public data network

File:CCITT_SGVII_X25_Advocates.jpg

In communications, a PDN is a 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 (ATM) services.{{harv|Schatt|1991|p=207}}. 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.{{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}}

A public switched data network (PSDN) is a network for providing data services via a system of multiple wide area networks, similar in concept to the public switched telephone network (PSTN).{{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}} A PSDN may use a variety of switching technologies, including packet switching, circuit switching, and message switching. A packet-switched PSDN may also be called a packet-switched data network.{{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}}{{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}}

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 networks and the Internet using permanent virtual circuits (PVCs).{{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 }} 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.{{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}} 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.

A public data transmission service is a data transmission service that is established and operated by a telecommunication administration, or a recognized private operating agency, and uses a public data network. A public data transmission service may include Circuit Switched Data, packet-switched, and leased line data transmission.

{{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 RETD in Spain, in 1972;{{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.}} the experimental RCP in France, also in 1972;{{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}} Telenet in the United States, which began operation with proprietary protocols in 1975; EIN in the EEC in 1976; and EPSS in the United Kingdom in 1976 (in development since 1969).{{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}}

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. Many other PDNs adopted X.25 when they came into operation, including Transpac in France in 1978, 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.{{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}}{{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}}{{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}}

The SITA Data Transport Network for airlines adopted X.25 in 1981, becoming the world's most extensive packet-switching network.{{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}}{{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}}{{Cite web |title=Airline Control System |website=IBM |url=https://www.ibm.com/downloads/cas/OEYR6Y0X}}

The networks were interconnected with gateways using X.75. These combined networks had large global coverage during the 1980s and into the 1990s.{{harvnb|Davies|Bressan|2010|pp=[https://books.google.com/books?id=DN-t8MpZ0-wC&pg=PA2 2, 9]}}{{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).}}{{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}}

Over time, other packet-switching technologies, including Frame Relay (FR) and Asynchronous Transfer Mode (ATM) gradually replaced X.25.{{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}}

Many of these networks later adopted TCP/IP and provided the infrastructure for the early Internet.{{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}}{{harv|Schatt|1991|p=200}}.

• History of the Internet
• International Network Working Group
• National research and education network
• Protocol Wars
• OSI model
• X.25 § History

{{Reflist}}

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• {{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

Data network

Category:X.25