Editing Public data network

{{Short description|Data services for the public}}
A '''public data network''' ('''PDN''') is a [[telecommunications network|network]] established and operated by a [[telecommunications]] administration, or a recognized private operating agency, for the specific purpose of providing [[data transmission]] services for the public.

The first public packet switching networks were [[Iberpac|RETD]] in Spain (1972), the experimental [[Packet switching#RCP|RCP]] network in France (1972) and [[Telenet]] in the United States (1975). "Public data network" was the common name given to the collection of [[X.25]] providers, the first of which were Telenet in the U.S. and [[DATAPAC]] in Canada (both in 1976), and [[Transpac (network)|Transpac]] in France (in 1978). The [[International Packet Switched Service]] (IPSS) was the first commercial and international packet-switched network (1978). The networks were interconnected with [[Gateway (telecommunications)|gateways]] using [[X.75]]. These combined networks had large global coverage during the 1980s and into the 1990s. The networks later provided the infrastructure for the early [[Internet]].

== Description ==
[[File:CCITT_SGVII_X25_Advocates.jpg|right|thumb|220x220px|Representatives of PTTs and private companies who championed the development of X.25-based networks and services in Europe, North America and Japan.]]
In communications, a PDN is a [[circuit switched|circuit-]] or [[packet-switched]] network that is available to the public and that can transmit data in digital form. A PDN provider is a company that provides access to a PDN and that provides any of [[X.25]], [[Frame Relay]], or [[cell relay]] ([[Asynchronous Transfer Mode|ATM]]) services.<ref>{{harv|Schatt|1991|p=207}}.</ref> Access to a PDN generally includes a guaranteed bandwidth, known as the [[committed information rate]] (CIR). Costs for the access depend on the guaranteed rate. PDN providers differ in how they charge for temporary increases in required bandwidth (known as surges). Some use the amount of overrun; others use the surge duration.<ref>{{Cite book|url=https://books.google.com/books?id=3EaeBQAAQBAJ|title=Communications Standards: State of the Art Report 14:3|last=Stokes|first=A. V.|date=2014-05-23|publisher=Elsevier|isbn=978-1-4831-6093-1|language=en}}</ref>

=== Public switched data network ===
A '''public switched data network''' ('''PSDN''') is a network for providing data services via a system of multiple [[wide area network]]s, similar in concept to the [[public switched telephone network]] (PSTN).<ref name="bagad">{{cite book |last1=Bagad |url=https://books.google.com/books?id=VfPST6NEggEC&q=psdn&pg=SA6-PA4 |title=Telecommunication Switching Systems and Networks |date=2009 |publisher=Technical Publications |isbn=9788184315905 |pages=344 |access-date=25 November 2016}}</ref> A PSDN may use a variety of switching technologies, including [[packet switching]], [[circuit switching]], and [[message switching]].<ref name="bagad" /> A packet-switched PSDN may also be called a packet-switched data network.<ref>{{cite book |last1=Hura and Singal |url=https://books.google.com/books?id=BViV0PoH_voC&q=psdn&pg=PA529 |title=Data and Computer Communications: Networking and Internetworking |date=2001 |publisher=CRC Press |isbn=9780849309281 |pages=1168 |access-date=25 November 2016}}</ref><ref>{{cite book |last1=Mazda |first1=Fraidoon |url=https://books.google.com/books?id=i5ZNAGQOX18C&q=psdn&pg=PA497 |title=Focal Illustrated Dictionary of Telecommunications |date=2013 |publisher=Taylor & Francis |isbn=9781136121029 |pages=704 |access-date=25 November 2016}}</ref>

Originally the term PSDN referred only to [[Packet Switch Stream]] (PSS), an [[X.25]]-based packet-switched network in the United Kingdom, mostly used to provide leased-line connections between [[local area network]]s and the Internet using  [[permanent virtual circuit]]s (PVCs).<ref>{{Cite journal |last1=Smith |first1=Edward |last2=Miller |first2=Chris |last3=Norton |first3=Jim |date=2023 |title=Evolving and Exploiting Packet Switched Networks |url=https://www.ssrn.com/abstract=4595785 |journal=SSRN Electronic Journal |language=en |doi=10.2139/ssrn.4595785 |issn=1556-5068|url-access=subscription }}</ref> Today, the term may refer not only to Frame Relay and [[Asynchronous Transfer Mode]] (ATM), both providing PVCs, but also to [[Internet Protocol]] (IP), [[GPRS]], and other [[packet-switching]] techniques.

Whilst there are several technologies that are superficially similar to the PSDN, such as [[Integrated Services Digital Network]] (ISDN) and the [[digital subscriber line]] (DSL) technologies, they are not examples of it.<ref>{{Cite book |last=Hardy |first=Daniel |url=https://books.google.com/books?id=dRhHPINWo2AC&pg=PT512 |title=Networks: Internet, Telephony, Multimedia : Convergences and Complementarities |date=2002 |publisher=Springer Nature |isbn=978-2-7445-0144-9 |pages=512 |language=en}}</ref> ISDN utilizes the PSTN circuit-switched network, and DSL uses point-to-point [[circuit switching]] communications overlaid on the PSTN local loop (copper wires), usually utilized for access to a packet-switched broadband IP network.

=== Public data transmission service ===
A '''public data transmission service''' is a [[data transmission]] service that is established and operated by a [[telecommunication]] [[Business administration|administration]], or a recognized private operating agency, and uses a ''public data network''. A public data transmission service may include [[Circuit Switched Data]], [[Packet switching|packet-switched]], and [[leased line]] data transmission.

== History ==
{{Further|Packet switching#X.25 era|X.25#How the CCITT standardized virtual circuits}}
Public packet switching networks came into operation in the 1970s. The first were [[Packet switching#RETD|RETD]] in Spain, in 1972;<ref>{{Cite web |last=Derek Barber |title=The Origins of Packet Switching |url=http://www.cs.man.ac.uk/CCS/res/res05.htm#f |access-date=2024-06-05 |website=Computer Resurrection Issue 5 |quote=The Spanish, dark horses, were the first people to have a public network. They'd got a bank network which they craftily turned into a public network overnight, and beat everybody to the post.}}</ref> the experimental [[Packet switching#RCP|RCP]] in France, also in 1972;<ref>{{cite conference |last=Després |first=R. |author-link=Rémi Després |year=1974 |title=RCP, the Experimental Packet-Switched Data Transmission Service of the French PTT |url=http://rogerdmoore.ca/PS/RCPDEP/RD.html |conference= |pages=171–185 |archive-url=https://web.archive.org/web/20131020142207/http://rogerdmoore.ca/PS/RCPDEP/RD.html |archive-date=2013-10-20 |access-date=2013-08-30 |book-title=Proceedings of ICCC 74 |url-status=dead}}</ref> [[Telenet]] in the United States, which began operation with proprietary protocols in 1975; [[Packet switching#EIN|EIN]] in the [[European Economic Community|EEC]] in 1976; and [[Packet Switch Stream|EPSS]] in the United Kingdom in 1976 (in development since 1969).<ref name=":02">{{Cite web |last1=Smith |first1=Ed |last2=Miller |first2=Chris |last3=Norton |first3=Jim |date=2017 |title=Packet Switching: The first steps on the road to the information society |url=https://www.npl.co.uk/getattachment/about-us/History/Famous-faces/Donald-Davies/UK-role-in-Packet-Switching-(1).pdf.aspx?lang=en-GB |access-date= |website=National Physical Laboratory}}</ref>

Telenet adopted [[X.25]] protocols shortly after they were published in 1976 while [[DATAPAC]] in Canada was the first public data network specifically designed for X.25, also in 1976.<ref name=":0" /> Many other PDNs adopted X.25 when they came into operation, including [[Transpac (network)|Transpac]] in France in 1978, [[Packet switching#Euronet|Euronet]] in the EEC in 1979, [[Packet Switch Stream]] in the United Kingdom in 1980, and [[AUSTPAC]] in Australia in 1982. [[Iberpac]] in Spain adopted X.25 in the 1980s. [[Tymnet]] and [[CompuServe]] in the United States also adopted X.25.

The [[International Packet Switched Service]] (IPSS) was the first commercial and international packet-switched network. It was a collaboration between British and American telecom companies that became operational in 1978.<ref>{{Cite journal|last=Roberts|first=L.G.|date=1978|title=The evolution of packet switching|journal=Proceedings of the IEEE|volume=66|issue=11|pages=1307–1313|doi=10.1109/PROC.1978.11141|s2cid=26876676|issn=1558-2256}}</ref><ref name=":0">{{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 journal|last=Schwartz|first=Mischa|date=2010|title=X.25 Virtual Circuits - TRANSPAC IN France - Pre-Internet Data Networking [History of communications]|journal=IEEE Communications Magazine|volume=48|issue=11|pages=40–46|doi=10.1109/MCOM.2010.5621965|s2cid=23639680|issn=1558-1896}}</ref>

The [[SITA (business services company)|SITA]] Data Transport Network for airlines adopted X.25 in 1981, becoming the world's most extensive packet-switching network.<ref name="history">{{cite web |title=SITA History |url=http://www.sita.aero/about-sita/what-we-do/sita-history |url-status=live |archive-url=https://web.archive.org/web/20120819091302/http://www.sita.aero/about-sita/what-we-do/sita-history |archive-date=19 August 2012 |accessdate=16 August 2012 |work=About SITA > What we do |publisher=SITA}}</ref><ref name=":11">{{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}}</ref><ref>{{Cite web |title=Airline Control System |website=[[IBM]] |url=https://www.ibm.com/downloads/cas/OEYR6Y0X}}</ref>

The networks were interconnected with [[Gateway (telecommunications)|gateways]] using [[X.75]]. These combined networks had large global coverage during the 1980s and into the 1990s.<ref>{{harvnb|Davies|Bressan|2010|pp=[https://books.google.com/books?id=DN-t8MpZ0-wC&pg=PA2 2, 9]}}</ref><ref>{{cite thesis |last1=Ikram |first1=Nadeem |date=1985 |title=Internet Protocols and a Partial Implementation of CCITT X.75 |id={{OCLC|663449435|1091194379}} |url=https://www.proquest.com/openview/678d6e16a1f0ac0470e12db67623ce91/1 |page=2 |quote=Two main approaches to internetworking have come into existence based upon the virtual circuit and the datagram services. The vast majority of the work on interconnecting networks falls into one of these two approaches: The CCITT X.75 Recommendation; The DoD Internet Protocol (IP).}}</ref><ref>{{Cite journal |last1=Unsoy |first1=Mehmet S. |last2=Shanahan |first2=Theresa A. |date=1981 |title=X.75 internetworking of Datapac and Telenet |journal=ACM SIGCOMM Computer Communication Review |volume=11 |issue=4 |pages=232–239 |doi=10.1145/1013879.802679}}</ref>

Over time, other packet-switching technologies, including [[Frame Relay]] (FR) and [[Asynchronous Transfer Mode]] (ATM) gradually replaced X.25.<ref>{{Cite web |last=Titus |first=Tim |title=42 Dead Networking Technologies and What Killed Them |url=https://www.pathsolutions.com/blog/42-dead-networking-technologies |access-date=2023-09-23 |website=www.pathsolutions.com |language=en}}</ref>

Many of these networks later adopted [[Internet protocol suite|TCP/IP]] and provided the infrastructure for the early [[Internet]].<ref>{{Cite book |last1=Council |first1=National Research |url=https://books.google.com/books?id=Jh1pORpfvrQC&pg=PA148 |title=The Unpredictable Certainty: White Papers |last2=Sciences |first2=Division on Engineering and Physical |last3=Board |first3=Computer Science and Telecommunications |last4=Applications |first4=Commission on Physical Sciences, Mathematics, and |last5=Committee |first5=NII 2000 Steering |date=1998-02-05 |publisher=National Academies Press |isbn=978-0-309-17414-5 |language=en}}</ref><ref name="Schatt 1991 200">{{harv|Schatt|1991|p=200}}.</ref>

==See also==
*[[History of the Internet]]
*[[International Network Working Group]]
*[[National research and education network]]
*[[Protocol Wars]]
*[[OSI model]]
*[[X.25#History|X.25 § History]]

==References==
{{Reflist}}
{{FS1037C}}

==Sources==
* {{cite book
|last=Schatt
|first=Stan
|title=Linking LANs: A Micro Manager's Guide
|year=1991
|publisher=McGraw-Hill
|isbn=0-8306-3755-9
}}

[[Category:Telecommunications]]
[[Category:Public sphere|Data network]]
[[Category:X.25]]