Editing Public data network (section)

== 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.