Editing X.25 (section)

==History==
[[File:CCITT SGVII X25 Advocates.jpg | thumb | 220x124px | right | Representatives of PTTs and private companies who championed the development of X.25-based networks and services in Europe, North America and Japan. Photographed at the CCITT Rapporteur-group meeting of March 1975 in Ottawa, where they drafted the first X.25 proposal.]]
[[File:CCITT SGVIi chairman and X25 Rapporteur and supporters.png | thumb | 220x124px | right | Major contributors to CCITT X.25, photographed just after its approval in March 1976.]]
The [[CCITT]] (later [[ITU-T]]), the organization responsible for international standardization of telecom services, began developing a standard for packet-switched data communication in the mid-1970s based upon a number of emerging data network projects.<ref name="Sirbu1985">{{cite web |last1=Sirbu |first1=Marvin A |last2=Zwimpfer |first2=Laurence E |date=March 1985 |title=Standards Setting for Computer Communication: The Case of X.25 |url=https://www.academia.edu/2850947 |publisher=IEEE}}</ref> Participants in the design of X.25 included engineers from Canada, France, Japan, the UK, and the USA representing a mix of national [[Postal, telegraph and telephone service|PTTs]] (France, Japan, UK) and private operators (Canada, USA). In particular, the work of [[Rémi Després]], contributed significantly to the standard, which was based on a [[virtual circuit]] service. A few minor changes, which complemented the proposed specification, were accommodated to enable [[Lawrence Roberts (scientist)|Larry Roberts]] to join the agreement.<ref>{{Cite journal|last=Despres|first=Remi|date=2010|title=X.25 Virtual Circuits - TRANSPAC in France - Pre-Internet Data Networking|journal=IEEE Communications Magazine|volume=48|issue=11|pages=40–46|doi=10.1109/MCOM.2010.5621965|issn=1558-1896}}</ref><ref>{{Cite journal|last=Rybczynski|first=Tony|date=2009|title=Commercialization of packet switching (1975-1985): A Canadian perspective [History of Communications]|journal=IEEE Communications Magazine|volume=47|issue=12|pages=26–31|doi=10.1109/MCOM.2009.5350364|s2cid=23243636|issn=1558-1896}}</ref><ref>{{Cite web|url=https://www.itu.int/en/ITU-T/studygroups/com17/Pages/history.aspx|title=Short History of Study Group ... 7|website=www.itu.int|access-date=2020-02-04}}</ref> Various updates and additions were worked into the standard, eventually recorded in the ITU series of technical books describing the telecommunication systems. These books were published every fourth year with different-colored covers. The X.25 specification is part of the larger set of X-Series.<ref>[http://www.itu.int/rec/T-REC-X/en/ X-Series recommendations]</ref><ref name="Friend 1988 230">{{harv|Friend|Fike|Baker|Bellamy|1988|p=230}}</ref>

=== How the CCITT standardized virtual circuits ===
{{anchor|How the CCITT standardized virtual circuits}}
{{See also|Protocol Wars}}
The CCITT appointed a special Rapporteur on packet switching, [[Halvor Bothner-By]], who held an initial meeting in January 1974. This resulted in a question, to be answered by study group (SG) VII for the next CCITT plenary in 1976, which was “Should the packet-node of operation be provided on public data networks and, if so, how should it be implemented?”. A list of packet switching networks “to be considered” was provided: [[ARPANET]] (of the [[Advanced Research Projects Agency|ARPA]] in the USA), [[Packet switching#EIN|EIN]] (of the European COST), [[Packet Switch Stream#EPSS|EPSS]] (of the British [[Post Office Telecommunications]]),[[Packet switching#RCP| RCP]] (of the [[Postes, Télégraphes et Téléphones|French PTT]]), [[CYCLADES]] (of [[French Institute for Research in Computer Science and Automation|IRIA]] in France), the [[NPL network]] (of the [[National Physical Laboratory (United Kingdom)|NPL]] in the UK), the SWIFT network (of the international [[SWIFT|SWIFT society]]), and the [[Packet switching#SITA Data Transport Network|SITA network]] (of the international [[SITA (business services company)|SITA company]]).<ref>{{cite web |last=Bothner-By |first=Halvor |date=July 1974 |title=REPORT OF THE RAPPORTEUR'S GROUP ON POINT C - |url=https://umedia.lib.umn.edu/item/p16022coll270:13778}}</ref>

The second Rapporteur meeting, hosted in Oslo by the Norwegian Telecommunications Administration in November 1974, gathered 24 participants, including representatives of other international organizations ([[International Organization for Standardization|ISO]], [[International Federation for Information Processing|IFIP]], [[Ecma International|ECMA]]).<ref name="ccitt1974-08">{{cite web |last=Rapporteur group on packet switching |title=Report of Meeting in Oslo (15 - 16 AUGUST 1974) |url=https://umedia.lib.umn.edu/item/p16022coll270:13778/p16022coll270:13739?child_index=116&query=&sidebar_page=39 |publisher=CCITT}}</ref> A document submitted by France “with the active support of a number of European administrations” served as “main basis for discussion in this meeting”. It was then “agreed that two types of services should be considered, a ‘datagram’ service and a ‘virtual call’ service”.{{r|ccitt1974-08|p=p3}}

At the third meeting, focus had moved from whether there should be packet-mode networks to whether there could be “a standard for the interface between the network and the computers”.{{r|Sirbu1985|p=p39}}

Starting in January 1975, several bilateral and multilateral meetings took place between network operators having commitments for a packet switching service, in view to draft a common interface specification. Meetings started between the Canadian [[DATAPAC]] and the French [[Transpac (data network)|TRANSPAC]], continued with the startup [[Telenet]] of the USA, and continued with the BPO of the UK.{{r|Sirbu1985|p=p39}}{{r|:20|p=p44}}

In March 1975, Halvor Bothner-By produced a list of recommendations to be created, or simply updated, for a packet switching standard to become possible. It was used as a framework at a drafting meeting in Ottawa between engineers of the four operators wishing to have a standard as soon as possible in the USA, Canada, France, UK and Japan. They prepared contributions to be submitted to SG VII in their name by administrations having voting right in CCITT. One contribution was a X.2x interface specification, the first version of  what will become X.25).<ref>{{cite web |last=CCITT Rapporteur on packet switching |date=March 26, 1975 |title=Proposals for Recommendations |url=https://www.dropbox.com/scl/fi/zc7pc47nfku3wytj3mqcs/1975-03-26-CCITT-Bothner-BY-Proposals-for-Recommendations.pdf?rlkey=g3e8o8a4y8wulel9lf3mh7qh2&dl=0 }}</ref><ref name=":4">{{cite journal |last1=Rybczynski |first1=Tony |date=December 2009 |title=Commercialization of packet switching (1975-1985): A Canadian perspective [History of Communications] |journal=IEEE Communications Magazine |volume=47 |issue=12 |pages=26–31 |doi=10.1109/MCOM.2009.5350364 |s2cid=23243636}}</ref>

The fourth Rapporteur meeting, in May 1975 in Geneva, had 45 participants and 27 new documents. The Rapporteur asked whether packet switching recommendations should be issued "with a view to making international interworking possible”, "the French administration answered in the affirmative and Canada strongly supported the French proposal". No firm conclusion was however obtained yet.<ref name="CcittMay1975">{{cite web |last=INWG#99 |title=Report of the Meeting in Geneva (28 May - 6 June 1975) (Extracts) |url=https://umedia.lib.umn.edu/item/p16022coll270:13610/p16022coll270:13465?child_index=90&query=&sidebar_page=31}}</ref>

The fifth Rapporteur meeting, in September 1975 in Geneva, had about 60 participants. After discussions on the proposed virtual circuit interface, numerous issues were left unresolved.{{r|Sirbu1985|p=p40}} Concerning datagrams, ‘It was proposed by Larry Roberts of the US delegation and supported by representatives from France and Canada respectively that the datagram classification be changed from “E” to “A”’, i.e., from essential "to be available internationally” to additional that "may be available in certain countries and internationally”.<ref>{{cite web |last=Pouzin |first=Louis |date=October 1975 |title=Meeting of the CCITT Rapporteur group on packet switching – (Geneva, 16 – 19 September 1975) |url=https://umedia.lib.umn.edu/item/p16022coll270:13610/p16022coll270:13486?child_index=111&query=&sidebar_page=38 |page=6 in Annex 4}}</ref> The Rapporteur's last report expressed doubts “that a standard would be ready for adoption by SG VII”.{{r|Sirbu1985|p=p40}}

At the last meeting of the full SG VII before the CCITT plenary of September 1976, the available draft X.25 raised numerous clarification questions and/or and technical objections. SG VII's chairman Vern MacDonald appointed an editor and provided a meeting facility for the weekend. After intense work during it, all issues had been dealt with. For an approval by the full study group, a challenge remained: copies of the updated X.25 draft had to be available in two languages. To get them in due time, Tony Rybczynski of DATAPAC and Paul Guinaudeau of TRANSPAC spent a full night to handwrite all negotiated amendments, and to assemble them with paste and scissors into clean documents. COM VII then reviewed distributed copies, and unanimously approved them for submission to the forthcoming CCITT plenary. <ref name=":20">{{Cite journal |last=Després |first=Rémi |date=2010 |editor-last=Schwartz |editor-first=Mischa |title=X.25 Virtual Circuits – TRANSPAC In France – Pre-Internet Data Networking |journal=IEEE Communications Magazine |volume=48 |issue=11 |pages=40–46 |doi=10.1109/MCOM.2010.5621965 |s2cid=23639680}}</ref> At this plenary of September 1976, the X.25 recommendation and the other 10 of SG VII were unanimously approved.{{r|Sirbu1985|p=p40}}

As requested by the USA, an optional datagram service was added to the revised X.25 of 1980, together with an alignment of its link layer, now called LAPB, with a recent evolution of HDLC in [[ISO]]. In absence of any public network operator implementing this option, datagrams were finally deleted from X.25 in its update of 1984.{{r|Sirbu1985|p=p41}}

=== Worldwide public data networks ===
{{Main|Public data network}}
Publicly accessible X.25 networks, commonly called [[Public data network|public data networks]], were set up in many countries during the late 1970s and 1980s to lower the cost of accessing various [[online service]]s. Examples include [[Iberpac]], [[Transpac (network)|TRANSPAC]], [[Compuserve]], [[Tymnet]], [[Telenet]], [[Packet switching#Euronet|Euronet]], [[Packet Switch Stream|PSS]], [[Datapac]], [[Packet-switched network#Datanet 1|Datanet 1]] and [[AUSTPAC]] as well as the [[International Packet Switched Service]]. Their combined network had large global coverage during the 1980s and into the 1990s.<ref name="Schatt 1991 200">{{harv|Schatt|1991|p=200}}.</ref>

Beginning in the early 1990s, in North America, use of X.25 networks (predominated by Telenet and Tymnet)<ref name="Schatt 1991 200" /> started to be replaced by [[Frame Relay]] services offered by national telephone companies.<ref>{{harv|Schatt|1991|p=207}}.</ref> Most systems that required X.25 now use [[TCP/IP]], however it is possible to transport X.25 over TCP/IP when necessary.<ref>{{cite web |date=1 February 2001 |title=Running X.25 over TCP/IP on Cisco routers |url=http://www.techrepublic.com/article/running-x25-over-tcpip-on-cisco-routers/1056023 |archive-url=https://web.archive.org/web/20120121002501/http://www.techrepublic.com/article/running-x25-over-tcpip-on-cisco-routers/1056023 |archive-date=21 January 2012}}</ref>

X.25 networks are still in use throughout the world. A variant called [[AX.25]] is used widely by [[amateur radio|amateur]] [[packet radio]]. [[Racal]] Paknet, now known as Widanet, remains in operation in many regions of the world, running on an X.25 protocol base. In some countries, like the Netherlands or Germany, it is possible to use a stripped version of X.25 via the [[Integrated Services Digital Network#Bearer channel|D-channel]] of an [[ISDN]]-2 (or [[basic rate interface|ISDN BRI]]) connection for low-volume applications such as [[point-of-sale]] terminals; but, the future of this service in the Netherlands is uncertain.

X.25 is still used in the aeronautical business (especially in Asia) even though a transition to modern protocols is increasingly important as X.25 hardware becomes increasingly rare and costly.{{Clarify|date=April 2013}} As recently as March 2006,<!-- still used?--> the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with [[air route traffic control center]]s.

France was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as [[Minitel]] it was based on [[Videotex]], itself running on X.25. In 2002, [[Minitel]] had about 9 million users, and in 2011 it accounted for about 2 million users in France when France Télécom announced it would shut down the service by 30 June 2012.<ref>{{in lang|fr}} {{cite news |last=Presse |first=Agence France |date=21 July 2011 |title=Le Minitel disparaîtra en juin 2012 |language=fr |trans-title=Minitel will disappear in June 2012 |newspaper=Le Figaro |url=http://www.lefigaro.fr/flash-actu/2011/07/21/97001-20110721FILWWW00446-le-minitel-disparaitra-en-juin-2012.php}}</ref> As planned, service was terminated 30 June 2012. There were 800,000 terminals in operation at the time.<ref>{{in lang|fr}}[http://www.zdnet.fr/actualites/minitel-dernier-rappel-arret-definitif-le-30-juin-2012-39769465.htm]</ref> An X.25 service was still purchasable from BT in the United Kingdom in 2019.<ref>{{Cite web |title=BT price list: Section 13:BT IP Networking |url=https://www.bt.com/pricing/current/BT_IP_Networking_boo/2-0177_d0e27.htm |access-date=30 May 2019 |website=BT}}</ref>