Editing X.25 (section)

{{Short description|Standard protocol suite for packet switched wide area network (WAN) communication}}
{{Use dmy dates|date=May 2016}}
{{Infobox technology standard
| title             = X.25
| long_name         = Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit  
| image             = X25-network-diagram-0a.svg
| caption           = 
| status            = In force
| year_started      = 1976
| version           = (10/96)
| version_date      = October 1996
| preview           = 
| preview_date      = 
| organization      = [[ITU-T]]
| committee         = Study Group VII
| base_standards    = 
| related_standards = 
| abbreviation      = 
| domain            = [[Telecommunications network|networking]]
| license           = 
| website           = https://www.itu.int/rec/T-REC-X.25/
}}
'''X.25''' is an [[ITU-T]] standard protocol suite for [[Packet switched network|packet-switched]] [[data communication]] in [[wide area network|wide area networks]] (WAN). It was originally defined by the [[CCITT|International Telegraph and Telephone Consultative Committee]] (CCITT, now ITU-T) in a series of drafts and finalized in a publication known as ''The Orange Book'' in 1976.<ref name="draft1976">CCITT, Study Group VII, ''Draft Recommendation X-25'', March 1976</ref><ref>[http://www.itu.int/ITU-T/studygroups/com17/history.html History of X.25, CCITT Plenary Assemblies and Book Colors]</ref> 

The protocol suite is designed as three conceptual layers, which correspond closely to the lower three layers of the seven-layer [[OSI model|OSI Reference Model]], although it was developed several years before the OSI model (1984).<ref>{{harv|Friend|Fike|Baker|Bellamy|1988|p=242}}</ref><ref>{{harv|Friend|Fike|Baker|Bellamy|1988|p=243}}</ref> It also supports functionality not found in the OSI [[network layer]].<ref>[http://www.itu.int/rec/T-REC-X.28/en/ ITU-T Recommendation X.28].</ref><ref>[http://www.itu.int/rec/T-REC-X.3/en/ ITU-T Recommendation X.3].</ref> An X.25 WAN consists of [[packet switching|packet-switching exchange]] (PSE) nodes as the networking hardware, and [[leased line]]s, [[plain old telephone service]] connections, or [[ISDN]] connections as physical links. 

X.25 was popular with [[telecommunications company|telecommunications companies]] for their [[Public data network|public data networks]] from the late 1970s to 1990s, which provided worldwide coverage. It was also used in [[financial transaction]] systems, such as [[automated teller machine]]s, and by the credit card payment industry.<ref>{{cite web |author=Foregenix<!--they provided, but say Mastercard and/or/with?--> |date=February 2012 |title=X.25 within the Payment Card Industry |url=http://www.mastercard.com/us/company/en/docs/X25_within_the_Payment_Card_Industry.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160304054052/http://www.mastercard.com/us/company/en/docs/X25_within_the_Payment_Card_Industry.pdf |archive-date=4 March 2016 |access-date=25 May 2016 |df=dmy-all}}</ref> However, most users have since moved to the [[Internet protocol suite|Internet Protocol Suite]] (TCP/IP). X.25 is still used, for example by the aviation industry.{{Citation needed|date=May 2024}}