congestion indication to the sender, which reduces its transmission rate as if it detected a dropped packet.

Rather than responding properly or ignoring the bits, some outdated or faulty network equipment has historically dropped or mangled packets that have ECN bits set.<ref>{{cite web |url=http://conferences.sigcomm.org/imc/2011/docs/p171.pdf |title=Measuring the State of ECN Readiness in Servers, Clients, and Routers |author1=Steven Bauer |author2=Robert Beverly |author3=Arthur Berger |publisher=Internet Measurement Conference 2011 |date=2011 |url-status=live |archive-url=https://web.archive.org/web/20140322043254/http://conferences.sigcomm.org/imc/2011/docs/p171.pdf |archive-date=2014-03-22 }}</ref><ref>{{cite web|url=http://conferences.sigcomm.org/imc/2004/papers/p336-medina.pdf|title=Measuring Interactions Between Transport Protocols and Middleboxes|author1=Alberto Medina|author2=Mark Allman|author3=Sally Floyd|publisher=Internet Measurement Conference 2004|url-status=live|archive-url=https://web.archive.org/web/20160304084141/http://conferences.sigcomm.org/imc/2004/papers/p336-medina.pdf |archive-date=2016-03-04}}</ref><ref>{{cite web |url=http://www.icir.org/tbit/ecn-tbit.html |title=TBIT, the TCP Behavior Inference Tool: ECN |publisher=Icir.org |access-date=2014-03-22 |url-status=live |archive-url=https://web.archive.org/web/20130311202346/http://www.icir.org/tbit/ecn-tbit.html |archive-date=2013-03-11 }}</ref> {{As of|2015}}, measurements suggested that the fraction of [[web server]]s on the public Internet for which setting ECN prevents network connections had been reduced to less than 1%.<ref>{{cite web |url=http://ecn.ethz.ch/ecn-pam15.pdf |title=Enabling Internet-Wide Deployment of Explicit Congestion Notification |author1=Brian Trammell |author2=Mirja Kühlewind |author3=Damiano Boppart |author4=Iain Learmonth |author5=Gorry Fairhurst |author6=Richard Scheffenegger |publisher=Proceedings of the Passive and Active Measurement Conference 2015 |date=2015 |access-date=14 June 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150615083912/http://ecn.ethz.ch/ecn-pam15.pdf |archive-date=15 June 2015 }}</ref>

Passive support has existed in Ubuntu Linux since 12.04 and in Windows Server since 2012.<ref name="2017stats">{{cite web |url=http://profiles.murdoch.edu.au/myprofile/david-murray/files/2012/06/An_Analysis_of_Changing_Enterprise_Network_Traffic_Characteristics-22.pdf |title=An Analysis of Changing Enterprise Network Traffic Characteristics |author1=David Murray |author2=Terry Koziniec |author3=Sebastian Zander |author4=Michael Dixon |author5=Polychronis Koutsakis |publisher=The 23rd Asia-Pacific Conference on Communications (APCC 2017) |date=2017 |access-date=3 October 2017 |url-status=live |archive-url=https://web.archive.org/web/20171003124654/http://profiles.murdoch.edu.au/myprofile/david-murray/files/2012/06/An_Analysis_of_Changing_Enterprise_Network_Traffic_Characteristics-22.pdf |archive-date=3 October 2017 }}</ref> Passive support in the most popular websites has increased from 8.5% in 2012 to over 70% in May 2017.<ref name="2017stats" /> Adoption across the Internet now requires clients to actively request ECN. In June 2015, [[Apple Inc.|Apple]] announced that ECN will be enabled by default on its supported and future products, to help drive the adoption of ECN signaling industry-wide.<ref name="apple-wwdc-719">{{cite web|url=https://developer.apple.com/videos/wwdc/2015/?id=719|title=Your App and Next Generation Networks|publisher=Apple Inc.|date=2015|url-status=live|archive-url=https://web.archive.org/web/20150615162041/https://developer.apple.com/videos/wwdc/2015/?id=719|archive-date=2015-06-15}}</ref>