View source for Packet switching

{{short description|Method for transmitting data over a computer network}}
{{Use American English|date=November 2022}}

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| link1             = Paul Baran
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| footer            = [[Paul Baran]] and [[Donald Davies]] independently invented the concept of digital packet switching used in modern computer networking including the Internet.<ref name=":16"/><ref name="Pelkeyp42" /><ref name="NIHF2007"/>
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In [[telecommunications]], '''packet switching''' is a method of grouping [[Data (computing)|data]] into short messages in fixed format, i.e., ''[[network packet|packets]],'' that are transmitted over a [[telecommunications network]]. Packets consist of a [[header (computing)|header]] and a [[payload (computing)|payload]]. Data in the header is used by networking hardware to direct the packet to its destination, where the payload is extracted and used by an [[operating system]], [[application software]], or [[Protocol stack|higher layer protocols]]. Packet switching is the primary basis for [[data communication]]s in [[computer networks]] worldwide.

During the early 1960s, American engineer [[Paul Baran]] developed a concept he called ''distributed adaptive message block switching'' as part of a research program at the [[RAND Corporation]], funded by the [[United States Department of Defense]]. His proposal was to provide a [[fault-tolerant]], efficient method for communication of voice messages using low-cost hardware to route the message blocks across a distributed network. His ideas contradicted then-established principles of [[Bandwidth allocation|pre-allocation of network bandwidth]], exemplified by the development of telecommunications in the [[Bell System]]. The new concept found little resonance among network implementers until the independent work of Welsh computer scientist [[Donald Davies]] at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] beginning in 1965. Davies developed the concept for data communication using software switches in a high-speed computer network and coined the term ''packet switching''. His work inspired numerous packet switching networks in the decade following, including the incorporation of the concept into the design of the [[ARPANET]] in the United States and the [[CYCLADES]] network in France. The ARPANET and CYCLADES were the primary precursor networks of the modern [[Internet]].

==Concept==
[[File:Packet Switching.gif|thumb|350px|This animation illustrates a network model in which consecutive packets between hosts take differing routes. Out-of-order delivery is, however, detrimental to the performance of several network protocols, including TCP, so [[Internet|the Internet]] attempts to route packets associated with the same [[data stream]] along the same path most of the time.<ref>{{cite IETF| rfc=2991| title=Multipath Issues in Unicast and Multicast Next-Hop Selection| date=November 2000}}</ref>]]

A simple definition of packet switching is:
{{blockquote|The [[routing]] and transferring of data by means of addressed packets so that a [[Communication channel|channel]] is occupied during the [[transmission (telecommunications)|transmission]] of the packet only, and upon completion of the transmission the channel is made available for the transfer of other [[network traffic|traffic]].<ref>{{cite book|first=Martin|last=Weik|url=https://books.google.com/books?id=ZCYBCAAAQBAJ&q=packet-switching&pg=PA718|title=Fiber Optics Standard Dictionary|publisher=Springer Science & Business Media|date=6 December 2012|isbn=978-1461560234}}</ref><ref>{{cite book|author=National Telecommunication Information Administration|url=https://books.google.com/books?id=xSa_AAAAQBAJ&q=addressed+packets+of+data&pg=SL16-PA1|title=Telecommunications: Glossary of Telecommunications Terms|publisher=[[Government Institutes]]|date=1 April 1997|isbn=1461732328|volume=1037, Part 3 of Federal Standard}}</ref>|sign=|source=}}

Packet switching allows delivery of [[variable bit rate]] data streams, realized as sequences of short messages in fixed format, i.e. ''[[Network packet|packets]]'', over a [[computer network]] which allocates transmission resources as needed using [[statistical multiplexing]] or [[dynamic bandwidth allocation]] techniques. As they traverse [[networking hardware]], such as switches and [[Router (computing)|routers]], packets are received, buffered, queued, and retransmitted ([[store and forward|stored and forwarded]]), resulting in variable latency and [[throughput]] depending on the link capacity and the traffic load on the network. Packets are normally forwarded by intermediate network nodes asynchronously using [[first-in, first-out]] buffering, but may be forwarded according to some scheduling discipline for [[fair queuing]], [[traffic shaping]], or for differentiated or guaranteed [[quality of service]], such as [[weighted fair queuing]] or [[leaky bucket]]. Packet-based communication may be implemented with or without intermediate forwarding nodes (switches and routers). In case of a shared physical medium (such as radio or [[10BASE5]]), the packets may be delivered according to a [[multiple access]] scheme.

Packet switching contrasts with another principal networking paradigm, [[circuit switching]], a method which pre-allocates dedicated network bandwidth specifically for each communication session, each having a constant bit rate and latency between nodes. In cases of billable services, such as [[cellular communication]] services, circuit switching is characterized by a fee per unit of connection time, even when no data is transferred, while packet switching may be characterized by a fee per unit of information transmitted, such as characters, packets, or messages.

A packet switch has four components: input ports, output ports, routing processor, and switching fabric.<ref>{{Cite book|last1=Forouzan|first1=Behrouz A.|url=https://books.google.com/books?id=bwUNZvJbEeQC&q=A+packet+switch+has+four+components:+input+ports,+output+ports,+routing+processor,+and+switching+fabric&pg=PA232|title=Data Communications and Networking|last2=Fegan|first2=Sophia Chung|date=2007|publisher=Huga Media|isbn=978-0-07-296775-3|language=en}}</ref>

==History==
{{Further|History of the Internet|Protocol Wars}}
{{See also|Datagram#History}}<!--consider merging overlapping content at some point-->

=== Invention and development ===
[[File:The idea of the data packet (Baran, 1964)-en.svg|thumb|The "message block", designed by Paul Baran in 1962 and refined in 1964, is the first proposal of a [[data packet]].<ref name=":1" /><ref name=":10" />]]
[[File:Packet-switching cost performance trends, 1960-1980.svg|thumb|Packet-switching cost performance trends, 1960-1980.<ref name="Roberts 141–172">{{Citation |last=Roberts |first=L. |title=The arpanet and computer networks |date=1988 |work=A history of personal workstations |pages=141–172 |url=https://doi.org/10.1145/61975.66916 |access-date=2023-11-30 |place=New York, NY, USA |publisher=Association for Computing Machinery |doi=10.1145/61975.66916 |isbn=978-0-201-11259-7}}</ref>]]

The concept of switching small blocks of data was first invented independently by [[Paul Baran]] at the [[RAND Corporation]] during the early 1960s in the US and [[Donald Davies]] at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL) in the UK in 1965.<ref name=":16">{{Cite news |title=The real story of how the Internet became so vulnerable |url=http://www.washingtonpost.com/sf/business/2015/05/30/net-of-insecurity-part-1/ |url-status=dead |archive-url=https://web.archive.org/web/20150530231409/http://www.washingtonpost.com/sf/business/2015/05/30/net-of-insecurity-part-1/ |archive-date=2015-05-30 |access-date=2020-02-18 |newspaper=Washington Post |language=en-US |quote=Historians credit seminal insights to Welsh scientist Donald W. Davies and American engineer Paul Baran}}</ref><ref name="Pelkeyp42">{{cite book |last1=Pelkey |first1=James L. |url=https://www.morganclaypoolpublishers.com/catalog_Orig/samples/9781450397292_sample.pdf |title=Circuits, Packets, and Protocols: Entrepreneurs and Computer Communications, 1968-1988 |last2=Russell |first2=Andrew L. |last3=Robbins |first3=Loring G. |date=2022 |publisher=Morgan & Claypool |isbn=978-1-4503-9729-2 |page=4 |quote="Paul Baran, an engineer celebrated as the co-inventor (along with Donald Davies) of the packet switching technology that is the foundation of digital networks" |archive-date=2024-04-23 |access-date=2023-11-22 |archive-url=https://web.archive.org/web/20240423181017/https://www.morganclaypoolpublishers.com/catalog_Orig/samples/9781450397292_sample.pdf |url-status=dead }}</ref><ref name="NIHF2007">{{cite web|title=Inductee Details - Paul Baran|url=https://www.invent.org/inductees/paul-baran|publisher=National Inventors Hall of Fame|access-date=6 September 2017|postscript=none}}; {{cite web|title=Inductee Details - Donald Watts Davies|url=https://www.invent.org/inductees/donald-watts-davies|publisher=National Inventors Hall of Fame|access-date=6 September 2017}}</ref><ref>{{Cite journal |last=Edmondson-Yurkanan |first=Chris |date=2007 |title=SIGCOMM's archaeological journey into networking's past |url=https://dl.acm.org/doi/10.1145/1230819.1230840 |journal=Communications of the ACM |language=en |volume=50 |issue=5 |pages=63–68 |doi=10.1145/1230819.1230840 |issn=0001-0782 |quote=The 1960 challenge was to build a network such that a significant subset of the network could survive a military attack. [Baran] told us he knew he could design a solution once he realized that, 'given redundant paths, the reliability of the net work could be greater than the reliability of the parts.' ... In his first draft dated Nov. 10, 1965, Davies forecast today’s 'killer app' for his new communication service: 'The greatest traffic could only come if the public used this means for everyday purposes such as shopping... People sending enquiries and placing orders for goods of all kinds will make up a large section of the traffic... Business use of the telephone may be reduced by the growth of the kind of service we contemplate.'|url-access=subscription }}</ref>

In the late 1950s, the [[US Air Force]] established a [[wide area network]] for the [[Semi-Automatic Ground Environment]] (SAGE) radar defense system. Recognizing vulnerabilities in this network, the Air Force sought a system that might survive a [[nuclear attack]] to enable a response, thus diminishing the attractiveness of the first strike advantage by enemies (see [[Mutual assured destruction]]). In the early 1960s, Baran invented the concept of ''distributed adaptive message block switching'' in support of the Air Force initiative.<ref name=":17" /><ref>{{Cite journal |last=Baran |first=Paul |date=May 27, 1960 |title=Reliable Digital Communications Using Unreliable Network Repeater Nodes |url=http://www.rand.org/content/dam/rand/pubs/papers/2008/P1995.pdf |url-status=live |journal=The RAND Corporation |page=1 |archive-url=https://ghostarchive.org/archive/20221010/http://www.rand.org/content/dam/rand/pubs/papers/2008/P1995.pdf |archive-date=2022-10-10 |access-date=July 7, 2016}}</ref> The concept was first presented to the Air Force in the summer of 1961 as briefing B-265,<ref name="steward">{{cite web |last=Stewart |first=Bill |date=2000-01-07 |title=Paul Baran Invents Packet Switching |url=http://www.livinginternet.com/i/ii_rand.htm |access-date=2008-05-08 |work=Living Internet}}</ref> later published as RAND report P-2626 in 1962,<ref name=":1">{{cite web|url=http://www.rand.org/pubs/papers/P2626/|title=RAND Paper P-2626|last= Baran|first=Paul|year=1962}}</ref> and finally in report RM 3420 in 1964.<ref name=":10">{{cite web|url=http://www.rand.org/pubs/research_memoranda/RM3420/index.html|title=On Distributed Communications|date=January 1964|last1=Baran|first1=Paul}}</ref> The reports describe a general architecture for a large-scale, distributed, survivable communications network. The proposal was composed of three key ideas: use of a [[decentralized]] network with multiple paths between any two points; dividing user messages into ''message blocks;'' and delivery of these messages by [[store and forward]] switching.<ref name=":17">{{Cite journal|last=Baran|first=Paul|date=2002|title=The beginnings of packet switching: some underlying concepts|url=http://web.cs.ucla.edu/~lixia/papers/Baran2002.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://web.cs.ucla.edu/~lixia/papers/Baran2002.pdf |archive-date=2022-10-10 |url-status=live|journal=IEEE Communications Magazine|language=en|volume=40|issue=7|pages=42–48|doi=10.1109/MCOM.2002.1018006|bibcode=2002IComM..40g..42B |issn=0163-6804|quote=Essentially all the work was defined by 1961, and fleshed out and put into formal written form in 1962. The idea of hot potato routing dates from late 1960.}}</ref><ref>{{Cite web |title=Paul Baran and the Origins of the Internet |url=https://www.rand.org/about/history/baran.html |access-date=2020-02-15 |website=RAND Corporation |language=en}}</ref> Baran's network design was focused on [[digital communication]] of voice messages using hardware switches that were low-cost electronics.<ref name="Pelkey6.1a">{{Cite book |last=Pelkey |first=James L. |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968–1988 |chapter=6.1 The Communications Subnet: BBN 1969 |quote=As Kahn recalls: ... Paul Baran’s contributions ... I also think Paul was motivated almost entirely by voice considerations. If you look at what he wrote, he was talking about switches that were low-cost electronics. The idea of putting powerful computers in these locations hadn’t quite occurred to him as being cost effective. So the idea of computer switches was missing. The whole notion of protocols didn’t exist at that time. And the idea of computer-to-computer communications was really a secondary concern. |chapter-url=https://historyofcomputercommunications.info/section/6.1/the-communications-subnet-bbn-1969/}}</ref><ref name=":5a">{{Cite book |last=Waldrop |first=M. Mitchell |url=https://books.google.com/books?id=eRnBEAAAQBAJ&pg=PT285 |title=The Dream Machine |date=2018 |publisher=Stripe Press |isbn=978-1-953953-36-0 |pages=286 |language=en |quote=Baran had put more emphasis on digital voice communications than on computer communications.}}</ref><ref>{{Cite journal |last=Kleinrock |first=L. |date=1978 |title=Principles and lessons in packet communications |journal=Proceedings of the IEEE |volume=66 |issue=11 |pages=1320–1329 |doi=10.1109/PROC.1978.11143 |issn=0018-9219 |quote=Paul Baran ... focused on the routing procedures and on the survivability of distributed communication systems in a hostile  environment, but did not concentrate on the need for resource sharing in its form as we now understand it; indeed, the concept of a software switch was not present in his work.}}</ref> The ideas were not entirely original to Baran and the task to design a store and forward type of network was formulated by Baran's boss at RAND.<ref name=":25" />

[[Christopher Strachey]], who became [[University of Oxford|Oxford University's]] first Professor of Computation, filed a [[patent application]] in the United Kingdom for [[time-sharing]] in February 1959.<ref>{{Cite web |title=Computer Pioneers - Christopher Strachey |url=https://history.computer.org/pioneers/strachey.html |access-date=2020-01-23 |website=history.computer.org}}</ref><ref name=":132">{{Cite web |title=Computer - Time-sharing, Minicomputers, Multitasking |url=https://www.britannica.com/technology/computer/Time-sharing-and-minicomputers |access-date=2023-07-23 |website=Britannica |language=en}}</ref> In June that year, he gave a paper "Time Sharing in Large Fast Computers" at the [[International Federation for Information Processing#History|UNESCO Information Processing Conference]] in Paris where he passed the concept on to [[J. C. R. Licklider]].<ref name="ctsspg">{{cite book |last=Corbató |first=F. J. |url=http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf |title=The Compatible Time-Sharing System: A Programmer's Guide |publisher=MIT Press |year=1963 |isbn=978-0-262-03008-3 |display-authors=etal}}. "the first paper on time-shared computers by C. Strachey at the June 1959 UNESCO Information Processing conference".</ref><ref>{{harvnb|Gillies|Cailliau|2000|page=13}}</ref> Licklider (along with [[John McCarthy (computer scientist)|John McCarthy]]) was instrumental in the development of time-sharing. After conversations with Licklider about time-sharing with remote computers in 1965,<ref name="Roberts1978" /><ref name=":15">{{cite web |last1=Roberts |first1=Dr. Lawrence G. |date=May 1995 |title=The ARPANET & Computer Networks |url=http://www.packet.cc/files/arpanet-computernet.html |url-status=dead |archive-url=https://web.archive.org/web/20160324032800/http://www.packet.cc/files/arpanet-computernet.html |archive-date=24 March 2016 |access-date=13 April 2016}}</ref> Davies independently invented a similar [[data communication]] concept.<ref>{{Cite book |last=Roberts |first=Gareth Ffowc |url=https://books.google.com/books?id=waCYEAAAQBAJ&pg=PA102 |title=For the Recorde: A History of Welsh Mathematical Greats |date=2022 |publisher=University of Wales Press |isbn=978-1-78683-917-6 |language=en |quote=Mathematicians had already developed methods of analysing traffic jams - 'queueing theory' ... - but it needed new a insight to solve the problem of how to avoid bottle-necks between computers.}}</ref> His insight was to use short messages in fixed format with high data transmission rates to achieve rapid communications.<ref>{{Cite web |last=Pelkey |first=James L. |date=May 27, 1988 |title=Interview of Donald Davies |url=http://archive.computerhistory.org/resources/access/text/2017/11/102738594-05-01-acc.pdf}}</ref> He went on to develop a more advanced design for a hierarchical, high-speed [[computer network]] including [[Router (computing)|interface computers]] and [[communication protocol]]s.<ref name=":21">{{Cite web |last=Davies |first=D. W. |date=1966 |title=Proposal for a Digital Communication Network |url=https://www.dcs.gla.ac.uk/~wpc/grcs/Davies05.pdf |quote=all users of the network will provide themselves with some kind of error control ... Computer developments in the distant future might result in one type of network being able to carry speech and digital messages efficiently.}}</ref><ref>{{Citation |last1=Scantlebury |first1=R. A. |title=A Protocol for Use in the NPL Data Communications Network |date=April 1967 |publisher=Private papers |last2=Bartlett |first2=K. A.}}</ref><ref name=":5">{{cite conference |last1=Davies |first1=Donald |last2=Bartlett |first2=Keith |last3=Scantlebury |first3=Roger |last4=Wilkinson |first4=Peter |date=October 1967 |title=A Digital Communication Network for Computers Giving Rapid Response at remote Terminals |url=https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |conference=ACM Symposium on Operating Systems Principles |archive-url=https://ghostarchive.org/archive/20221010/https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |archive-date=2022-10-10 |access-date=2020-09-15 |url-status=live}}</ref> He coined the term ''packet switching'', and proposed building a commercial nationwide data network in the UK.<ref>{{Cite book |last=Yates |first=David M. |url=https://books.google.com/books?id=ToMfAQAAIAAJ&q=%22proposed+national+packet-switched+network%22 |title=Turing's Legacy: A History of Computing at the National Physical Laboratory 1945-1995 |date=1997 |publisher=National Museum of Science and Industry |isbn=978-0-901805-94-2 |page=130 |language=en}}</ref><ref>{{Citation |last= Davies |first= D. W. |author-link= Donald Davies |title= Oral History 189: D. W. Davies interviewed by Martin Campbell-Kelly at the National Physical Laboratory |publisher= Charles Babbage Institute University of Minnesota, Minneapolis |date= 17 March 1986 |url= http://conservancy.umn.edu/handle/107241 |access-date= 21 July 2014 |archive-url= https://web.archive.org/web/20140729025914/http://conservancy.umn.edu/handle/107241 |archive-date= 29 July 2014 |url-status= dead }}</ref> He gave a talk on the proposal in 1966, after which a person from the [[Ministry of Defence (United Kingdom)|Ministry of Defence]] (MoD) told him about Baran's work.<ref>{{Cite web |title=UK National Physical Laboratories, Donald Davies |url=https://www.livinginternet.com/i/ii_npl.htm |access-date=2024-06-05 |website=LivingInternet |language=en-US}}</ref>

[[Roger Scantlebury]], a member of Davies' team, presented their work (and referenced that of Baran) at the October 1967 [[Symposium on Operating Systems Principles]] (SOSP).<ref name=":5" /><ref>{{Cite book |last1=Hafner |first1=Katie |url=http://archive.org/details/wherewizardsstay00haf_vgj |title=Where wizards stay up late: the origins of the Internet |last2=Lyon |first2=Matthew |date=1996 |publisher=Simon & Schuster |others=Internet Archive |isbn=978-0-684-81201-4 |pages=76–78 |quote=Roger Scantlebury ... from Donald Davies' team ... presented a detailed design study for a packet switched network. It was the first Roberts had heard of it. ... Roberts also learned from Scantlebury, for the first time, of the work that had been done by Paul Baran at RAND a few years earlier.}}</ref><ref name="Moschovitisp58-9">{{harvnb|Moschovitis|1999|p=[https://archive.org/details/historyofinterne0000unse/page/58/mode/2up 58-9]}} More significantly, Roger Scantlebury ... presents the design for a packet-switched network. This is the first Roberts and Taylor have heard of packet switching, a concept that appears to be a promising receipe for transmitting data through the ARPAnet.</ref><ref name="C. Hempstead, W. Worthington">{{cite book |url=https://archive.org/details/EncyclopediaOf20thCenturyTechnologyAZMalestrom/page/n623/mode/2up |title=Encyclopedia of 20th-Century Technology |publisher=Routledge |year=2005 |isbn=9781135455514 |editor1-last=Hempstead |editor1-first=C. |volume=1, A-L |pages=574 |quote=It was a seminal meeting as the NPL proposal illustrated how the communications for such a resource-sharing computer network could be realized. |editor2-last=Worthington |editor2-first=W.}}</ref><ref>{{Cite web |title=On packet switching |url=https://www.nethistory.info/Archives/packets.html |access-date=2024-01-08 |website=Net History |quote=[Scantlebury said] We referenced Baran's paper in our 1967 Gatlinburg ACM paper. You  will find it in the References. Therefore I am sure that we introduced Baran's work to Larry (and hence the BBN guys).}}</ref> At the conference, Scantlebury proposed packet switching for use in the [[ARPANET]] and persuaded [[Lawrence Roberts (scientist)|Larry Roberts]] the economics were favorable to [[message switching]].<ref name=":18">{{cite book |last1=Naughton |first1=John |url=https://books.google.com/books?id=bbonCgAAQBAJ&q=they+lacked+one+vital+ingredient |title=A Brief History of the Future: The origins of the Internet |date=2015 |publisher=Hachette |isbn=978-1474602778 |quote=they lacked one vital ingredient. Since none of them had heard of Paul Baran they had no serious idea of how to make the system work. And it took an English outfit to tell them. ... Larry Roberts paper was the first public presentation of the ARPANET concept as conceived with the aid of Wesley Clark ... Looking at it now, Roberts paper seems extraordinarily, well, vague.}}</ref><ref name=":5b">{{Cite book |last=Waldrop |first=M. Mitchell |url=https://books.google.com/books?id=eRnBEAAAQBAJ&pg=PT285 |title=The Dream Machine |date=2018 |publisher=Stripe Press |isbn=978-1-953953-36-0 |pages=285–6 |language=en |quote=Scantlebury and his companions from the NPL group were happy to sit up with Roberts all that night, sharing technical details and arguing over the finer points.}}</ref><ref name="Abbate2000-2" /><ref>{{cite web |title=Oral-History:Donald Davies & Derek Barber |url=http://ethw.org/Oral-History:Donald_Davies_%26_Derek_Barber |access-date=13 April 2016 |quote=the ARPA network is being implemented using existing telegraphic techniques simply because the type of network we describe does not exist. It appears that the ideas in the NPL paper at this moment are more advanced than any proposed in the USA}}</ref><ref>{{cite journal |last1=Barber |first1=Derek |date=Spring 1993 |title=The Origins of Packet Switching |url=http://www.cs.man.ac.uk/CCS/res/res05.htm#f |journal=The Bulletin of the Computer Conservation Society |issue=5 |issn=0958-7403 |access-date=6 September 2017 |quote=Roger actually convinced Larry that what he was talking about was all wrong and that the way that NPL were proposing to do it was right. I've got some notes that say that first Larry was sceptical but several of the others there sided with Roger and eventually Larry was overwhelmed by the numbers.}}</ref><ref>{{Cite journal |last=Needham |first=Roger M. |date=2002-12-01 |title=Donald Watts Davies, C.B.E. 7 June 1924 – 28 May 2000 |url=https://royalsocietypublishing.org/doi/10.1098/rsbm.2002.0006 |journal=Biographical Memoirs of Fellows of the Royal Society |volume=48 |pages=87–96 |doi=10.1098/rsbm.2002.0006 |s2cid=72835589 |quote=Larry Roberts presented a paper on early ideas for what was to become ARPAnet. This was based on a store-and-forward method for entire messages, but as a result of that meeting the NPL work helped to convince Roberts that packet switching was the way forward.|url-access=subscription }}</ref> Davies had chosen some of the same parameters for his original network design as did Baran, such as a packet size of 1024 bits. To deal with packet permutations (due to dynamically updated route preferences) and [[datagram]] losses (unavoidable when fast sources send to a slow destinations), he assumed that "all users of the network will provide themselves with some kind of error control",<ref name=":5" /> thus inventing what came to be known as the [[end-to-end principle]]. Davies proposed that a local-area network should be built at the laboratory to serve the needs of NPL and prove the feasibility of packet switching. After a [[pilot experiment]] in early 1969,<ref name=":72">{{Cite conference |last1=Rayner |first1=David |last2=Barber |first2=Derek |last3=Scantlebury |first3=Roger |last4=Wilkinson |first4=Peter |date=2001 |title=NPL, Packet Switching and the Internet |url=http://www.topquark.co.uk/conf/IAP2001.html |conference=Symposium of the Institution of Analysts & Programmers 2001 |access-date=2024-06-13 |quote=The system first went 'live' early in 1969 |website=|archive-url=https://web.archive.org/web/20030807200346/http://www.topquark.co.uk/conf/IAP2001.html |archive-date=2003-08-07 }}</ref><ref name=":22">{{Cite journal |last1=John S |first1=Quarterman |last2=Josiah C |first2=Hoskins |date=1986 |title=Notable computer networks |journal=Communications of the ACM |language=EN |volume=29 |issue=10 |pages=932–971 |doi=10.1145/6617.6618 |s2cid=25341056 |quote=The first packet-switching network was implemented at the National Physical Laboratories in the United Kingdom. It was quickly followed by the ARPANET in 1969. |doi-access=free}}</ref><ref name="Haughney Dare-Bryan" /><ref name="Hempstead2005">{{cite book |author1=C. Hempstead |url=https://archive.org/details/EncyclopediaOf20thCenturyTechnologyAZMalestrom/page/n621/mode/2up?q=packet+switching |title=Encyclopedia of 20th-Century Technology |author2=W. Worthington |date=2005 |publisher=[[Routledge]] |isbn=9781135455514 |pages=573–5}}</ref> the [[NPL Data Communications Network]] began service in 1970.<ref name=":3b">{{Cite journal |last=Campbell-Kelly |first=Martin |date=1987 |title=Data Communications at the National Physical Laboratory (1965-1975) |url=https://archive.org/details/DataCommunicationsAtTheNationalPhysicalLaboratory |journal=Annals of the History of Computing |language=en |volume=9 |issue=3/4 |pages=221–247 |doi=10.1109/MAHC.1987.10023 |s2cid=8172150}}</ref> Davies was invited to Japan to give a series of lectures on packet switching.<ref name="frs">{{Cite journal |last1=Needham |first1=R. M. |author-link=Roger Needham |year=2002 |title=Donald Watts Davies, C.B.E. 7 June 1924 – 28 May 2000 |journal=[[Biographical Memoirs of Fellows of the Royal Society]] |volume=48 |pages=87–96 |doi=10.1098/rsbm.2002.0006 |s2cid=72835589 |quote=The 1967 Gatlinburg paper was influential on the development of ARPAnet, which might otherwise have been built with less extensible technology. ... Davies was invited to Japan to lecture on packet switching.}}</ref> The NPL team carried out [[simulation]] work on datagrams and [[Network congestion|congestion]] in networks on a scale to provide data communication across the United Kingdom.<ref name="Hempstead2005" /><ref name=":82">{{Cite thesis |last=Clarke |first=Peter |title=Packet and circuit-switched data networks |date=1982 |degree=PhD |publisher=Department of Electrical Engineering, Imperial College of Science and Technology, University of London |url=https://spiral.imperial.ac.uk/bitstream/10044/1/35864/2/Clarke-PN-1982-PhD-Thesis.pdf |archive-date=2022-08-03 |access-date=2024-01-21 |archive-url=https://web.archive.org/web/20220803035935/https://spiral.imperial.ac.uk/bitstream/10044/1/35864/2/Clarke-PN-1982-PhD-Thesis.pdf |url-status=dead }} "As well as the packet switched network actually built at NPL for communication between their local computing facilities, some simulation experiments have been performed on larger networks. A summary of this work is reported in [69]. The work was carried out to investigate networks of a size capable of providing data communications facilities to most of the U.K. ... Experiments were then carried out using a method of flow control devised by Davies [70] called 'isarithmic' flow control. ... The simulation work carried out at NPL has, in many respects, been more realistic than most of the ARPA network theoretical studies."</ref><ref name="Pelkey">{{cite book |last=Pelkey |first=James |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968-1988 |chapter=6.3 CYCLADES Network and Louis Pouzin 1971-1972 |access-date=2020-02-03 |chapter-url=http://www.historyofcomputercommunications.info/Book/6/6.3-CYCLADESNetworkLouisPouzin1-72.html |archive-url=https://web.archive.org/web/20210617093154/https://www.historyofcomputercommunications.info/Book/6/6.3-CYCLADESNetworkLouisPouzin1-72.html |archive-date=2021-06-17 |url-status=dead}}</ref><ref name="MCK">{{cite journal |last=Campbell-Kelly |first=Martin |date=Autumn 2008 |title=Pioneer Profiles: Donald Davies |url=http://www.computerconservationsociety.org/resurrection/res44.htm |journal=Computer Resurrection |issn=0958-7403 |number=44}}</ref><ref>{{Cite conference |last=Wilkinson |first=Peter|date=2001 |title=NPL Development of Packet Switching |url=http://www.topquark.co.uk/conf/IAP2001.html |archive-url=https://web.archive.org/web/20030807200346/http://www.topquark.co.uk/conf/IAP2001.html |conference=Symposium of the Institution of Analysts & Programmers 2001 |access-date=2024-06-13 |archive-date=2003-08-07 |quote=The feasibility studies continued with an attempt to apply queuing theory to study overall network performance. This proved to be intractable so we quickly turned to simulation.}}</ref>

[[Lawrence Roberts (scientist)|Larry Roberts]] made the key decisions in the [[request for proposal]] to build the [[ARPANET]].<ref name=":4">{{Cite news |last=Hafner |first=Katie |date=2018-12-30 |title=Lawrence Roberts, Who Helped Design Internet's Precursor, Dies at 81 |url=https://www.nytimes.com/2018/12/30/obituaries/lawrence-g-roberts-dies-at-81.html |access-date=2020-02-20 |work=The New York Times |issn=0362-4331 |quote=He decided to use packet switching as the underlying technology of the Arpanet; it remains central to the function of the internet. And it was Dr. Roberts's decision to build a network that distributed control of the network across multiple computers. Distributed networking remains another foundation of today's internet.}}</ref> Roberts met Baran in February 1967, but did not discuss networks.<ref name=":5c">{{Cite book |last=Waldrop |first=M. Mitchell |url=https://books.google.com/books?id=eRnBEAAAQBAJ&pg=PT285 |title=The Dream Machine |date=2018 |publisher=Stripe Press |isbn=978-1-953953-36-0 |pages=285–6 |language=en |quote=Oops. Roberts knew Baran slightly and had in fact had lunch with him during a visit to RAND the previous February. But he certainly didn't remember any discussion of networks. How could he have missed something like that?}}</ref><ref>{{Cite web |last=O'Neill |first=Judy |date=5 March 1990 |title=An Interview with PAUL BARAN |url=https://conservancy.umn.edu/bitstream/handle/11299/107101/oh182pb.pdf?sequence=1&isAllowed=y |page=37 |quote=On Tuesday, 28 February 1967 I find a notation on my calendar for 12:00 noon Dr. L. Roberts.}}</ref> He asked [[Frank Westervelt]] to explore the questions of message size and contents for the network, and to write a position paper on the intercomputer communication protocol including “conventions for character and block transmission, error checking and re transmission, and computer and user identification."<ref name=":242">{{cite web |last=Pelkey |first=James |title=4.7 Planning the ARPANET: 1967-1968 in Chapter 4 - Networking: Vision and Packet Switching 1959 - 1968 |url=https://historyofcomputercommunications.info/section/4.7/planning-the-arpanet-1967-1968/ |url-status=dead |archive-url=https://web.archive.org/web/20221223230647/https://historyofcomputercommunications.info/section/4.7/planning-the-arpanet-1967-1968/ |archive-date=December 23, 2022 |access-date=May 9, 2023 |work=The History of Computer Communications}}</ref> Roberts revised his initial design, which was to connect the [[host computer]]s directly, to incorporate [[Wesley A. Clark|Wesley Clark's]] idea to use [[Interface Message Processor]]s (IMPs) to create a [[message switching]] network, which he presented at SOSP.<ref>{{Cite web |last=Press |first=Gil |date=January 2, 2015 |title=A Very Short History Of The Internet And The Web |url=https://www.forbes.com/sites/gilpress/2015/01/02/a-very-short-history-of-the-internet-and-the-web-2/ |url-status=live |archive-url=https://web.archive.org/web/20150109145400/https://www.forbes.com/sites/gilpress/2015/01/02/a-very-short-history-of-the-internet-and-the-web-2/ |archive-date=January 9, 2015 |access-date=2020-02-07 |website=Forbes |language=en |quote=Roberts' proposal that all host computers would connect to one another directly ... was not endorsed ... Wesley Clark ... suggested to Roberts that the network be managed by identical small computers, each attached to a host computer. Accepting the idea, Roberts named the small computers dedicated to network administration 'Interface Message Processors' (IMPs), which later evolved into today's routers.}}</ref><ref>{{Citation |title=SRI Project 5890-1; Networking (Reports on Meetings) |url=https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/EngelbartPapers/B1_F20_CompuMtg.html |year=1967 |access-date=2020-02-15 |archive-url=https://web.archive.org/web/20200202062940/https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/EngelbartPapers/B1_F20_CompuMtg.html |publisher=Stanford University |quote=W. Clark's message switching proposal (appended to Taylor's letter of April 24, 1967 to Engelbart)were reviewed. |archive-date=February 2, 2020}}</ref><ref name=":19">{{Cite book |last=Roberts |first=Lawrence |title=Multiple Computer Networks and Intercomputer Communications |date=1967 |pages=3.1–3.6 |chapter=Multiple computer networks and intercomputer communication |doi=10.1145/800001.811680 |quote=Thus the set of IMP's, plus the telephone lines and data sets would constitute a message switching network |chapter-url=https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/arpanet.pdf |s2cid=17409102}}</ref><ref name=":20">{{Cite book |last1=Tanenbaum |first1=Andrew S. |url=https://csc-knu.github.io/sys-prog/books/Andrew%20S.%20Tanenbaum%20-%20Computer%20Networks.pdf |title=Computer networks |last2=Wetherall |first2=David |date=2011 |publisher=Prentice Hall |isbn=978-0-13-212695-3 |edition=5th |location=Boston Amsterdam |page=57 |quote=Roberts bought the idea and presented a some what vague paper about it at the ACM SIGOPS Symposium on Operating System Principles held in Gatlinburg, Tennessee in late 1967}}</ref> Roberts was known for making decisions quickly.<ref name=":5d">{{Cite book |last=Waldrop |first=M. Mitchell |url=https://books.google.com/books?id=eRnBEAAAQBAJ&pg=PT279 |title=The Dream Machine |date=2018 |publisher=Stripe Press |isbn=978-1-953953-36-0 |pages=279, 284–5 |language=en |quote=Roberts was already becoming known as the fastest man in the Pentagon. ... And not for nothing was Larry Roberts known as the fastest man in the Pentagon. By the time they got to the airport, the decision had been made .... Once again, the fastest man in the Pentagon made his decision without hesitation}}</ref> Immediately after SOSP, he incorporated Davies' and Baran's concepts and designs for packet switching to enable the data communications on the network.<ref name="Abbate2000-2">{{cite book |last1=Abbate |first1=Jane |author-link=Janet Abbate |url=https://books.google.com/books?id=E2BdY6WQo4AC&q=packet+switching&pg=PA125 |title=Inventing the Internet |date=2000 |publisher=MIT Press |isbn=978-0262261333 |pages=37–8, 58–9 |quote=The NPL group influenced a number of American computer scientists in favor of the new technique, and they adopted Davies's term "packet switching" to refer to this type of network. Roberts also adopted some specific aspects of the NPL design.}}</ref><ref name=":6">{{cite web |title=Shapiro: Computer Network Meeting of October 9–10, 1967 |url=https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/Archive/Post68/ARPANETMeeting1167.html |archive-url=https://web.archive.org/web/20150627133802/https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/Archive/Post68/ARPANETMeeting1167.html |archive-date=27 June 2015 |website=stanford.edu}}</ref><ref>{{Cite web |title=Computer Pioneers - Donald W. Davies |url=https://history.computer.org/pioneers/davies.html |access-date=2020-02-20 |website=IEEE Computer Society |quote=In 1965, Davies pioneered new concepts for computer communications in a form to which he gave the name "packet switching." ... The design of the ARPA network (ArpaNet) was entirely changed to adopt this technique. |postscript=none}}</ref><ref>[http://www.internethalloffame.org/inductees/donald-davies "Pioneer: Donald Davies"], Internet Hall of Fame "America’s Advanced Research Project Agency (ARPA), and the ARPANET received his network design enthusiastically and the NPL local network became the first two computer networks in the world using the technique."</ref>

A contemporary of Roberts' from [[MIT]], [[Leonard Kleinrock]] had researched the application of [[queueing theory]] in the field of [[message switching]] for his doctoral dissertation in 1961–62 and published it as a book in 1964.<ref>{{cite book |last1=Isaacson |first1=Walter |url=https://books.google.com/books?id=4V9koAEACAAJ&pg=PA245 |title=The Innovators: How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution |date=2014 |publisher=Simon and Schuster |isbn=9781476708690 |page=246}}</ref> Davies, in his 1966 paper on packet switching,<ref name=":21" /> applied Kleinorck's techniques to show that "there is an ample margin between the estimated performance of the [packet-switched] system and the stated requirement" in terms of a satisfactory [[Response time (telecommunications)|response time]] for a human user.<ref>{{Cite web |last=Davies |first=D. W. |date=1966 |title=Proposal for a Digital Communication Network |url=https://www.dcs.gla.ac.uk/~wpc/grcs/Davies05.pdf |page=10, 16}}</ref> This addressed a key question about the viability of computer networking.<ref name=":92">{{cite tech report|last1=Heart|first1=F.|last2=McKenzie|first2=A.|last3=McQuillian|first3=J.|last4=Walden|first4=D.|url=https://web.archive.org/web/20230527095942/https://walden-family.com/bbn/arpanet-completion-report.pdf|title=Arpanet Completion Report|publisher=Bolt, Beranek and Newman|location=Burlington, MA|date=January 4, 1978}} pp. III-40-1</ref> Larry Roberts brought Kleinrock into the ARPANET project informally in early 1967.<ref>{{Cite web |title=SRI Project 5890-1; Networking (Reports on Meetings). [1967] |url=http://sloan.stanford.edu/mousesite/EngelbartPapers/B1_F20_CompuMtg.html |access-date=2020-02-15 |website=web.stanford.edu|archive-url=https://web.archive.org/web/20110810063347/http://sloan.stanford.edu/mousesite/EngelbartPapers/B1_F20_CompuMtg.html |archive-date=2011-08-10 }}</ref> Roberts and Taylor recognized the issue of response time was important, but did not apply Kleinrock's methods to assess this and based their design on a [[store-and-forward]] system that was not intended for [[real-time computing]].<ref>{{harvnb|Hafner|Lyon|1996}}</ref> After SOSP, and after Roberts' direction to use packet switching,<ref name=":6" /> Kleinrock sought input from Baran and proposed to retain Baran and RAND as advisors.<ref name="Abbate2000-3">{{cite book |last1=Abbate |first1=Janet |url=https://books.google.com/books?id=9BfZxFZpElwC&pg=PA37 |title=Inventing the Internet |publisher=[[MIT Press]] |year=2000 |isbn=978-0-2625-1115-5 |location=Cambridge, MA |pages=39, 57–58 |quote=Baran proposed a "distributed adaptive message-block network" [in the early 1960s] ... Roberts recruited Baran to advise the ARPANET planning group on distributed communications and packet switching. ... Roberts awarded a contract to Leonard Kleinrock of UCLA to create theoretical models of the network and to analyze its actual performance.}}</ref><ref>{{citation |title=Summary of ARPA ad hoc meeting |date=November 3, 1967 |url=https://archive.org/details/SummaryOfArpaAdHocMeeting/page/n1/mode/2up |quote=We propose that a working group of approximately four people devote some concentrated effort in the near future in defining the IMP precisely. This group would interact with the larger group from the earlier meetings from time to time. Tentatively we think that the core of this investigatory group would be Bhushan (MIT), Kleinrock (UCLA), Shapiro (SRI) and Westervelt (University of Michigan), along with a kibitzer's group, consisting of such people as Baran (Rand), Boehm (Rand), Culler (UCSB) and Roberts (ARPA).}}</ref><ref>{{citation |author=Judy O'Neill |title=Oral history interview with Paul Baran |date=1990 |url=https://conservancy.umn.edu/handle/11299/107101 |publisher=Charles Babbage Institute |hdl=11299/107101 |quote=BARAN: On Tuesday, 31 October 1967 I see a notation 9:30 AM to 2:00 PM for ARPA's (Elmer) Shapiro, (Barry) Boehm, (Len) Kleinrock, ARPA Network. On Monday, 13 November 1967 I see the following: Larry Roberts to abt (about?) lunch (time?). Art Bushkin = 1:00 PM. Here. Larry Roberts IMP Committee. On Thursday, 16 November 1967 I see 7 PM Kleinrock, UCLA - IMP Meeting.}}</ref> The ARPANET working group assigned Kleinrock responsibility to prepare a report on software for the IMP.<ref>{{citation |title=Meeting of the ARPA Computer Network Working Group at UCLA |date=November 16, 1967 |url=https://archive.org/details/MeetingOfTheArpaComputerNetworkWorkingGroupAtUcla}}</ref> In 1968, Roberts awarded Kleinrock a contract to establish a Network Measurement Center (NMC) at [[UCLA]] to measure and model the performance of packet switching in the ARPANET.<ref name="Abbate2000-3" /> 

[[Bolt Beranek & Newman]] (BBN) won the contract to build the network. Designed principally by [[Bob Kahn]],<ref name="Hafner1">{{harvnb|Hafner|Lyon|1996|pp=[https://archive.org/details/wherewizardsstay00haf_vgj/page/116/mode/2up?q=kahn 116, 149]}}</ref><ref name="Pelkey6.1b">{{Cite book |last=Pelkey |first=James L. |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968–1988 |chapter=6.1 The Communications Subnet: BBN 1969 |quote=Kahn, the principal architect |chapter-url=https://historyofcomputercommunications.info/section/6.1/the-communications-subnet-bbn-1969/}}</ref> it was the first wide-area packet-switched network with distributed control.<ref name=":4" /> The BBN "IMP Guys" independently developed significant aspects of the network's internal operation, including the routing algorithm, flow control, software design, and network control.<ref name=":2A3">{{cite journal |last1=Roberts |first1=Lawrence G. |date=November 1978 |title=The Evolution of Packet Switching |url=http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf |url-status=dead |journal=IEEE Invited Paper |archive-url=https://web.archive.org/web/20181231092936/http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf |archive-date=31 December 2018 |access-date=September 10, 2017 |quote=Significant aspects of the network's internal operation, such as routing, flow control, software design, and network control were developed by a BBN team consisting of Frank Heart, Robert Kahn, Severo Omstein, William Crowther, and David Walden}}</ref><ref name="F.E. Froehlich, A. Kent">{{cite book |author=F.E. Froehlich, A. Kent |url=https://books.google.com/books?id=gaRBTHdUKmgC&pg=PA344 |title=The Froehlich/Kent Encyclopedia of Telecommunications: Volume 1 - Access Charges in the U.S.A. to Basics of Digital Communications |date=1990 |publisher=CRC Press |isbn=0824729005 |page=344 |quote=Although there was considerable technical interchange between the NPL group and those who designed and implemented the ARPANET, the NPL Data Network effort appears to have had little fundamental impact on the design of ARPANET. Such major aspects of the NPL Data Network design as the standard network interface, the routing algorithm, and the software structure of the switching node were largely ignored by the ARPANET designers. There is no doubt, however, that in many less fundamental ways the NPL Data Network had and effect on the design and evolution of the ARPANET.}}</ref> The UCLA NMC and the BBN team also investigated network congestion.<ref name="Hafner1" /><ref>{{IETF RFC|334}}</ref> The Network Working Group, led by [[Steve Crocker]], a graduate student of Kleinrock's at UCLA, developed the host-to-host protocol, the [[Network Control Program (ARPANET)|Network Control Program]], which was approved by Barry Wessler for ARPA,<ref>{{IETF RFC|53}}</ref> after he ordered certain more exotic elements to be dropped.<ref>{{cite tech report|last1=Heart|first1=F.|last2=McKenzie|first2=A.|last3=McQuillian|first3=J.|last4=Walden|first4=D.|url=https://web.archive.org/web/20230527095942/https://walden-family.com/bbn/arpanet-completion-report.pdf|title=Arpanet Completion Report|publisher=Bolt, Beranek and Newman|location=Burlington, MA|date=January 4, 1978|page=III-63}}</ref> In 1970, Kleinrock extended his earlier [[Analytics|analytic]] work on message switching to packet switching in the ARPANET.<ref name=":12">{{Cite thesis |last=Clarke |first=Peter |title=Packet and circuit-switched data networks |date=1982 |degree=PhD |publisher=Department of Electrical Engineering, Imperial College of Science and Technology, University of London |url=https://spiral.imperial.ac.uk/bitstream/10044/1/35864/2/Clarke-PN-1982-PhD-Thesis.pdf |archive-date=2022-08-03 |access-date=2024-01-21 |archive-url=https://web.archive.org/web/20220803035935/https://spiral.imperial.ac.uk/bitstream/10044/1/35864/2/Clarke-PN-1982-PhD-Thesis.pdf |url-status=dead }}  "Many of the theoretical studies of the performance and design of the ARPA Network were developments of earlier work by Kleinrock ... Although these works concerned message switching networks, they were the basis for a lot of the ARPA network investigations ... The intention of the work of Kleinrock [in 1961] was to analyse the performance of store and forward networks ... Kleinrock [in 1970] extended the theoretical approaches of [his 1961 work] to the early ARPA network."</ref> His work influenced the development of the ARPANET and packet-switched networks generally.<ref>{{Cite book |last=Abbate |first=Janet |url=https://archive.org/details/inventinginterne00jane/page/230/mode/2up?q=%22On+Kleinrock%27s+influence%22 |title=Inventing the Internet |date=1999 |publisher=MIT Press |others=Internet Archive |isbn=978-0-262-01172-3 |pages=230 |quote=On Kleinrock’s influence, see Frank, Kahn, and Kleinrock 1972, p. 265; Tanenbaum 1989, p. 631.}}</ref><ref name=":42">{{Cite book |last=Davies |first=Donald Watts |url=https://archive.org/details/computernetworks00davi/page/86/mode/2up?q=kleinrock+kleinrock%27s |title=Computer networks and their protocols |date=1979 |publisher=Wiley |others=Internet Archive |isbn=978-0-471-99750-4 |pages=See page refs highlighted at url}}</ref><ref>{{Cite journal |last=Kleinrock |first=L. |date=1978 |title=Principles and lessons in packet communications |journal=Proceedings of the IEEE |volume=66 |issue=11 |pages=1320–1329 |doi=10.1109/PROC.1978.11143 |issn=0018-9219}}</ref> 

The ARPANET was demonstrated at the [[International Conference on Computer Communications|International Conference on Computer Communication]] (ICCC) in Washington in October 1972.<ref name="Pelkey8.32">{{cite book |last=Pelkey |first=James |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968–1988 |chapter=8.3 CYCLADES Network and Louis Pouzin 1971–1972 |chapter-url=https://historyofcomputercommunications.info/section/8.3/CYCLADES-Network-and-Louis-Pouzin-1971-1972/}}</ref><ref name="Hafnerp2222">{{harvnb|Hafner|Lyon|1996|p=[https://archive.org/details/wherewizardsstay00haf_vgj/page/222/mode/2up 222]}}</ref> However, fundamental questions about the design of packet-switched networks remained.<ref name="Pelkey8.4b">{{cite book |last=Pelkey |first=James |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968–1988 |chapter=8.4 Transmission Control Protocol (TCP) 1973-1976 |quote=Arpanet had its deficiencies, however, for it was neither a true datagram network nor did it provide end-to-end error correction. |chapter-url=https://historyofcomputercommunications.info/section/8.4/transmission-control-protocol-(tcp)-1973-1976/}}</ref><ref>{{Cite book |last=Pouzin |first=Louis |chapter=An integrated approach to network protocols |date=May 1975 |title=Proceedings of the May 19-22, 1975, national computer conference and exposition on - AFIPS '75 |chapter-url=https://dl.acm.org/doi/10.1145/1499949.1500100 |publisher=Association for Computing Machinery |pages=701–707 |doi=10.1145/1499949.1500100 |isbn=978-1-4503-7919-9|s2cid=1689917 }}</ref><ref name=":2A" />

Roberts presented the idea of packet switching to communication industry professionals in the early 1970s. Before ARPANET was operating, they argued that the router buffers would quickly run out. After the ARPANET was operating, they argued packet switching would never be economic without the government subsidy. Baran had faced the same rejection and thus failed to convince the military into constructing a packet switching network in the 1960s.<ref name="Roberts 141–172"/>

The [[CYCLADES]] network was designed by [[Louis Pouzin]] in the early 1970s to study [[internetworking]].<ref name=":28">{{Cite book |last=Abbate |first=Janet |url=https://books.google.com/books?id=E2BdY6WQo4AC&pg=PA125 |title=Inventing the Internet |date=2000 |publisher=MIT Press |isbn=978-0-262-51115-5 |pages=124–127 |language=en |quote=In fact, CYCLADES, unlike ARPANET, had been explicitly designed to facilitate internetworking; it could, for instance, handle varying formats and varying levels of service |author-link=Janet Abbate}}</ref><ref name="Kim2005">{{cite book |last1=Kim |first1=Byung-Keun |url=https://books.google.com/books?id=lESrw3neDokC&pg=PA54 |title=Internationalising the Internet the Co-evolution of Influence and Technology |date=2005 |publisher=Edward Elgar |isbn=1845426754 |pages=51–55 |quote=In addition to the NPL Network and the ARPANET, CYCLADES, an academic and research experimental network, also played an important role in the development of computer networking technologies}}</ref><ref name=":7">{{Cite news |date=2013-11-30 |title=The internet's fifth man |newspaper=The Economist |url=https://www.economist.com/news/technology-quarterly/21590765-louis-pouzin-helped-create-internet-now-he-campaigning-ensure-its |access-date=2020-04-22 |issn=0013-0613 |quote=In the early 1970s Mr Pouzin created an innovative data network that linked locations in France, Italy and Britain. Its simplicity and efficiency pointed the way to a network that could connect not just dozens of machines, but millions of them. It captured the imagination of Dr Cerf and Dr Kahn, who included aspects of its design in the protocols that now power the internet.}}</ref> It was the first to implement the end-to-end principle of Davies, and make the host computers responsible for the reliable delivery of data on a packet-switched network, rather than this being a service of the network itself.<ref name="Bennett20092">{{cite web |last1=Bennett |first1=Richard |date=September 2009 |title=Designed for Change: End-to-End Arguments, Internet Innovation, and the Net Neutrality Debate |url=https://www.itif.org/files/2009-designed-for-change.pdf |access-date=11 September 2017 |publisher=Information Technology and Innovation Foundation |pages=7, 9, 11 |quote=Two significant packet networks preceded the TCP/IP Internet: ARPANET and CYCLADES. The designers of the Internet borrowed heavily from these systems, especially CYCLADES ... The first end-to-end research network was CYCLADES, designed by Louis Pouzin at IRIA in France with the support of BBN’s Dave Walden and Alex McKenzie and deployed beginning in 1972.}}</ref> His team was thus first to tackle the highly-complex problem of providing user applications with a reliable [[virtual circuit]] service while using a [[best-effort service]], an early contribution to what will be the [[Transmission Control Protocol]] (TCP).<ref>{{Cite book |last=Green |first=Lelia |url=https://www.worldcat.org/title/504280762 |title=The internet: an introduction to new media |date=2010 |publisher=Berg |isbn=978-1-84788-299-8 |series=Berg new media series |page=31 |oclc=504280762 |quote=The original ARPANET design had made data integrity part of the IMP's store-and-forward role, but Cyclades end-to-end protocol greatly simplified the packet switching operations of the network. ... The idea was to adopt several principles from Cyclades and invert the ARPANET model to minimise international differences.}}</ref>

[[Bob Metcalfe]] and others at [[Xerox PARC]] outlined the idea of [[Ethernet]] and the [[PARC Universal Packet]] (PUP) for internetworking.<ref name="Moschovitisp78-9">{{harvnb|Moschovitis|1999|p=[https://archive.org/details/historyofinterne0000unse/page/78/mode/2up 78-9]}}</ref>

In May 1974, [[Vint Cerf]] and [[Bob Kahn]] described the [[Transmission Control Program]], an internetworking [[Communication protocol|protocol]] for sharing resources using packet-switching among the nodes.<ref>{{Cite journal|last1=Cerf|first1=V.|last2=Kahn|first2=R.|date=1974|title=A Protocol for Packet Network Intercommunication|url=https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://www.cs.princeton.edu/courses/archive/fall06/cos561/papers/cerf74.pdf |archive-date=2022-10-10 |url-status=live|journal=IEEE Transactions on Communications|volume=22|issue=5|pages=637–648|doi=10.1109/TCOM.1974.1092259|issn=1558-0857|quote=The authors wish to thank a number of colleagues for helpful comments during early discussions of international network protocols, especially R. Metcalfe, R. Scantlebury, D. Walden, and H. Zimmerman; D. Davies and L. Pouzin who constructively commented on the fragmentation and accounting issues; and S. Crocker who commented on the creation and destruction of associations.}}</ref> The specifications of the TCP were then published in {{IETF RFC|675}} (''Specification of Internet Transmission Control Program''), written by Vint Cerf, [[Yogen Dalal]] and Carl Sunshine in December 1974.<ref>{{cite IETF |title=Specification of Internet Transmission Control Protocol |rfc=675 |last1=Cerf |first1=Vinton |last2=Dalal |first2=Yogen |last3=Sunshine |first3=Carl |date=December 1974 |publisher=[[IETF]]}}</ref> 

The [[X.25|X.25 protocol]], developed by [[Rémi Després]] and others, was built on the concept of [[virtual circuit]]s. In the mid-late 1970s and early 1980s, national and international [[public data network]]s emerged using X.25 which was developed with participation from France, the UK, Japan, USA and Canada. It was complemented with [[X.75]] to enable internetworking.<ref name=":27">{{Cite web |last=Postel |first=Jon |date=August 29, 1979 |title=Comparison of X.25 and TCP Version 4 as Cable-bus Network Protocols |url=https://www.rfc-editor.org/ien/ien130.pdf}}</ref> 

Packet switching was shown to be optimal in the [[Huffman coding]] sense in 1978.<ref>{{Cite journal |last1=Camrass |first1=R. |last2=Gallager |first2=R. |date=1978 |title=Encoding message lengths for data transmission (Corresp.) |journal=IEEE Transactions on Information Theory |language=en |volume=24 |issue=4 |pages=495–496 |doi=10.1109/TIT.1978.1055910 |issn=0018-9448}}</ref><ref>{{Cite web |title=Reflections on an Internet pioneer: Roger Camrass |url=http://stories.clare.cam.ac.uk/reflections-of-an-internet-pioneer/ |access-date=2024-07-01 |website=stories.clare.cam.ac.uk |language=en}}</ref>  

In the late 1970s, the monolithic Transmission Control Program was layered as the Transmission Control Protocol (TCP), atop the [[Internet Protocol]] (IP). Many [[Internet pioneers]] developed this into the [[Internet protocol suite]] and the associated Internet architecture and governance that emerged in the 1980s.<ref>{{Cite web |last1=Cerf |first1=Vinton G. |last2=Postel |first2=Jon |date=August 18, 1977 |title=Specification of Internetwork Transmission Program: TCP Version 3 |url=https://www.rfc-editor.org/ien/ien21.pdf |page=iii, 75-87}}</ref><ref>{{Cite web |last=Postel |first=Jon |date=September 1978 |title=Specification of Internetwork Transmission Control Protocol: TCP Version 4 |url=https://www.rfc-editor.org/ien/ien55.pdf |pages=iii, 85-97}}</ref><ref>{{Cite web |last=Cerf |first=Vinton G. |date=1 April 1980 |title=Final Report of the Stanford University TCP Project |url=https://www.rfc-editor.org/ien/ien151.txt}}</ref><ref name="Moschovitisp118">{{harvnb|Moschovitis|1999|p=[https://archive.org/details/historyofinterne0000unse/page/118/mode/2up 78-9]}}</ref><ref name="ISINames-2003">[https://www3.isi.edu/news/story/54 "ISI Names Dr. Paul Mockapetris Visiting Scholar"] {{webarchive|url=https://web.archive.org/web/20120826032920/http://www3.isi.edu/about-news_story.htm?s=54|date=2012-08-26}}, Information Sciences Institute, University of Southern California, 27 March 2003</ref><ref>[http://portal.acm.org/citation.cfm?doid=205447.205462 "Congestion avoidance and control"], Van Jacobson, ACM SIGCOMM Computer Communication Review - Special twenty-fifth anniversary issue, Highlights from 25 years of the Computer Communication Review, Volume 25 Issue 1, Jan. 1995, pp.157-187</ref>

For a period in the 1980s and early 1990s, the network engineering community was polarized over the implementation of competing protocol suites, commonly known as the [[Protocol Wars]]. It was unclear which of the Internet protocol suite and the [[OSI model]] would result in the best and most robust computer networks.<ref name="ieee201703">{{cite magazine |author=Andrew L. Russell |date=30 July 2013 |title=OSI: The Internet That Wasn't |url=https://spectrum.ieee.org/osi-the-internet-that-wasnt |magazine=[[IEEE Spectrum]] |volume=50 |issue=8}}</ref><ref>{{Cite web |last=Russell |first=Andrew L. |title=Rough Consensus and Running Code' and the Internet-OSI Standards War |url=https://www2.cs.duke.edu/courses/common/compsci092/papers/govern/consensus.pdf |url-status=live |archive-url=https://web.archive.org/web/20191117080112/https://www2.cs.duke.edu/courses/common/compsci092/papers/govern/consensus.pdf |archive-date=2019-11-17 |publisher=IEEE Annals of the History of Computing}}</ref><ref>{{Cite book |last1=Davies |first1=Howard |chapter-url=https://books.google.com/books?id=DN-t8MpZ0-wC&q=%22protocol+wars%22&pg=PA106 |title=A History of International Research Networking: The People who Made it Happen |last2=Bressan |first2=Beatrice |date=2010 |publisher=John Wiley & Sons |isbn=978-3-527-32710-2 |pages=106–110 |language=en |chapter=The Protocol Wars}}</ref>

Leonard Kleinrock carried out theoretical work at UCLA during the 1970s analyzing throughput and delay in the ARPANET.<ref>{{Cite web |last=Postel |first=J. |date=7 February 1979 |title=Internet Meeting Notes -- 25 & 26 January 1979 |url=https://www.rfc-editor.org/ien/ien76.pdf |access-date=9 February 2022 |page=5 |quote=Vint noted that UCLA's internet work is primarily theoretical research on throughput and delay analysis. This work is headed by L. Kleinrock.}}</ref><ref>{{cite tech report |url=https://walden-family.com/bbn/arpanet-completion-report.pdf |title=Arpanet Completion Report |last1=Heart |first1=F. |last2=McKenzie |first2=A. |last3=McQuillian |first3=J. |last4=Walden |first4=D. |date=January 4, 1978 |archive-url=https://web.archive.org/web/20230527095942/https://walden-family.com/bbn/arpanet-completion-report.pdf |url-status=dead |archive-date=2023-05-27 |publisher=Bolt, Beranek and Newman |location=Burlington, MA}}</ref><ref name=":43">{{Cite book |last=Davies |first=Donald Watts |url=https://archive.org/details/computernetworks00davi/page/86/mode/2up?q=kleinrock+kleinrock%27s |title=Computer networks and their protocols |date=1979 |publisher=Wiley |others=Internet Archive |isbn=978-0-471-99750-4 |pages=See page refs highlighted at url |quote=In mathematical modelling use is made of the theories of queueing processes and of flows in networks, describing the performance of the network in a set of equations. ... The analytic method has been used with success by Kleinrock and others, but only if important simplifying assumptions are made. ... It is heartening in Kleinrock's work to see the good correspondence achieved between the results of analytic methods and those of simulation.}}</ref> His theoretical work on [[hierarchical routing]] with student [[Farouk Kamoun]] became critical to the operation of the Internet.<ref name=":52">{{Cite book |last=Davies |first=Donald Watts |url=https://archive.org/details/computernetworks00davi/page/110/mode/2up?q=%22kleinrock+and+kamoun%22 |title=Computer networks and their protocols |date=1979 |publisher=Wiley |others=Internet Archive |isbn=978-0-471-99750-4 |pages=110–111 |quote=Hierarchical addressing systems for network routing have been proposed by Fultz and, in greater detail, by McQuillan. A recent very full analysis may be found in Kleinrock and Kamoun.}}</ref><ref>{{Cite book |last1=Feldmann |first1=Anja |title=Proceedings of the 2009 workshop on Re-architecting the internet |last2=Cittadini |first2=Luca |last3=Mühlbauer |first3=Wolfgang |last4=Bush |first4=Randy |last5=Maennel |first5=Olaf |date=2009 |publisher=Association for Computing Machinery |isbn=978-1-60558-749-3 |series=ReArch '09 |location=New York, NY, USA |pages=43–48 |chapter=HAIR: Hierarchical architecture for internet routing |doi=10.1145/1658978.1658990 |quote=The hierarchical approach is further motivated by theoretical results (e.g., [16]) which show that, by optimally placing separators, i.e., elements that connect levels in the hierarchy, tremendous gain can be achieved in terms of both routing table size and update message churn. ... [16] KLEINROCK, L., AND KAMOUN, F. Hierarchical routing for large networks: Performance evaluation and optimization. Computer Networks (1977). |chapter-url=https://core.ac.uk/download/pdf/326320693.pdf |s2cid=2930578}}</ref> Kleinrock published hundreds of research papers,<ref name=":26">{{Cite web |title=Leonard Kleinrock |url=https://www.internethalloffame.org/inductee/leonard-kleinrock/ |access-date=2023-03-13 |website=Internet Hall of Fame |language=en-US}}</ref><ref name=":32">{{Cite web |title=Kleinrock (Leonard) papers |url=https://oac.cdlib.org/findaid/ark:/13030/c8kd240b/entire_text/ |access-date=2023-04-04 |website=oac.cdlib.org}}</ref> which ultimately launched a new field of research on the theory and application of queuing theory to computer networks.<ref name=":12" /><ref name="Abbatep81">{{Cite book |last=Abbate |first=Janet |url=https://archive.org/details/inventinginterne00jane/page/80/mode/2up |title=Inventing the Internet |date=1999 |publisher=MIT Press |others=Internet Archive |isbn=978-0-262-01172-3 |page=81}}</ref>

Complementary [[metal–oxide–semiconductor]] ([[CMOS]]) [[VLSI]] (very-[[large-scale integration]]) technology led to the development of high-speed [[broadband]] packet switching during the 1980s{{ndash}}1990s.<ref name="Hayward">{{cite journal |last1=Hayward |first1=G. |last2=Gottlieb |first2=A. |last3=Jain |first3=S. |last4=Mahoney |first4=D. |title=CMOS VLSI Applications in Broadband Circuit Switching |journal=IEEE Journal on Selected Areas in Communications |date=October 1987 |volume=5 |issue=8 |pages=1231–1241 |doi=10.1109/JSAC.1987.1146652 |issn=1558-0008}}</ref><ref name="Hui">{{cite journal |last1=Hui |first1=J. |last2=Arthurs |first2=E. |title=A Broadband Packet Switch for Integrated Transport |journal=IEEE Journal on Selected Areas in Communications |date=October 1987 |volume=5 |issue=8 |pages=1264–1273 |doi=10.1109/JSAC.1987.1146650 |issn=1558-0008}}</ref><ref>{{cite book |last1=Gibson |first1=Jerry D. |title=The Communications Handbook |date=2018 |publisher=[[CRC Press]] |isbn=9781420041163|url=https://books.google.com/books?id=Tokk5bZxB0MC&pg=SA34-PA4}}</ref>

=== The "paternity dispute" ===

Roberts claimed in later years that, by the time of the October 1967 SOSP, he already had the concept of packet switching in mind (although not yet named and not written down in his paper published at the conference, which a number of sources describe as "vague"), and that this originated with his old colleague, Kleinrock, who had written about such concepts in his Ph.D. research in 1961-2.<ref name=":19" /><ref name=":18" /><ref name=":20" /><ref>{{Cite journal |last=Kirstein |first=Peter T. |date=2009 |title=The early history of packet switching in the UK |journal=IEEE Communications Magazine |volume=47 |issue=2 |pages=18–26 |doi=10.1109/MCOM.2009.4785372 |s2cid=34735326 |quote=It is more difficult to establish at this time, however, whether Larry intended to switch the fragments as independent packets in the ARPAnet before he heard of the NPL work; certainly he now claims that this was always his intention.}}</ref><ref>{{Cite web |last=technicshistory |date=2019-06-02 |title=ARPANET, Part 2: The Packet |url=https://technicshistory.com/2019/06/02/arpanet-part-2-the-packet/ |access-date=2024-06-21 |website=Creatures of Thought |language=en |quote=The above description of how packet-switching came to be is the most widely-accepted one. However, there is an alternative version. Roberts claimed in later years that by the time of the Gatlinburg symposium, he already had the basic concepts of packet-switching well in mind, and that they originated with his old colleague Len Kleinrock, who had written about them as early as 1962, as part of his Ph.D. research on communication nets. It requires a great deal of squinting to extract anything resembling packet-switching from Kleinrock’s work, however, and no other contemporary textual evidence that I have come across backs the Kleinrock/Roberts account.}}</ref> In 1997, along with seven other [[Internet pioneers]], Roberts and Kleinrock co-wrote "Brief History of the Internet" published by the [[Internet Society]].<ref>{{citation |author= Barry M. Leiner, Vinton G. Cerf, David D. Clark, Robert E. Kahn, Leonard Kleinrock, Daniel C. Lynch, Jon Postel, Larry G. Roberts, Stephen Wolff |title=Brief History of the Internet |publisher=Internet Society |date=1997|url=https://www.internetsociety.org/resources/doc/2017/brief-history-internet/}}</ref> In it, Kleinrock is described as having "published the first paper on packet switching theory in July 1961 and the first book on the subject in 1964". Many sources about the history of the Internet began to reflect these claims as uncontroversial facts. This became the subject of what [[Katie Hafner]] called a "paternity dispute" in The New York Times in 2001.<ref name=":8">{{citation |author=Katie Hafner |title=A Paternity Dispute Divides Net Pioneers |date=November 8, 2001 |url=https://www.nytimes.com/2001/11/08/technology/a-paternity-dispute-divides-net-pioneers.html?pagewanted=all |newspaper=New York Times |quote="The Internet is really the work of a thousand people," Mr. Baran said. "And of all the stories about what different people have done, all the pieces fit together. It's just this one little case that seems to be an aberration."}}</ref>

The disagreement about Kleinrock's contribution to packet switching dates back to a version of the above claim made on Kleinrock's profile on the UCLA Computer Science department website sometime in the 1990s. Here, he was referred to as the "Inventor of the Internet Technology".<ref>{{cite web |last1=UCLA Computer Science Dept. |title=Leonard Kleinrock, Professor (archived) |url=http://www.lk.cs.ucla.edu |website=UCLA Computer Science Dept. |access-date=28 December 2023 |archive-url=https://web.archive.org/web/20040227150208/http://www.lk.cs.ucla.edu:80/index.html |archive-date=Feb 27, 2004}}</ref> The webpage's depictions of Kleinrock's achievements provoked anger among some early Internet pioneers.<ref name=":0">{{cite book |last1=Isaacson |first1=Walter |url=https://books.google.com/books?id=4V9koAEACAAJ&pg=PA245 |title=The Innovators: How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution |date=2014 |publisher=Simon & Schuster |isbn=9781476708690 |pages=244–6 |author-link=Walter Isaacson}}</ref> The dispute over [[Scientific priority|priority]] became a public issue after Donald Davies posthumously published a paper in 2001 in which he denied that Kleinrock's work was related to packet switching. Davies also described ARPANET project manager [[Lawrence Roberts (scientist)|Larry Roberts]] as supporting Kleinrock, referring to Roberts' writings online and Kleinrock's UCLA webpage profile as "very misleading".<ref>{{citation |author=Donald W. Davies |title=An Historical Study of the Beginnings of Packet Switching |date=2001 |url=https://academic.oup.com/comjnl/article-abstract/44/3/152/415514 |journal=The Computer Journal |volume=44 |issue=3 |pages=152–162 |doi=10.1093/comjnl/44.3.152 |quote=I can find no evidence that he understood the principles of packet switching.}}</ref><ref name=":9">{{Cite journal |last=Harris |first=Trevor, University of Wales |date=2009 |editor-last=Pasadeos |editor-first=Yorgo |title=Who is the Father of the Internet? The Case for Donald Davies |url=https://www.academia.edu/378261 |url-status=dead |journal=Variety in Mass Communication Research |language=en |publisher=ATINER |pages=123–134 |isbn=978-960-6672-46-0 |archive-url=https://web.archive.org/web/20220502025941/https://www.academia.edu/378261/Who_is_the_Father_of_the_Internet_The_Case_for_Donald_Davies |archive-date=May 2, 2022 |quote=Leonard Kleinrock and Lawrence (Larry) Roberts, neither of whom were directly involved in the invention of packet switching ... Dr Willis H. Ware, Senior Computer Scientist and Research at the RAND Corporation, notes that Davies (and others) were troubled by what they regarded as in appropriate claims on the invention of packet switching}}</ref> [[Walter Isaacson]] wrote that Kleinrock's claims "led to an outcry among many of the other Internet pioneers, who publicly attacked Kleinrock and said that his brief mention of breaking messages into smaller pieces did not come close to being a proposal for packet switching".<ref name=":0" /> 

Davies' paper reignited a previous dispute over who deserves credit for getting the ARPANET online between engineers at [[Bolt, Beranek, and Newman]] (BBN) who had been involved in building and designing the ARPANET IMP on the one side, and ARPA-related researchers on the other.<ref name=":2A3" /><ref name="F.E. Froehlich, A. Kent" /> This earlier dispute is exemplified by BBN's [[Will Crowther]], who in a 1990 oral history described Paul Baran's packet switching design (which he called [[hot-potato routing]]), as "crazy" and non-sensical, despite the ARPA team having advocated for it.<ref>{{citation|author=Judy O'Neill | title=Oral history interview with William Crowther| date=12 March 1990| hdl=11299/107235|url=https://conservancy.umn.edu/handle/11299/107235|quote=...there were all sorts of crazy ideas about, and most of them didn't make any sense. There was this 'hot potato' routing which somebody was advocating, which was just crazy.}}</ref> The reignited debate caused other former BBN employees to make their concerns known, including Alex McKenzie, who followed Davies in disputing that Kleinrock's work was related to packet switching, stating "... there is nothing in the entire 1964 book that suggests, analyzes, or alludes to the idea of packetization".<ref>{{citation |author=Alex McKenzie |title=Comments on Dr. Leonard Kleinrock's claim to be "the Father of Modern Data Networking" |year=2009 |url=http://alexmckenzie.weebly.com/comments-on-kleinrocks-claims.html |access-date=April 23, 2015}}</ref>

Former [[Information Processing Techniques Office|IPTO]] director [[Robert W. Taylor|Bob Taylor]] also joined the debate, stating that "authors who have interviewed dozens of Arpanet pioneers know very well that the Kleinrock-Roberts claims are not believed".<ref>{{citation|author=Robert Taylor|title=Birthing the Internet: Letters From the Delivery Room; Disputing a Claim|date=November 22, 2001|url=https://www.nytimes.com/2001/11/22/technology/l-birthing-the-internet-letters-from-the-delivery-room-disputing-a-claim-325210.html|newspaper=New York Times|author-link=Robert Taylor (computer scientist)}}</ref> Walter Isaacson notes that "until the mid-1990s Kleinrock had credited [Baran and Davies] with coming up with the idea of packet switching".<ref name=":0" />

A subsequent version of Kleinrock's biography webpage was copyrighted in 2009 by Kleinrock.<ref>{{citation |author=Leonard Kleinrock |title=Leonard Kleinrock - UCLA Dept. of Computer Science |url=https://www.lk.cs.ucla.edu/index.html |archive-url=https://web.archive.org/web/20231205193349/https://www.lk.cs.ucla.edu/index.html |archive-date=December 5, 2023 |quote=He developed the mathematical theory of data networks, the technology underpinning the Internet, while a graduate student at MIT in the period from 1960-1962.  In that work, he also modeled the packetization of messages and solved for a key performance gain that packetization provides.}}</ref> He was called on to defend his position over subsequent decades.<ref name=":14">{{citation |last1=Schwartz |first1=Mischa |last2=Adamson |first2=Greg |last3=Kleinrock |first3=Leonard |title=Letters to the editor |journal=IEEE Communications |date=February 2011|volume=49 |issue=2 |page=12 |doi=10.1109/MCOM.2011.5706298 |bibcode=2011IComM..49b..12S }}</ref> In 2023, he acknowledged that his published work in the early 1960s was about message switching and claimed he was thinking about packet switching.<ref>{{Cite AV media |url=https://www.inc.com/computerfreaks |title=Computer Freaks |date=June 22, 2023 |last=Haughney Dare-Bryan |first=Christine |type=Podcast |publisher=Inc. Magazine |series=Chapter Two: In the Air}}</ref> Primary sources and historians recognize Baran and Davies for independently inventing the concept of digital packet switching used in modern computer networking including the ARPANET and the Internet.<ref name=":16" /><ref name="Pelkeyp42" /><ref name="Abbate2000-2" /><ref name=":13">{{Cite book |last1=Norberg |first1=Arthur L. |title=Transforming computer technology: information processing for the Pentagon, 1962-1986 |last2=O'Neill |first2=Judy E. |date=1996 |publisher=Johns Hopkins Univ. Press |isbn=978-0-8018-5152-0 |series=Johns Hopkins studies in the history of technology New series |location=Baltimore |pages=153–196}} Prominently cites Baran and Davies as sources of inspiration, and nowhere mentions Kleinrock's work.</ref><ref>{{cite report |url=https://apps.dtic.mil/sti/pdfs/ADA115440.pdf |title=A History of the ARPANET: The First Decade |date=1 April 1981 |publisher=Bolt, Beranek & Newman Inc. |pages=13, 53 of 183 |quote=Aside from the technical problems of interconnecting computers with communications circuits, the notion of computer networks had been considered in a number of places from a theoretical point of view. Of particular note was work done by Paul Baran and others at the Rand Corporation in a study "On Distributed Communications" in the early 1960's. Also of note was work done by Donald Davies and others at the National Physical Laboratory in England in the mid-1960's. ... Another early major network development which affected development of the ARPANET was undertaken at the National Physical Laboratory in Middlesex, England, under the leadership of D. W. Davies. |archive-url=https://web.archive.org/web/20121201013642/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA115440 |archive-date=1 December 2012 |url-status=live}}</ref>

Kleinrock has received many awards for his ground-breaking [[applied mathematical research]] on packet switching, carried out in the 1970s, which was an extension of his pioneering work in the early 1960s on the optimization of message delays in communication networks.<ref name=":12" /><ref>{{Cite web |title=Leonard Kleinrock |url=https://samueli.ucla.edu/people/leonard-kleinrock/ |access-date=2024-01-20 |website=UCLA Samueli School Of Engineering |language=en-US}}</ref> However, Kleinrock's claims that his work in the early 1960s originated the concept of packet switching and that his work was a source of the packet switching concepts used in the ARPANET have affected sources on the topic, which has created methodological challenges in the historiography of the Internet.<ref name=":8" /><ref name=":0" /><ref name=":9" /><ref name=":14" /> Historian Andrew L. Russell said "'Internet history' also suffers from a ... methodological, problem: it tends to be too close to its sources. Many Internet pioneers are alive, active, and eager to shape the histories that describe their accomplishments. Many museums and historians are equally eager to interview the pioneers and to publicize their stories".<ref>{{Cite conference |last=Russell |first=Andrew |date=2012 |title=Histories of Networking vs. the History of the Internet |url=https://arussell.org/papers/russell-SIGCIS-2012.pdf |conference=2012 SIGCIS Workshop |page=6}}</ref>

==Connectionless and connection-oriented modes==
Packet switching may be classified into [[connectionless]] packet switching, also known as [[datagram]] switching, and [[connection-oriented]] packet switching, also known as [[virtual circuit]] switching. Examples of connectionless systems are Ethernet, IP, and the [[User Datagram Protocol]] (UDP). Connection-oriented systems include X.25, [[Frame Relay]], [[Multiprotocol Label Switching]] (MPLS), and TCP.

In connectionless mode each packet is labeled with a destination address, source address, and port numbers. It may also be labeled with the sequence number of the packet. This information eliminates the need for a pre-established path to help the packet find its way to its destination, but means that more information is needed in the packet header, which is therefore larger. The packets are routed individually, sometimes taking different paths resulting in [[out-of-order delivery]]. At the destination, the original message may be reassembled in the correct order, based on the packet sequence numbers. Thus a [[virtual circuit]] carrying a [[byte stream]] is provided to the application by a [[transport layer]] protocol, although the network only provides a connectionless [[network layer]] service.

Connection-oriented transmission requires a setup phase to establish the parameters of communication before any packet is transferred. The [[signaling (telecommunications)|signaling]] protocols used for setup allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated. The packets transferred may include a connection identifier rather than address information and the packet header can be smaller, as it only needs to contain this code and any information, such as length, timestamp, or sequence number, which is different for different packets. In this case, address information is only transferred to each node during the connection setup phase, when the route to the destination is discovered and an entry is added to the switching table in each network node through which the connection passes. When a connection identifier is used, routing a packet requires the node to look up the connection identifier in a table.{{citation needed|date=April 2021}}

Connection-oriented transport layer protocols such as TCP provide a connection-oriented service by using an underlying connectionless network. In this case, the end-to-end principle dictates that the end nodes, not the network itself, are responsible for the connection-oriented behavior.

==Packet switching in networks==
In telecommunication networks, packet switching is used to optimize the usage of [[channel capacity]] and increase [[Robustness (computer science)|robustness]].<ref name=":20" /> Compared to [[circuit switching]], packet switching is highly dynamic, allocating channel capacity based on usage instead of explicit reservations. This can reduce wasted capacity caused by underutilized reservations at the cost of removing bandwidth guarantees. In practice, [[TCP congestion control|congestion control]] is generally used in IP networks to dynamically negotiate capacity between connections. Packet switching may also increase the robustness of networks in the face of failures. If a node fails, connections do not need to be interrupted, as packets may be routed around the failure.

Packet switching is used in the [[Internet]] and most [[local area network]]s. The Internet is implemented by the [[Internet Protocol Suite]] using a variety of [[link layer]] technologies. For example, Ethernet and Frame Relay are common. Newer [[mobile phone]] technologies (e.g., [[GSM]], [[LTE (telecommunication)|LTE]]) also use packet switching. Packet switching is associated with connectionless networking because, in these systems, no connection agreement needs to be established between communicating parties prior to exchanging data.

[[X.25]], the international [[CCITT]] standard of 1976, is a notable use of packet switching in that it provides to users a service of [[flow control (data)|flow-controlled]] [[virtual circuit]]s. These virtual circuits reliably carry variable-length packets with data order preservation. [[DATAPAC]] in Canada was the first public network to support X.25, followed by [[Transpac (data network)|TRANSPAC]] in France.<ref name="Transpac paper"/>

[[Asynchronous Transfer Mode]] (ATM) is another virtual circuit technology. It differs from X.25 in that it uses small fixed-length packets ([[cell relay|cells]]), and that the network imposes no [[flow control (data)|flow control]] to users.

Technologies such as MPLS and the [[Resource Reservation Protocol]] (RSVP) create virtual circuits on top of datagram networks. MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells".<ref>{{cite web|url=http://www.certificationzone.com/cisco/newsletter/SL/interview_08-12-03.html|title=Interview with the author (of an MPLS-based VPN article)|archive-url=https://web.archive.org/web/20070929150800/http://www.certificationzone.com/cisco/newsletter/SL/interview_08-12-03.html|archive-date=2007-09-29|first=G.|last=Pildush}}</ref> Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications.

==Packet-switched networks==
{{Further|History of the Internet}}
Donald Davies' work in the late 1960s on data communications and computer network design became well known in the United States, Europe and Japan.<ref name="frs" /><ref name=":110">{{Cite news |last=Feder |first=Barnaby J. |date=2000-06-04 |title=Donald W. Davies, 75, Dies; Helped Refine Data Networks |url=https://www.nytimes.com/2000/06/04/business/donald-w-davies-75-dies-helped-refine-data-networks.html |access-date=2020-01-10 |work=The New York Times |language=en-US |issn=0362-4331 |quote=Donald W. Davies, who proposed a method for transmitting data that made the Internet possible}}</ref><ref>{{Citation |last=Berners-Lee |first=Tim |title=Weaving the Web: The Past, Present and Future of the World Wide Web by its Inventor |page=[https://archive.org/details/weavingweb00timb/page/7 7] |year=1999 |url=https://archive.org/details/weavingweb00timb/page/7 |place=London |publisher=Orion |isbn=0-75282-090-7 |author-link=Tim Berners-Lee}} "The advances by Donald Davies, by Paul Baran, and by Vint Cerf, Bob Khan and colleagues had already happened in the 1970s but were only just becoming pervasive."</ref><ref>{{Cite news |date=2013-07-25 |title=Treorchy internet pioneer Donald Davies honoured |url=https://www.bbc.com/news/uk-wales-23446159 |access-date=2024-07-01 |work=BBC News |language=en-GB |quote=[Davies] is widely known in America which continued his computer work}}</ref> It was the "cornerstone" that inspired numerous packet switching networks in the decade following.<ref>{{Cite book |last=Yates |first=David M. |url=https://books.google.com/books?id=ToMfAQAAIAAJ&q=%22led+to+the+Internet%22 |title=Turing's Legacy: A History of Computing at the National Physical Laboratory 1945-1995 |date=1997 |publisher=National Museum of Science and Industry |isbn=978-0-901805-94-2 |pages=132–34 |language=en |quote=Davies's invention of packet switching and design of computer communication networks ... were a cornerstone of the development which led to the Internet}}</ref><ref>{{Cite journal |last=Harris |first=Trevor, University of Wales |date=2009 |editor-last=Pasadeos |editor-first=Yorgo |title=Who is the Father of the Internet? The Case for Donald Davies |url=https://www.academia.edu/378261 |url-status=dead |journal=Variety in Mass Communication Research |language=en |publisher=ATINER |pages=123–134 |isbn=978-960-6672-46-0 |archive-url=https://web.archive.org/web/20220502025941/https://www.academia.edu/378261/Who_is_the_Father_of_the_Internet_The_Case_for_Donald_Davies |archive-date=May 2, 2022}}</ref><ref>{{Cite web |last=Archives |first=L. A. Times |date=2000-06-03 |title=Donald W. Davies; Work Led to the Internet |url=https://www.latimes.com/archives/la-xpm-2000-jun-03-me-36923-story.html |access-date=2024-01-21 |website=Los Angeles Times |language=en-US}}</ref><ref name=":24" /> 

The history of packet-switched networks can be divided into three overlapping eras: early networks before the introduction of X.25; the X.25 era when many [[postal, telegraph and telephone service|postal, telephone, and telegraph]] (PTT) companies provided [[public data network]]s with X.25 interfaces; and the [[Internet]] era which initially [[Protocol Wars|competed with]] the [[OSI model]].<ref>{{cite web|last1=Moore|first1=Roger D.|title=This is a temporary index for a collection of papers about packet-switching in the 1970s|url=http://rogerdmoore.ca/PS/|access-date=5 September 2017|date=August 2006|archive-date=24 July 2017|archive-url=https://web.archive.org/web/20170724223235/http://rogerdmoore.ca/PS/|url-status=dead}}</ref><ref>{{cite web|last1=Kirstein|first1=Peter T.|title=A SURVEY OF PRESENT AMD PLANNED GENERAL PURPOSE EUROPEAN DATA AND COMPUTER NETWORKS|url=http://rogerdmoore.ca/PS/Kirs1973/Ki.html|access-date=5 September 2017|date=1973|archive-date=2 March 2017|archive-url=https://web.archive.org/web/20170302092943/http://rogerdmoore.ca/PS/Kirs1973/Ki.html|url-status=dead}}</ref><ref>{{cite book|author1=National Research Council (U.S.). National Research Network Review Committee, Leonard Kleinrock|url=https://books.google.com/books?id=gGYrAAAAYAAJ&pg=PA40|title=Toward a National Research Network|date=1988|publisher=National Academies|page=40|isbn = 9780309581257|display-authors=etal}}</ref>

===Early networks===
Research into packet switching at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL) began with a proposal for a wide-area network in 1965,<ref name="Roberts1978">{{cite web |last1=Roberts |first1=Dr. Lawrence G. |date=November 1978 |title=The Evolution of Packet Switching |url=http://www.packet.cc/files/ev-packet-sw.html |url-status=dead |archive-url=https://web.archive.org/web/20160324033133/http://www.packet.cc/files/ev-packet-sw.html |archive-date=24 March 2016 |access-date=5 September 2017}}</ref> and a local-area network in 1966.<ref>{{cite web|title=A SURVEY OF THE CAPABILITIES OF 8 PACKET SWITCHING NETWORKS|url=http://rogerdmoore.ca/PS/Wood.html|date=1975|access-date=5 September 2017|quote=Research in packet switching networks at the British National Physical Laboratory (NPL) predates ARPANET, having commenced in 1966.|archive-date=26 April 2017|archive-url=https://web.archive.org/web/20170426104253/http://rogerdmoore.ca/PS/Wood.html|url-status=dead}}</ref> ARPANET funding was secured in 1966 by [[Robert Taylor (computer scientist)|Bob Taylor]], and planning began in 1967 when he hired [[Lawrence Roberts (scientist)|Larry Roberts]]. The NPL network followed by the ARPANET became operational in 1969, the first two networks to use packet switching.<ref name=":22"/><ref name="Haughney Dare-Bryan">{{Cite AV media |url=https://www.inc.com/computerfreaks |title=Computer Freaks |date=June 22, 2023 |last=Haughney Dare-Bryan |first=Christine |type=Podcast |publisher=Inc. Magazine |series=Chapter Two: In the Air |minutes=35:55 |quote=Leonard Kleinrock: Donald Davies ... did make a single node packet switch before ARPA did}}</ref> Larry Roberts said many of the packet switching networks built in the 1970s were similar "in nearly all respects" to Donald Davies' original 1965 design.<ref name=":24">{{cite journal |last1=Roberts |first1=Lawrence G. |date=November 1978 |title=The Evolution of Packet Switching |url=http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf |url-status=dead |journal=IEEE Invited Paper |archive-url=https://web.archive.org/web/20181231092936/http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf |archive-date=31 December 2018 |access-date=September 10, 2017 |quote=In nearly all respects, Davies' original proposal, developed in late 1965, was similar to the actual networks being built today.}}</ref>  The ARPANET and Louis Pouzin's CYCLADES were the primary precursor networks of the modern [[Internet]].<ref name="Bennett20092" /> CYCLADES, unlike ARPANET, was explicitly designed to research internetworking.<ref name=":28" />

Before the introduction of X.25 in 1976,<ref>{{cite web
|url= http://www.networkworld.com/newsletters/frame/2008/0128wan1.html
|title= Vint Cerf on why TCP/IP was so long in coming
|first= Steve
|last= Taylor
|author2= Jim Metzler
|year= 2008
|access-date= 2013-08-30
|archive-date= 2013-06-21
|archive-url= https://web.archive.org/web/20130621100237/http://www.networkworld.com/newsletters/frame/2008/0128wan1.html
|url-status= dead
}}</ref> about twenty different network technologies had been developed. Two fundamental differences involved the division of functions and tasks between the hosts at the edge of the network and the network core. In the datagram system, operating according to the end-to-end principle, the hosts have the responsibility to ensure orderly delivery of packets. In the [[virtual call capability|virtual call]] system, the network guarantees sequenced delivery of data to the host. This results in a simpler host interface but complicates the network. The X.25 protocol suite uses this network type.

===={{anchor|Appletalk}}AppleTalk====
[[AppleTalk]] is a proprietary suite of networking protocols developed by [[Apple Inc.|Apple]] in 1985 for [[Apple Macintosh]] computers. It was the primary protocol used by Apple devices through the 1980s and 1990s. AppleTalk included features that allowed [[local area network]]s to be established ''ad hoc'' without the requirement for a centralized router or server. The AppleTalk system automatically assigned addresses, updated the distributed namespace, and configured any required [[Internetworking|inter-network routing]]. It was a [[plug-n-play]] system.<ref name=Oppenheimer>{{cite web|url=http://www.opendoor.com/nethistory/MacWorld2004/index.html|title=A History of Macintosh Networking|archive-url=https://web.archive.org/web/20061016132614/http://www.opendoor.com/nethistory/MacWorld2004/index.html|archive-date=2006-10-16|first=Alan|last=Oppenheimer|website=MacWorld Expo|date=January 2004}}</ref><ref>{{cite book|title=Inside AppleTalk|edition=2|first1=Gursharan|last1=Sidhu|first2=Richard|last2=Andrews|first3=Alan|last3=Oppenheiner|publisher=Addison-Wesley|year=1989|isbn=0-201-55021-0}}</ref>

AppleTalk implementations were also released for the [[IBM PC]] and compatibles, and the [[Apple IIGS]]. AppleTalk support was available in most networked printers, especially [[laser printer]]s, some [[file server]]s and [[router (computing)|router]]s.

The protocol was designed to be simple, autoconfiguring, and not require servers or other specialized services to work. These benefits also created drawbacks, as Appletalk tended not to use bandwidth efficiently. AppleTalk support was terminated in 2009.<ref name="Oppenheimer" /><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>

====ARPANET====
The [[ARPANET]] was a progenitor network of the Internet and one of the first networks, along with ARPA's [[SATNET]], to run the [[TCP/IP]] suite using packet switching technologies.

====BNRNET====
BNRNET was a network which [[Bell-Northern Research]] developed for internal use. It initially had only one host but was designed to support many hosts. BNR later made major contributions to the CCITT X.25 project.<ref>{{cite conference
|first= C. C.
|last= Martel
|author2= J. M. Cunningham
|author3= M. S. Grushcow
|title= THE BNR NETWORK: A CANADIAN EXPERIENCE WITH PACKET SWITCHING TECHNOLOGY
|book-title= IFIP Congress 1974
|pages= 10–14
|url= http://rogerdmoore.ca/PS/BNR/BNRnet.html
|conference= 
|access-date= 2013-08-30
|archive-date= 2013-10-20
|archive-url= https://web.archive.org/web/20131020142453/http://rogerdmoore.ca/PS/BNR/BNRnet.html
|url-status= dead
}}</ref>

====Cambridge Ring====

The [[Cambridge Ring (computer network)|Cambridge Ring]] was an experimental [[ring network]] developed at the [[Computer Laboratory, University of Cambridge]]. It operated from 1974 until the 1980s.

==== CompuServe ====
[[CompuServe]] developed its own packet switching network, implemented on DEC [[PDP-11]] minicomputers acting as network nodes that were installed throughout the US (and later, in other countries) and interconnected. Over time, the CompuServe network evolved into a complicated multi-tiered network incorporating ATM, Frame Relay, IP and X.25 technologies.

====CYCLADES====
The [[CYCLADES]] packet switching network was a French research network designed and directed by [[Louis Pouzin]]. First demonstrated in 1973, it was developed to explore alternatives to the early ARPANET design and to support network research generally. It was the first network to use the end-to-end principle and make the hosts responsible for reliable delivery of data, rather than the network itself. Concepts of this network influenced later ARPANET architecture.<ref>{{cite web|url=http://www.cs.utexas.edu/users/chris/think/Cyclades/index.shtml|title=A Technical History of CYCLADES|work=Technical Histories of the Internet & other Network Protocols|publisher=Computer Science Department, University of Texas Austin|url-status=dead|archive-url=https://web.archive.org/web/20130901092641/http://www.cs.utexas.edu/users/chris/think/Cyclades/index.shtml|archive-date=2013-09-01}}</ref><ref>{{cite journal|first=Hubert|last=Zimmermann|title=The Cyclades Experience-Results and Impacts|journal=IFIP Congress 1977|pages=465–469|url=https://dblp.org/rec/conf/ifip/Zimmermann77|location=Toronto|date=August 1977}}</ref>

====DECnet====
[[DECnet]] is a suite of network protocols created by [[Digital Equipment Corporation]], originally released in 1975 in order to connect two [[PDP-11]] [[minicomputer]]s.<ref>{{citation |url=http://archive.computerhistory.org/resources/text/dec/dec.digital_1957_to_the_present_(1978).1957-1978.102630349.pdf |url-status=dead |archive-url=https://web.archive.org/web/20170630025909/http://archive.computerhistory.org/resources/text/dec/dec.digital_1957_to_the_present_(1978).1957-1978.102630349.pdf |archive-date=2017-06-30 |title=Digital Equipment Corporation, Nineteen Fifty-Seven to the Present |publisher=Digital Equipment Corporation |date=1978 |page=53}}</ref> It evolved into one of the first [[peer-to-peer]] network architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with three [[Abstraction layer|layers]], it later (1982) evolved into a seven-layer [[Open Systems Interconnection|OSI]]-compliant networking protocol. The DECnet protocols were designed entirely by Digital Equipment Corporation. However, DECnet Phase II (and later) were [[open standard]]s with published specifications, and several implementations were developed outside DEC, including one for [[Linux]].

====DDX-1====
DDX-1 was an experimental network from Nippon PTT. It mixed circuit switching and packet switching. It was succeeded by DDX-2.<ref>{{cite conference
|first= David C.
|last= Wood
|title= A Survey of the Capabilities of 8 Packet Switching Networks
|book-title= Proceedings of Symposium on Computer Networks
|year= 1975
|url= http://rogerdmoore.ca/PS/Wood.html#DDX
|access-date= 2020-03-13
|conference= 
|archive-date= 2020-08-06
|archive-url= https://web.archive.org/web/20200806042839/http://rogerdmoore.ca/PS/Wood.html#DDX
|url-status= dead
}}</ref>

==== EIN {{Anchor|European Informatics Network}} ====
The European Informatics Network (EIN), originally called COST 11, was a project beginning in 1971 to link networks in Britain, France, Italy, Switzerland and [[Euratom]]. Six other European countries also participated in the research on network protocols. Derek Barber directed the project, and [[Roger Scantlebury]] led the UK technical contribution; both were from [[National Physical Laboratory (United Kingdom)|NPL]].<ref>{{Cite journal|last=Barber|first=D L.|date=1975|title=Cost project 11|journal=ACM SIGCOMM Computer Communication Review|language=EN|volume=5|issue=3|pages=12–15|doi=10.1145/1015667.1015669|s2cid=28994436|doi-access=free}}</ref><ref>{{Cite book|last=Scantlebury|first=Roger|chapter-url=https://books.google.com/books?id=3EaeBQAAQBAJ|title=Communications Standards: State of the Art Report|publisher=Pergamon|year=1986|isbn=978-1-4831-6093-1|editor-last=Stokes|editor-first=A. V.|pages=203–216|language=en|chapter=X.25 - past, present and future}}</ref><ref>{{Cite web|url=https://www.computerhistory.org/revolution/networking/19/375/2062|title=EIN (European Informatics Network)|website=Computer History Museum|access-date=2020-02-05}}</ref><ref>{{cite web |title=European cooperation in the field of scientific and technical research (COST), 1971- |url=https://cordis.europa.eu/programme/id/IC-COST/fr}}</ref> The contract for its implementation was awarded to an Anglo French consortium led by the UK systems house [[Logica]] and Sesa and managed by [[Andrew Karney]]. Work began in 1973 and it became operational in 1976 including nodes linking the [[NPL network]] and [[CYCLADES]].<ref>{{Cite book|last=Abbate|first=Janet|url=https://books.google.com/books?id=E2BdY6WQo4AC&pg=PA125|title=Inventing the Internet|date=2000|publisher=MIT Press|isbn=978-0-262-51115-5|pages=125|language=en}}</ref> Barber proposed and implemented a mail protocol for EIN.<ref>Barber, D. L. A. and Laws, J.  (February 1979). “A basic mail scheme for EIN,” International Network Working Group (INWG), Note no. 192.</ref> The transport protocol of the EIN helped to launch the [[International Network Working Group|INWG]] and X.25 protocols.<ref>{{Cite book|last=Davies|first=Donald Watts|url=https://archive.org/details/computernetworks00davi|url-access=registration|title=Computer networks and their protocols|date=1979|publisher=John Wiley & Sons|pages=[https://archive.org/details/computernetworks00davi/page/464 464]|isbn=9780471997504}}</ref><ref>{{Cite book|last1=Hardy|first1=Daniel|url=https://books.google.com/books?id=dRhHPINWo2AC&pg=PT526|title=Networks: Internet, Telephony, Multimedia: Convergences and Complementarities|last2=Malleus|first2=Guy|date=2002|publisher=Springer Science & Business Media|isbn=978-3-540-00559-9|pages=505|language=en}}</ref><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=I actually set up the first meeting between John Wedlake of the British Post Office and [Rémi Després] of the French PTT which led to X25. There was a problem about virtual calls in EIN, so I called this meeting and that actually did in the end lead to X25.}}</ref> EIN was replaced by [[#Euronet|Euronet]] in 1979.<ref>{{Cite book|last=Beauchamp|first=K. G.|url=https://books.google.com/books?id=XbyrCAAAQBAJ&pg=PA55|title=Interlinking of Computer Networks: Proceedings of the NATO Advanced Study Institute held at Bonas, France, August 28 – September 8, 1978|date=2012-12-06|publisher=Springer Science & Business Media|isbn=978-94-009-9431-7|pages=55|language=en}}</ref>

====EPSS====
The Experimental Packet Switched Service (EPSS) was an experiment of the UK [[Post Office Telecommunications]]. It was the first [[public data network]] in the UK when it began operating in 1976.<ref>{{cite book|editor1-last=Davies|editor1-first=Howard|editor2-last=Bressan|editor2-first=Beatrice|title=A history of international research networking: the people who made it happen|date=2010|publisher=John Wiley & Sons|isbn=978-3527327102|page=2|url=https://books.google.com/books?id=DN-t8MpZ0-wC&pg=PA2}}</ref> [[Ferranti]] supplied the hardware and software. The handling of link control messages (acknowledgements and flow control) was different from that of most other networks.<ref>{{Cite web|last1=Smith|first1=Ed|last2=Miller|first2=Chris|last3=Norton|first3=Jim|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|journal=}}</ref><ref>{{cite conference
|first= Roy D.
|last= Bright
|author2= Smith, Michael A.
|title= EXPERIMENTAL PACKET SWITCHING PROJECT OF THE UK POST OFFICE
|book-title= Proceedings of the NATO Advanced Study Institute on Computer Communication Networks
|publisher= Noordhoff International Publishing
|location= Sussex, United Kingdom
|year= 1973
|pages= 435–44
|url= http://rogerdmoore.ca/PS/EPSSB.html
|conference= 
|access-date= 2013-08-30
|archive-date= 2013-10-20
|archive-url= https://web.archive.org/web/20131020142503/http://rogerdmoore.ca/PS/EPSSB.html
|url-status= dead
}}</ref><ref>{{cite conference
|first= DJ
|last= Pearson
|author2= Wilkin, D
|title= Some Design Aspects of a public packet switching network
|book-title= Proceedings of the 2nd ICCC 74
|pages= 199–213
|year= 1974
|url= http://rogerdmoore.ca/PS/EPSSFer/EF.html
|conference= 
|access-date= 2013-08-30
|archive-date= 2013-10-20
|archive-url= https://web.archive.org/web/20131020142152/http://rogerdmoore.ca/PS/EPSSFer/EF.html
|url-status= dead
}}</ref>

====GEIS====
As General Electric Information Services (GEIS), [[General Electric]] was a major international provider of information services. The company originally designed a telephone network to serve as its internal (albeit continent-wide) voice telephone network.

In 1965, at the instigation of Warner Sinback, a data network based on this voice-phone network was designed to connect GE's four computer sales and service centers (Schenectady, New York, Chicago, and Phoenix) to facilitate a computer time-sharing service.

After going international some years later, GEIS created a network data center near [[Cleveland]], Ohio. Very little has been published about the internal details of their network. The design was hierarchical with redundant communication links.<ref>{{cite journal |last= Schwartz |first= Mischa |author2= Boorstyn, Rober R. |author3= Pickholtz, Raymond L. |title= Terminal-Oriented Computer-Communication Networks |journal= Proceedings of the IEEE |volume= 60 |issue= 11 |pages= 1408–23 |date= November 1972 |url= http://rogerdmoore.ca/PS/TONET/TON.html#GEISCO |doi= 10.1109/proc.1972.8912 |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020092847/http://rogerdmoore.ca/PS/TONET/TON.html#GEISCO |url-status= dead |url-access= subscription }}</ref><ref>{{cite conference |first= Peter T. |last= Kirstein |title= A SURVEY OF PRESENT AND PLANNED GENERAL PURPOSE EUROPEAN DATA AND COMPUTER NETWORKS |book-title= Proceedings of the NATO Advanced Study Institute on Computer Communication Networks |publisher= Noordhoff International Publishing |location= Sussex, United Kingdom |year= 1973 |url= http://rogerdmoore.ca/PS/Kirs1973/Ki.html#GEISCO |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020092837/http://rogerdmoore.ca/PS/Kirs1973/Ki.html#GEISCO |url-status= dead }}</ref>

====IPSANET====
[[IPSANET]] was a semi-private network constructed by [[I. P. Sharp Associates]] to serve their time-sharing customers. It became operational in May 1976.<ref>{{cite web |url=http://rogerdmoore.ca/INF/ |title=IPSANET Documents |access-date=2020-10-22 |archive-date=2021-02-25 |archive-url=https://web.archive.org/web/20210225174511/http://www.rogerdmoore.ca/INF/ |url-status=dead }}</ref>

====IPX/SPX====
The [[IPX/SPX|Internetwork Packet Exchange]] (IPX) and Sequenced Packet Exchange (SPX) are [[Novell]] networking protocols from the 1980s derived from Xerox Network Systems' IDP and SPP protocols, respectively which date back to the 1970s. IPX/SPX was used primarily on networks using the [[NetWare|Novell NetWare operating systems]].<ref>{{cite web|url=http://support.novell.com/techcenter/articles/ana19980302.html|title=Maintaining IPX Compatibility During a Migration to TCP/IP on a NetWare Network|first=Rich|last=Lee|website=Novell|date=1 March 1998|access-date=3 September 2013}}</ref>

====Merit Network====
[[Merit Network]], an independent [[nonprofit organization]] governed by Michigan's public universities,<ref name="Merit">Merit receives administrative services under an agreement with the [[University of Michigan]].</ref> was formed in 1966 as the Michigan Educational Research Information Triad to explore computer networking between three of Michigan's public universities as a means to help the state's educational and economic development.<ref>{{citation |url=http://www.merit.edu/about/history/article.php |title=A Chronicle of Merit's Early History |archive-url=https://web.archive.org/web/20090207130720/http://merit.edu/about/history/article.php |archive-date=2009-02-07 |author=John Mulcahy |date=1989 |publisher=Merit Network |location=Ann Arbor, Michigan}}</ref> With initial support from the [[State of Michigan]] and the [[National Science Foundation]] (NSF), the packet-switched network was first demonstrated in December 1971 when an interactive host-to-host connection was made between the [[IBM mainframe]] systems at the [[University of Michigan]] in [[Ann Arbor]] and [[Wayne State University]] in [[Detroit]].<ref name="MeritTimeline1970-1979">{{citation |url=http://www.merit.edu/about/history/timeline_1970.php |title=Merit Network Timeline: 1970–1979 |archive-url=https://web.archive.org/web/20160101025735/http://www.merit.edu/about/history/timeline_1970.php |archive-date=2016-01-01 |publisher=Merit Network |location=Ann Arbor, Michigan}}</ref> In October 1972, connections to the [[Control Data Corporation|CDC]] mainframe at [[Michigan State University]] in [[East Lansing]] completed the triad. Over the next several years, in addition to host-to-host interactive connections, the network was enhanced to support terminal-to-host connections, host-to-host batch connections (remote job submission, remote printing, batch file transfer), interactive file transfer, gateways to the [[Tymnet]] and [[Telenet]] [[public data network]]s, X.25 host attachments, gateways to X.25 data networks, Ethernet attached hosts, and eventually [[TCP/IP]]; additionally, [[List of colleges and universities in Michigan#Public colleges and universities|public universities in Michigan]] joined the network.<ref name=MeritTimeline1970-1979/><ref name="MeritTimeline1980-1989">{{citation |url=http://www.merit.edu/about/history/timeline_1980.php |title=Merit Network Timeline: 1980–1989 |archive-url=https://web.archive.org/web/20160101025735/http://www.merit.edu/about/history/timeline_1980.php |archive-date=2016-01-01 |publisher=Merit Network |location=Ann Arbor, Michigan}}</ref> All of this set the stage for Merit's role in the [[NSFNET]] project starting in the mid-1980s.

====NPL====
[[Donald Davies]] of the [[National Physical Laboratory (United Kingdom)]] designed and proposed a national commercial data network based on packet switching in 1965.<ref>{{cite web |title=Donald Davies |url=http://www.thocp.net/biographies/davies_donald.htm |url-status=dead |archive-url=https://web.archive.org/web/20201105075754/http://www.thocp.net/biographies/davies_donald.htm |archive-date=2020-11-05 |access-date=2017-08-28 |work=thocp.net}}</ref><ref>{{cite web |title=Donald Davies |url=http://www.internethalloffame.org/inductees/donald-davies |work=internethalloffame.org}}</ref> The proposal was not taken up nationally but the following year, he designed a [[local network]] using  "interface computers", today known as [[Router (computing)|routers]], to serve the needs of NPL and prove the feasibility of packet switching.<ref>{{citation|last1=Pelkey|first1=James|title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968-1988|date=2007|chapter=NPL Network and Donald Davies 1966 - 1971|chapter-url=http://www.historyofcomputercommunications.info/Book/4/4.11-NPLNetworkDonaldDavies66-71.html|access-date=13 April 2016|archive-date=29 November 2020|archive-url=https://web.archive.org/web/20201129225124/http://www.historyofcomputercommunications.info/Book/4/4.11-NPLNetworkDonaldDavies66-71.html|url-status=dead}}</ref>

By 1968 Davies had begun building the [[NPL network]] to meet the needs of the multidisciplinary laboratory and prove the technology under operational conditions.<ref>{{cite conference |first= R. A. |last= Scantlebury |author2= Wilkinson, P.T. |title= The National Physical Laboratory Data Communications Network |book-title= Proceedings of the 2nd ICCC 74 |pages= 223–228 |year= 1974 |url= http://www.rogerdmoore.ca/PS/NPLPh/NPL1974A.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020140205/http://rogerdmoore.ca/PS/NPLPh/NPL1974A.html |url-status= dead }}</ref><ref name=Hempstead2005/><ref name="BBC Technology">{{cite news|url=https://news.bbc.co.uk/2/hi/technology/8331253.stm|title=Celebrating 40 years of the net|first=Mark|last=Ward|newspaper=BBC News|date=October 29, 2009}}</ref> In 1969, the NPL, followed by the ARPANET, were the first two networks to use packet switching.<ref>{{Cite journal |last1=John S |first1=Quarterman |last2=Josiah C |first2=Hoskins |date=1986 |title=Notable computer networks |journal=Communications of the ACM |language=EN |volume=29 |issue=10 |pages=932–971 |doi=10.1145/6617.6618 |s2cid=25341056 |quote=The first packet-switching network was implemented at the National Physical Laboratories in the United Kingdom. It was quickly followed by the ARPANET in 1969.|doi-access=free }}</ref><ref name="Haughney Dare-Bryan"/> By 1976, 12 computers and 75 terminal devices were attached,<ref>{{cite web|title=The National Physical Laboratory Data Communications Network|url=http://rogerdmoore.ca/PS/NPLPh/NPL1974A.html|access-date=5 September 2017|date=1974|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801152456/http://www.rogerdmoore.ca/PS/NPLPh/NPL1974A.html|url-status=dead}}</ref> and more were added until the network was replaced in 1986. NPL was the first to use high-speed links.<ref name=":3">{{Cite journal |last=Cambell-Kelly |first=Martin |date=1987 |title=Data Communications at the National Physical Laboratory (1965-1975) |url=https://archive.org/details/DataCommunicationsAtTheNationalPhysicalLaboratory |journal=Annals of the History of Computing |language=en |volume=9 |issue=3/4 |pages=221–247 |doi=10.1109/MAHC.1987.10023 |s2cid=8172150 |quote=Transmission of packets of data over the high-speed lines}}</ref><ref>{{Cite news |author=Guardian Staff |date=2013-06-25 |title=Internet pioneers airbrushed from history |language=en-GB |work=The Guardian |url=https://www.theguardian.com/technology/2013/jun/25/internet-pioneers-airbrushed-from-history |access-date=2020-07-31 |issn=0261-3077 |quote=This was the first digital local network in the world to use packet switching and high-speed links.}}</ref><ref name=":23">{{cite journal |last=Roberts |first=Lawrence G. |date=November 1978 |title=The evolution of packet switching |url=http://www.ece.ucf.edu/~yuksem/teaching/nae/reading/1978-roberts.pdf |journal=Proceedings of the IEEE |volume=66 |issue=11 |pages=1307–13 |doi=10.1109/PROC.1978.11141 |s2cid=26876676 |quote=Both Paul Baran and Donald Davies in their original papers anticipated the use of T1 trunks}}</ref>

====Octopus====<!-- [[Octopus network]] and similar redirect here -->
Octopus was a local network at [[Lawrence Livermore National Laboratory]]. It connected sundry hosts at the lab to interactive terminals and various computer peripherals including a bulk storage system.<ref>{{cite journal |last= Mendicino |first= Samuel F. |title= 1970 OCTOPUS: THE LAWRENCE RADIATION LABORATORY NETWORK |journal= Computer Networks |pages= 95–100 |publisher= Prentice-Hall Inc. |location= Englewood Cliffs, N.J. |year= 1972 |url= http://rogerdmoore.ca/PS/OCTOA/OCTO.html |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142202/http://rogerdmoore.ca/PS/OCTOA/OCTO.html |url-status= dead }}</ref><ref>{{cite web |last= Pehrson |first= David L. |title= AN ENGINEERING VIEW OF THE LRL OCTOPUS COMPUTER NETWORK |year= 1970 |url= http://www.computer-history.info/Page4.dir/pages/Octopus.dir/index.html}}</ref><ref>{{cite web |last= Fletcher |first= John G. |title= Principles of Design in the Octopus Computer network |year= 1975 |url= http://portal.acm.org/citation.cfm?id=810357}}</ref>

====Philips Research====
[[Philips]] Research Laboratories in [[Redhill, Surrey]] developed a packet switching network for internal use. It was a datagram network with a single switching node.<ref>{{cite journal |last= Burnett |first= D.J. |author2= Sethi, H.R. |title= Packet Switching at Philips Research Laboratories |journal= Computer Networks |volume= 1 |issue= 6 |pages= 341–348 |url= http://rogerdmoore.ca/PS/NPLPh/PhilipsA.html |doi= 10.1016/0376-5075(77)90010-1 |year= 1977 |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142510/http://rogerdmoore.ca/PS/NPLPh/PhilipsA.html |url-status= dead |url-access= subscription }}</ref>

====PUP====
[[PARC Universal Packet]] (PUP or Pup) was one of the two earliest [[internetworking]] [[protocol suite]]s; it was created by researchers at [[Xerox PARC]] in the mid-1970s. The entire suite provided [[routing]] and packet delivery, as well as higher level functions such as a [[reliable byte stream]], along with numerous applications. Further developments led to [[Xerox Network Systems]] (XNS).<ref>{{cite journal |author1= David R. Boggs |author2-link= John F. Shoch |author2= John F. Shoch |author3= Edward A. Taft |author4-link= Robert M. Metcalfe |author4= Robert M. Metcalfe |s2cid= 62684407 |title= Pup: An Internetwork Architecture |journal= IEEE Transactions on Communications |volume=28 |issue=4 |pages=612–624 |date= April 1980 |doi= 10.1109/TCOM.1980.1094684|author1-link= David R. Boggs }}</ref>

====RCP====
RCP was an experimental network created by the [[Postes, Télégraphes et Téléphones (France)|French PTT]]. It was used to gain experience with packet switching technology before the specification of the [[Transpac (data network)|TRANSPAC]] public network was frozen. RCP was a [[virtual circuit|virtual-circuit]] network in contrast to CYCLADES which was based on [[datagram]]s. RCP emphasised terminal-to-host and terminal-to-terminal connection; CYCLADES was concerned with host-to-host communication. RCP influenced the X.25 specification, which was deployed on TRANSPAC and other public data networks.<ref name="RCP">{{cite conference |first= R. |last= Després |author-link= Rémi Després |title= RCP, THE EXPERIMENTAL PACKET-SWITCHED DATA TRANSMISSION SERVICE OF THE FRENCH PTT |book-title= Proceedings of ICCC 74 |pages= 171–85 |year= 1974 |url= http://rogerdmoore.ca/PS/RCPDEP/RD.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142207/http://rogerdmoore.ca/PS/RCPDEP/RD.html |url-status= dead }}</ref><ref>{{cite conference |first= A. |last= Bache |author2= Matras, Y. |title= Fundamental Choices in the Development of RCP, the Experimental Packet-Switching Data Transmission Service of the French PTT |book-title= Proceedings of ICCC 76 |pages= 311–16 |year= 1976 |url= http://rogerdmoore.ca/PS/RCPBAC/RB.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142631/http://rogerdmoore.ca/PS/RCPBAC/RB.html |url-status= dead }}</ref><ref>{{cite conference |first= A. |last= Bache |author2= L. Guillou |author3= H. Layec |author4= B. Long |author5= Y. Matras |title= RCP, the Experimental Packet-Switched Data Transmission Service of the French PTT: History, Connections, Control |book-title= Proceedings of ICCC 76 |year= 1976 |url= http://rogerdmoore.ca/PS/RCPHCC/RH.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142520/http://rogerdmoore.ca/PS/RCPHCC/RH.html |url-status= dead }}</ref>

====RETD====
Red Especial de Transmisión de Datos (RETD) was a network developed by [[Compañía Telefónica Nacional de España]]. It became operational in 1972 and thus was the first public network.<ref>{{cite conference |first= G. |last= Alarcia |author2= Herrera, S. |title= C.T.N.E.'s Packet Switching Network. Its Applications |book-title= Proceedings of 2nd ICCC 74 |pages= 163–170 |year= 1974 |url= http://rogerdmoore.ca/PS/CTNEA/CTA.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020141839/http://rogerdmoore.ca/PS/CTNEA/CTA.html }}</ref><ref>{{cite conference |first= L. |last= Cuenca |title= A Public Packet Switching Data Communications Network: Eight Years of Operating Experience |book-title= Conference Record of ICC 80 |pages= 39.3.1–39.3.5 |publisher= IEEE |year= 1980 |url= http://rogerdmoore.ca/PS/CTNEC1.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020140055/http://rogerdmoore.ca/PS/CTNEC1.html |url-status= dead }}</ref><ref>{{cite conference |first= Luis |last= Lavandera |title= Architecture, Protocols and Performance of RETD |book-title= Conference Record of ICC 80 |pages= 28.4.1–28.4.5 |publisher= IEEE |year= 1980 |url= http://rogerdmoore.ca/PS/RETDB.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142212/http://rogerdmoore.ca/PS/RETDB.html |url-status= dead }}</ref><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>

====SCANNET====
"The experimental packet-switched Nordic telecommunication network SCANNET was implemented in Nordic technical libraries in the 1970s, and it included first Nordic electronic journal Extemplo. Libraries were also among first ones in universities to accommodate microcomputers for public use in the early 1980s."<ref>{{cite conference |title=The Role of Libraries in Information Management in Finnish University Setting |first=Arja-Riitta |last=Haarala |doi= 10.18452/1040 |year=2001 |book-title = Proceedings of the 7th International Conference of European University Information Systems}}</ref>

====SITA HLN====
[[SITA (IT company)|SITA]] is a consortium of airlines. Its High Level Network (HLN) became operational in 1969. Although organised to act like a packet-switching network,<ref name="Roberts1978" /> it still used [[message switching]].<ref>{{cite conference |last=Chretien |first=G.J. |author2=Konig, W.M. |author3=Rech, J.H. |date=1973 |title=The SITA Network |url=http://rogerdmoore.ca/PS/SITAB.html |location=Sussex, United Kingdom |publisher=Noordhoff International Publishing |pages=373–396 |archive-url=https://web.archive.org/web/20131020140241/http://rogerdmoore.ca/PS/SITAB.html |archive-date=2013-10-20 |book-title=Proceedings of the NATO Advanced Study Institute on Computer Communication Networks |url-status=dead}}</ref><ref name=":25">{{Cite web |title=Interview of Donald Davies |url=http://archive.computerhistory.org/resources/access/text/2017/11/102738594-05-01-acc.pdf}}</ref> As with many non-academic networks, very little has been published about it.

====SRCnet/SERCnet====

A number of computer facilities serving the [[Science Research Council]] (SRC) community in the United Kingdom developed beginning in the early 1970s. Each had their own star network ([[University of London Computer Centre|ULCC London]], UMRCC Manchester, [[Rutherford Appleton Laboratory]]). There were also regional networks centred on Bristol (on which work was initiated in the late 1960s) followed in the mid-late 1970s by Edinburgh, the Midlands and Newcastle. These groups of institutions [[shared resource]]s to provide better computing facilities than could be afforded individually. The networks were each based on one manufacturer's standards and were mutually incompatible and overlapping.<ref>{{Cite thesis |last=Rutter |first=Dorian |title=From Diversity to Convergence: British Computer Networks and the Internet, 1970-1995 |date=2005 |degree=Computer Science |publisher=The University of Warwick |url=http://wrap.warwick.ac.uk/1197/1/WRAP_THESIS_Rutter_2005.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://wrap.warwick.ac.uk/1197/1/WRAP_THESIS_Rutter_2005.pdf |archive-date=2022-10-10 |url-status=live}}</ref><ref>{{Cite journal |last=Powell |first=Kit |date=1980-07-01 |title=Evolution of networks using standard protocols |url=https://dx.doi.org/10.1016/0140-3664%2880%2990069-9 |journal=Computer Communications |language=en |volume=3 |issue=3 |pages=117–122 |doi=10.1016/0140-3664(80)90069-9 |issn=0140-3664|url-access=subscription }}</ref><ref name="ieee-kirstein">{{cite journal |last=Kirstein |first=Peter T. |date=Jan–Mar 1999 |title=Early Experiences with the ARPANET and INTERNET in the UK |url=http://nrg.cs.ucl.ac.uk/mjh/kirstein-arpanet.pdf |journal=IEEE Annals of the History of Computing |volume=21 |issue=1 |doi=10.1109/85.759368 |access-date=18 May 2020 |archive-date=10 August 2017 |archive-url=https://web.archive.org/web/20170810133640/http://nrg.cs.ucl.ac.uk/mjh/kirstein-arpanet.pdf |url-status=dead }}</ref> In 1981, the SRC was renamed the [[Science and Engineering Research Council]] (SERC). In the early 1980s a standardisation and interconnection effort started, hosted on an expansion of the SERCnet research network and based on the [[Coloured Book protocols]], later evolving into [[JANET]].<ref name=":02">{{Cite journal |last=Wells |first=Mike |date=1988-11-01 |title=JANET-the United Kingdom Joint Academic Network |journal=Serials |language=en |volume=1 |issue=3 |pages=28–36 |doi=10.1629/010328 |issn=1475-3308 |doi-access=free}}</ref><ref>{{cite conference |last=Reid |first=Jim |date=3 April 2007 |title=The Good Old Days: Networking in UK Academia ~25 Years Ago |url=http://www.uknof.com/uknof7/Reid-History.pdf |location=Manchester |access-date=16 April 2008 |book-title=UKNOF7 |archive-date=28 May 2008 |archive-url=https://web.archive.org/web/20080528040321/http://www.uknof.com/uknof7/Reid-History.pdf |url-status=dead }}</ref><ref name=":2">{{Cite web |title=6th UK Network Operators' Forum Meeting Agenda |url=https://www.uknof.org.uk/uknof6/ |access-date=2020-02-12 |website=www.uknof.org.uk |quote=See "15:00 Starting the Commercial Internet in the UK (Peter Houlder)" |archive-date=2007-06-21 |archive-url=https://web.archive.org/web/20070621051719/http://www.uknof.org.uk/uknof6/ |url-status=dead }}</ref>

====Systems Network Architecture====
[[Systems Network Architecture]] (SNA) is [[IBM]]'s proprietary networking architecture created in 1974. An IBM customer could acquire hardware and software from IBM and lease private lines from a common carrier to construct a private network.<ref>{{cite conference |first= R.J. |last= Sundstrom |author2= G.D. Schultz |title= 1980 SNA'S First Six Years: 1974-1980 |book-title= Proceedings of 5th ICCC 80 |pages= 578–585 |date= 1980 |url= http://rogerdmoore.ca/PS/SNA6Y/SNA6.html |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142728/http://rogerdmoore.ca/PS/SNA6Y/SNA6.html |url-status= dead }}</ref>

====Telenet====
[[Telenet]] was the first FCC-licensed [[public data network]] in the United States. Telenet was incorporated in 1973 and started operations in 1975. It was founded by [[Bolt Beranek & Newman]] with [[Lawrence Roberts (scientist)|Larry Roberts]] as CEO as a means of making packet switching technology public. Telenet initially used a proprietary [[Virtual circuit]] host interface, but changed it to X.25 and the terminal interface to X.29 after their standardization in [[CCITT]].<ref name=":2A">{{cite journal|last1=Roberts|first1=Dr. Lawrence G.|date=November 1978|title=The Evolution of Packet Switching|url=http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf|journal=IEEE Invited Paper|access-date=September 10, 2017|archive-date=December 31, 2018|archive-url=https://web.archive.org/web/20181231092936/http://www.ismlab.usf.edu/dcom/Ch10_Roberts_EvolutionPacketSwitching_IEEE_1978.pdf|url-status=dead}}</ref> It went public in 1979 and was then sold to GTE.<ref>{{cite journal|title=Electronic post for switching data|first=Timothy|last=Johnson|journal=New Scientist|date=May 13, 1976}}</ref><ref>{{cite journal|doi=10.1109/MCOM.2012.6194380|last1=Mathison|first1=S.L.|last2=Roberts|first2=L.G.|last3=Walker|first3=P.M.|title=The history of telenet and the commercialization of packet switching in the U.S.|journal=IEEE Communications Magazine|date=May 2012|volume=50|issue=5|pages=28–45|bibcode=2012IComM..50e..28M |s2cid=206453987}}</ref>

====Tymnet====
[[Tymnet]] was an international data communications network headquartered in San Jose, CA. In 1969, it began install a network based on minicomputers to connect timesharing terminals to its central computers. The network used store-and-forward and voice-grade lines. Routing was not distributed, rather it was established by a central supervisor on a call-by-call basis.<ref name="Roberts1978" />

===X.25 era===
{{See also|Public data network}}
[[File:CCITT SGVII X25 Advocates.jpg|thumb|CCITT SGVII X25 Advocates]]
There were two kinds of X.25 networks. Some such as [[DATAPAC]] and [[Transpac (data network)|TRANSPAC]] were initially implemented with an X.25 external interface. Some older networks such as TELENET and TYMNET were modified to provide an X.25 host interface in addition to older host connection schemes. DATAPAC was developed by [[Bell-Northern Research]] which was a joint venture of [[Bell Canada]] (a common carrier) and [[Northern Telecom]] (a telecommunications equipment supplier). Northern Telecom sold several DATAPAC clones to foreign PTTs including the [[Deutsche Bundespost]]. [[X.75]] and [[X.121]] allowed the interconnection of national X.25 networks.

====AUSTPAC====
[[AUSTPAC]] was an Australian public X.25 network operated by [[Telstra]]. Established by Telstra's predecessor Telecom Australia in the early 1980s, AUSTPAC was Australia's first public packet-switched data network and supported applications such as on-line betting, financial applications—the [[Australian Taxation Office]] made use of AUSTPAC—and remote terminal access to academic institutions, who maintained their connections to AUSTPAC up until the mid-late 1990s in some cases. Access was via a dial-up terminal to a [[Packet Assembler/Disassembler|PAD]], or, by linking a permanent X.25 node to the network.<ref name="Andrew Colley">{{cite web | url=https://www.zdnet.com/home-and-office/networking/telstra-drops-austpac-reaches-for-finance-market/ | title=Telstra drops Austpac; reaches for finance market | date=28 January 2004 | access-date=21 December 2018 | author= Andrew Colley| website=[[ZDNet]] }}</ref>

====ConnNet====
[[ConnNet]] was a network operated by the [[Southern New England Telephone Company]] serving the state of Connecticut.<ref>{{Cite book|url=https://books.google.com/books?id=3ufUXLhZHLoC&q=ConnEct+was+a+packet-switched+data+network+operated+by+the+Southern+New+England+Telephone+Company+serving+the+state+of+Connecticut&pg=PA40|title=Straight To The Point - Networking|last=Maidasani|first=Dinesh|date=June 2009|publisher=Laxmi Publications Pvt Limited|isbn=9788131805299}}</ref><ref>{{cite book |last1=Smith |first1=Christopher A. |title=Technology for Disabled Persons: Conference Papers, Discovery '84, October 1-3, 1984, Chicago, Illinois |date=1985 |publisher=Materials Development Center, Stout Vocational Rehabilitation Institute, University of Wisconsin-Stout |isbn=978-0-916671-61-7 |page=195 |url=https://books.google.com/books?id=Vx7uAAAAMAAJ |access-date=12 January 2022 |language=en}}</ref> Launched on March 11, 1985, it was the first local public packet-switched network in the United States.<ref>{{Cite book|last1=Rucker|first1=Chauncy N.|url=https://eric.ed.gov/?id=ED286327|title=Establishing a Computer Network for Connecticut|last2=And Others|date=1985|language=en}}</ref>

====Datanet 1====
Datanet 1 was the public switched data network operated by the Dutch PTT Telecom (now known as [[KPN]]). Strictly speaking Datanet 1 only referred to the network and the connected users via [[leased line]]s (using the [[X.121]] DNIC 2041), the name also referred to the public [[Packet Assembler/Disassembler|PAD]] service ''Telepad'' (using the DNIC 2049). And because the main [[Videotex]] service used the network and modified PAD devices as infrastructure the name Datanet 1 was used for these services as well.<ref name="dn1descr">{{cite web|first=H.J.|last=Steneker|url=http://alexandria.tue.nl/extra1/afstversl/E/354398.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://alexandria.tue.nl/extra1/afstversl/E/354398.pdf |archive-date=2022-10-10 |url-status=live|title=Graduation Report on X.25 data services in GSM network|website=Electrical Engineering - [[Eindhoven University of Technology|TUE]]|date=16 May 1991|page=20|access-date=15 June 2011}}</ref>

====DATAPAC====
[[DATAPAC]] was the first operational X.25 network (1976).<ref>{{cite magazine |last=Rybczynski |first=Tony |date=11 December 2009 |title=Commercialization of packet switching (1975-1985): A Canadian perspective [History of Communications] |url=https://ieeexplore.ieee.org/document/5350364 |magazine=IEEE Communications Magazine  |access-date=12 January 2022|doi=10.1109/MCOM.2009.5350364|volume=47|issue=12|pages=26–31 }}</ref> It covered major Canadian cities and was eventually extended to smaller centers.{{Citation needed|date=February 2011}}

====Datex-P====
Deutsche Bundespost operated the '''Datex-P''' national network in Germany. The technology was acquired from Northern Telecom.<ref>{{Cite book|last=Parodi|first=Roberto|url=https://books.google.com/books?id=wxixcg3JSbwC&q=packet+switching+The+technology+was+acquired+from+Northern+Telecom&pg=RA1-PA539|title=Towards a New World in Computer Communication: Eleventh International Conference on Computer Communication, Genova, Italy, 1992 : Proceedings of the Conference|date=1992|publisher=IOS Press|isbn=978-90-5199-110-9|language=en}}</ref>

==== Eirpac ====
[[Eirpac]] is the Irish public switched data network supporting X.25 and [[X.28]]. It was launched in 1984, replacing Euronet. Eirpac is run by [[Eircom]].<ref>{{cite book
|title=Telecommunications Directory
|year=2000
|publisher=Gale Research
|isbn=978-0-7876-3352-3
|page=593
}}</ref><ref>{{cite book
|author=Gareth Locksley
|title=The Single European Market and the Information and Communication Technologies
|year=1990
|publisher=Belhaven Press
|isbn=978-1-85293-101-8
|page=194
}}</ref><ref>{{cite web
|url=https://www.casemine.com/judgement/uk/5da04a364653d0053b353082
|title=Eircom Plc and the Department of Agriculture and Food; Mr Mark Henry and the Department of Agriculture and Food; Eircom Plc and the Department of Finance and Eircom Plc and Office of the Revenue Commissioners. {{!}} [2000] IEIC 98114 {{!}} Irish Information Commissioner {{!}} Judgment {{!}} Law {{!}} CaseMine
|access-date=2022-06-22
|archive-url=https://web.archive.org/web/20220621224408/https://www.casemine.com/judgement/uk/5da04a364653d0053b353082
|archive-date=2022-06-21
|url-status=live}}</ref>

====Euronet====
Nine member states of the [[European Economic Community]] contracted with [[Logica]] and the French company SESA to set up a joint venture in 1975 to undertake the ''Euronet'' development, using X.25 protocols to form virtual circuits. It was to replace EIN and established a network in 1979 linking a number of European countries until 1984 when the network was handed over to national PTTs.<ref>{{cite journal|title=Origins, development and future of the Euronet|date=1977-12-31|publisher=Emeraldinsight.com|doi=10.1108/eb046759|last1 = Dunning|first1 = A.J.|journal = Program|volume = 11|issue = 4|pages = 145–155}}</ref><ref>{{Cite journal|last=Kerssens|first=Niels|title=Rethinking legacies in internet history: Euronet, lost (inter)networks, EU politics|journal=Internet Histories|pages=32–48|doi=10.1080/24701475.2019.1701919|issn=2470-1475|year=2020|volume=4|doi-access=free}}</ref>

====HIPA-NET====
[[Hitachi]] designed a private network system for sale as a turnkey package to multi-national organizations.{{when|date=July 2022}} In addition to providing X.25 packet switching, message switching software was also included. Messages were buffered at the nodes adjacent to the sending and receiving terminals. Switched virtual calls were not supported, but through the use of ''logical ports'' an originating terminal could have a menu of pre-defined destination terminals.<ref>{{cite conference |first= K. |last= Tomaru |author2= T. Kato |author3= S.I. Yamaguchi |title= A Private Packet Network and Its Application in A Worldwide Integrated Communication Network |book-title= Proceedings of ICCC '80 |pages= 517–22 |year= 1980 |url= http://rogerdmoore.ca/PS/HIPA/HIA.html |conference=  |access-date= 2013-08-30 |archive-date= 2013-10-20 |archive-url= https://web.archive.org/web/20131020142157/http://rogerdmoore.ca/PS/HIPA/HIA.html |url-status= dead }}</ref>

====Iberpac====
[[Iberpac]] is the Spanish public packet-switched network, providing X.25 services. It was based on RETD which was operational since 1972. Iberpac was run by [[Telefonica]].<ref>{{Citation|title=El Desarrollo de la Red Publica de Datos en Espana (1971-1991): Un Caso de Avance Technologico en Condiciones Adversas|last=Infante|first=Jorge|url=http://www.coit.es/foro/pub/ficheros/infante_fd0e6980.pdf|archive-url=https://web.archive.org/web/20100405211910/http://www.coit.es/foro/pub/ficheros/infante_fd0e6980.pdf|archive-date=2010-04-05|url-status=dead}}</ref>

====IPSS====
In 1978, X.25 provided the first international and commercial packet-switching network, the [[International Packet Switched Service]] (IPSS).

====JANET====
[[JANET]] was the UK academic and research network, linking all universities, higher education establishments, and publicly funded research laboratories following its launch in 1984.<ref>{{cite web|title=1984-2014: 30 years of the Janet network|url=https://www.jisc.ac.uk/sites/default/files/janet-news-24-pull-out-april-2014.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://www.jisc.ac.uk/sites/default/files/janet-news-24-pull-out-april-2014.pdf |archive-date=2022-10-10 |url-status=live|publisher=Disc|access-date=23 September 2017}}</ref> The X.25 network, which used the [[Coloured Book protocols]], was based mainly on [[GEC 4000 series]] switches, and ran X.25 links at up to {{nowrap|8 Mbit/s}} in its final phase before being converted to an IP-based network in 1991. The JANET network grew out of the 1970s SRCnet, later called SERCnet.<ref>{{Cite journal|last=Wells|first=Mike|date=1988-11-01|title=JANET-the United Kingdom Joint Academic Network|journal=Serials|language=en|volume=1|issue=3|pages=28–36|doi=10.1629/010328|issn=1475-3308|doi-access=free}}</ref>

====PSS====
[[Packet Switch Stream]] (PSS) was the [[Post Office Telecommunications]] (later to become [[British Telecom]]) national X.25 network with a [[data network identification code|DNIC]] of 2342. British Telecom renamed PSS Global Network Service (GNS), but the PSS name has remained better known. PSS also included public dial-up PAD access, and various InterStream gateways to other services such as Telex.

==== REXPAC ====
REXPAC was the nationwide experimental packet switching data network in Brazil, developed by the research and development center of [[Telebrás]], the state-owned public telecommunications provider.<ref>{{Cite web |date=2017-06-09 |title=REXPAC-A Brazilian Packet Switching Data Network |url=http://www.rogerdmoore.ca/PS/REXP/REX.html |access-date=2022-08-30 |archive-url=https://web.archive.org/web/20170609193539/http://www.rogerdmoore.ca/PS/REXP/REX.html |archive-date=2017-06-09 }}</ref>

====SITA Data Transport Network====
[[SITA (IT company)|SITA]] is a consortium of airlines. Its Data Transport Network 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> As with many non-academic networks, very little has been published about it.

====TRANSPAC====
[[Transpac (data network)|TRANSPAC]] was the national X.25 network in France.<ref name="Transpac paper">{{citation | last1=Schwartz | first1=Mischa | last2=Després | first2=Rémi |language=en | title=X.25 Virtual Circuits - TRANSPAC in France - Pre-Internet Data Networking | journal=IEEE Communications Magazine | date=2010 | volume=48 | issue=11 | page=40 | doi=10.1109/MCOM.2010.5621965 | bibcode=2010IComM..48k..40S | s2cid=23639680}}</ref> It was developed locally at about the same time as DATAPAC in Canada. The development was done by the French PTT and influenced by its preceding experimental network [[Packet switching#RCP|RCP]].<ref name="Transpac choices">{{cite web|language=en|url=https://www.dropbox.com/s/v43kuy5xwasg2l7/ISS%2076%20-%20Discussion%20of%20Technical%20Choices%20made%20for%20Transpac.pdf?dl=0|title=Discussion of Technical Choices made for TRANSPAC}}</ref> It began operation in 1978, and served commercial users and, after [[Minitel]] began, consumers.<ref name="epstein19860309">{{Cite news |url=https://www.nytimes.com/1986/03/09/magazine/et-voila-le-minitel.html?pagewanted=all |title=Et Voila! Le Minitel |last=Epstein |first=Nadine |date=1986-03-09 |work=The New York Times}}</ref>

====Tymnet====
[[Tymnet]] utilized virtual call packet switched technology including X.25, SNA/SDLC, BSC and ASCII interfaces to connect host computers (servers) at thousands of large companies, educational institutions, and government agencies. Users typically connected via dial-up connections or dedicated [[asynchronous serial]] connections. The business consisted of a large public network that supported dial-up users and a private network business that allowed government agencies and large companies (mostly banks and airlines) to build their own dedicated networks. The private networks were often connected via gateways to the public network to reach locations not on the private network. Tymnet was also connected to dozens of other public networks in the U.S. and internationally via X.25/X.75 gateways.<ref>{{cite conference |last=TYMES |first=LA ROY W. |title=TYMNET &mdash; A terminal oriented communication network |url=http://rogerdmoore.ca/PS/TYMNET/TY.html |conference= |volume=38 |pages=211–16 |archive-url=https://web.archive.org/web/20130509125506/http://rogerdmoore.ca/PS/TYMNET/TY.html |archive-date=2013-05-09 |access-date=2013-08-30 |book-title=Proceedings of the SJCC 1971 |url-status=dead}}</ref><ref>{{cite journal |last=TYMES |first=LA ROY W. |date=April 1981 |title=Routing and Flow Control in TYMNET |url=http://www.rogerdmoore.ca/PS/TYMFlow/TF.html |url-status=dead |journal=IEEE Transactions on Communications |volume=COM-29 |issue=4 |pages=392–98 |doi=10.1109/tcom.1981.1095020 |archive-url=https://web.archive.org/web/20131020140315/http://rogerdmoore.ca/PS/TYMFlow/TF.html |archive-date=2013-10-20 |access-date=2013-08-30|url-access=subscription }}</ref>

==== UNINETT ====
UNINETT was a wide-area Norwegian packet-switched network established through a joint effort between Norwegian universities, research institutions and the Norwegian Telecommunication administration. The original network was based on X.25; Internet protocols were adopted later.<ref>{{Cite web |date=2017-06-09 |title=UNINETT Packet Switched Network Connecting Universities and Research Institutes in Norway |url=http://www.rogerdmoore.ca/PS/UNINTT/UNI.html |access-date=2022-08-30 |archive-url=https://web.archive.org/web/20170609203023/http://www.rogerdmoore.ca/PS/UNINTT/UNI.html |archive-date=2017-06-09 }}</ref>

====VENUS-P====
VENUS-P was an international X.25 network that operated from April 1982 through March 2006. At its subscription peak in 1999, VENUS-P connected 207 networks in 87 countries.<ref>{{cite web|url=http://www.kddi.com/english/corporate/news_release/2005/1109/|title=KDDI to Close VENUS-P International Public Data Communications Service|archive-url=https://archive.today/20130904020803/http://www.kddi.com/english/corporate/news_release/2005/1109/|archive-date=2013-09-04|website=KDDI|date=9 November 2005|access-date=3 September 2013}}</ref>

====XNS====
[[Xerox Network Systems]] (XNS) was a [[protocol suite]] promulgated by [[Xerox]], which provided [[routing]] and packet delivery, as well as higher-level functions such as a [[reliable stream]], and [[remote procedure call]]s. It was developed from [[PARC Universal Packet]] (PUP).<ref>{{cite web |year=1981 |title=Xerox System Integration Standard - Internet Transport Protocols |url=http://code.msgilligan.com/2012/07/xerox-system-integration-standard.html |website=Xerox |location=Stamford}}</ref><ref>{{cite book |title=AIX Version 4.3 Communications Programming Concepts |date=October 1997 |publisher=International Business Machines |chapter=Chapter 12: Xerox Network Systems |chapter-url=http://ics.upjs.sk/~novotnyr/home/programovanie/c/books/cpc/ch12_xns.htm}}</ref>

===Internet era===
{{Internet}}
When [[Internet]] connectivity was made available to anyone who could pay for an [[Internet service provider]] subscription, the distinctions between national networks blurred. The user no longer saw network identifiers such as the DNIC. Some older technologies such as [[circuit switching]] have resurfaced with new names such as [[fast packet switching]]. Researchers have created some experimental networks to complement the existing Internet.<ref name="Mike C. Smith">{{cite web | url=https://www.networkworld.com/article/964249/what-is-dedicated-internet-access.html | title=What is Dedicated Internet Access? | date=7 September 2017 | access-date=21 December 2018 | author=Mike C. Smith | archive-date=21 December 2018 | archive-url=https://web.archive.org/web/20181221184051/https://www.networkworld.com/article/3221478/internet/what-is-dedicated-internet-access.html | url-status=live }}</ref>

====CSNET====
The [[Computer Science Network]] (CSNET) was a computer network funded by the NSF that began operation in 1981. Its purpose was to extend networking benefits for [[computer science]] departments at academic and research institutions that could not be directly connected to [[ARPANET]] due to funding or authorization limitations. It played a significant role in spreading awareness of, and access to, national networking and was a major milestone on the path to the development of the global [[Internet]].<ref name="nsf">{{Cite web |title= The Internet—From Modest Beginnings |work= NSF website |url= https://www.nsf.gov/about/history/nsf0050/internet/modest.htm |access-date= September 30, 2011 |url-status= dead |archive-url= https://web.archive.org/web/20110828125922/https://www.nsf.gov/about/history/nsf0050/internet/modest.htm |archive-date= August 28, 2011 }}</ref><ref>{{Cite journal |title= History and overview of CSNET |author= Douglas Comer |journal= Communications |date= October 1983 |volume= 26 |number= 10 |doi= 10.1145/358413.358423 |pages=747–753|s2cid= 11943330 |author-link= Douglas Comer |doi-access= free }}</ref>

====Internet2====
[[Internet2]] is a not-for-profit United States [[computer network]]ing [[consortium]] led by members from the research and education communities, industry, and government.<ref>{{cite web|url=http://internet2.edu/about|title=About Internet2|access-date=2009-06-26}}</ref> The Internet2 community, in partnership with [[Qwest]], built the first Internet2 Network, called [[Abilene Network|Abilene]], in 1998 and was a prime investor in the [[National LambdaRail]] (NLR) project.<ref>{{cite web |url=http://news.com.com/Optical%20networking%20The%20next%20generation/2100-1033-5403589.html?part=dht&tag=ntop&tag=nl.e703 |title=Optical networking: The next generation |first=Marguerite |last=Reardon |website=CNET |date=October 11, 2004 |archive-url=https://archive.today/20120710234213/http://news.com.com/Optical%20networking%20The%20next%20generation/2100-1033-5403589.html?part=dht&tag=ntop&tag=nl.e703 |archive-date=10 July 2012 |url-status=dead}}</ref> In 2006, Internet2 announced a partnership with [[Level 3 Communications]] to launch a brand new nationwide network, boosting its capacity from 10 to {{nowrap|100 Gbit/s}}.<ref>{{cite news|url=https://www.usatoday.com/tech/news/techinnovations/2007-10-11-faster-internet2_N.htm|title=Speedy Internet2 gets 10x boost|first=Anick|last=Jesdanun|newspaper=USA Today|date=October 11, 2007|access-date=26 June 2009}}</ref> In October, 2007, Internet2 officially retired Abilene and now refers to its new, higher capacity network as the Internet2 Network.

====NSFNET====
[[File:NSFNET-traffic-visualization-1991.jpg|thumb|right|NSFNET Traffic 1991, NSFNET backbone nodes are shown at the top, regional networks below, traffic volume is depicted from purple (zero bytes) to white (100 billion bytes), visualization by [[National Center for Supercomputing Applications|NCSA]] using traffic data provided by the [[Merit Network]].]]

The [[National Science Foundation Network]] (NSFNET) was a program of coordinated, evolving projects sponsored by the NSF beginning in 1985 to promote advanced research and education networking in the United States.<ref>{{cite web|url=http://www.nsfnet-legacy.org/|title=NSFNET: The Partnership That Changed The World|date=November 2007}}</ref> NSFNET was also the name given to several nationwide backbone networks, operating at speeds of {{nowrap|56 kbit/s}}, {{nowrap|1.5 Mbit/s}} (T1), and {{nowrap|45 Mbit/s}} (T3), that were constructed to support NSF's networking initiatives from 1985 to 1995. Initially created to link researchers to the nation's NSF-funded supercomputing centers, through further public funding and private industry partnerships it developed into a major part of the [[Internet backbone]].

====NSFNET regional networks====
In addition to the five NSF supercomputer centers, NSFNET provided connectivity to eleven regional networks and through these networks to many smaller regional and campus networks in the United States. The NSFNET regional networks were:<ref name=ConneXions-April1996>{{cite web|url=http://www.merit.edu/research/nsfnet_article.php|title=Retiring the NSFNET Backbone Service: Chronicling the End of an Era|archive-url=https://web.archive.org/web/20130817124939/http://merit.edu/research/nsfnet_article.php|archive-date=2013-08-17|first1=Susan R.|last1=Harris|first2=Elise|last2=Gerich|website=ConneXions|volume=10|issue=4|date=April 1996}}</ref><ref>{{cite web|url=http://www.nsfnet-legacy.org/archives/06--Community.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.nsfnet-legacy.org/archives/06--Community.pdf |archive-date=2022-10-10 |url-status=live|title=NSFNET: The Community|first=Doug|last=Gale|website=NSFNET: The Partnership That Changed The World|date=29 November 2007}}</ref>
*BARRNet, the Bay Area Regional Research Network in [[Palo Alto, California]];
*[[CERFnet]], California Education and Research Federation Network in [[San Diego, California]], serving California and Nevada;
*CICNet, the [[Committee on Institutional Cooperation]] Network via the Merit Network in [[Ann Arbor, Michigan]] and later as part of the T3 upgrade via [[Argonne National Laboratory]] outside of [[Chicago]], serving the [[Big Ten]] Universities and the [[University of Chicago]] in Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin;
*[[Merit Network|Merit/MichNet]] in [[Ann Arbor, Michigan]] serving Michigan, formed in 1966,<ref name="Merit1998PartOne">{{cite web|last=Aupperle|first=Eric M.|year=1998|title=Merit–Who, What, and Why, Part One: The Early Years, 1964-1983|url=http://www.merit.edu/about/history/pdf/MeritHistory.pdf|url-status=live|archive-url=https://web.archive.org/web/20130423042006/http://merit.edu/about/history/pdf/MeritHistory.pdf|archive-date=2013-04-23|website=Merit Network, Inc., in Library Hi Tech|volume=16|issue=1}}</ref> still in operation {{as of|2023|lc=on}};<ref>{{cite web |url=https://www.merit.edu/network/internet/ |title=Merit Internet |access-date=2023-06-05}}</ref>
*[[MIDnet]] in [[Lincoln, Nebraska]] serving Arkansas, Iowa, Kansas, Missouri, Nebraska, Oklahoma, and South Dakota;
*[[NEARNET]], the New England Academic and Research Network in [[Cambridge, Massachusetts]], added as part of the upgrade to T3, serving Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont, established in late 1988, operated by [[BBN Technologies|BBN]] under contract to MIT, BBN assumed responsibility for NEARNET on 1 July 1993;<ref>{{cite web|url=http://web.mit.edu/newsoffice/1993/bbn-0714.html|title=BBN to operate NEARnet|website=MIT News|date=14 July 1993}}</ref>
*NorthWestNet in [[Seattle, Washington]], serving Alaska, Idaho, Montana, North Dakota, Oregon, and Washington, founded in 1987;<ref>{{cite web|url=http://www.gutenberg.org/files/40/40-ps.ps|title=About NorthWestNet|website=NorthWestNet User Services Internet Resource Guide, NorthWestNet Academic Computing Consortium, Inc.|date=24 March 1992|access-date=3 July 2012}}</ref>
*[[NYSERNet]], New York State Education and Research Network in [[Ithaca, New York]];
*JVNCNet, the John von Neumann National Supercomputer Center Network in [[Princeton, New Jersey]], serving Delaware and New Jersey;
*SESQUINET, the Sesquicentennial Network in [[Houston, Texas]], founded during the 150th anniversary of the State of [[Texas]];
*[[SURAnet]], the Southeastern Universities Research Association network in [[College Park, Maryland]] and later as part of the T3 upgrade in [[Atlanta, Georgia]] serving Alabama, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia, sold to [[BBN Technologies|BBN]] in 1994; and
*Westnet in [[Salt Lake City, Utah]] and [[Boulder, Colorado]], serving Arizona, Colorado, New Mexico, Utah, and Wyoming.

====National LambdaRail====
The [[National LambdaRail]] (NRL) was launched in September 2003. It is a 12,000-mile high-speed national computer network owned and operated by the US research and education community that runs over fiber-optic lines. It was the first transcontinental [[10 Gigabit Ethernet]] network. It operates with an aggregate capacity of up to {{nowrap|1.6 Tbit/s}} and a {{nowrap|40 Gbit/s}} bitrate.<ref>{{Cite news |title= National LambdaRail Opens for Business |author= Michael Feldman |work= HPCwire |date= October 28, 2008 |url= http://www.hpcwire.com/hpcwire/2008-10-28/national_lambdarail_opens_for_business.html |access-date= June 6, 2013}}</ref><ref>{{cite web|url=http://www.nlr.net/about.php|title=About NLR|archive-url=https://archive.today/20130904020736/http://www.nlr.net/about.php |archive-date=2013-09-04|website=National LambdaRail|date=3 September 2013}}</ref> NLR ceased operations in March 2014.

==== TransPAC2, and TransPAC3====
[[TransPAC2]]  is a high-speed international Internet service connecting research and education networks in the Asia-Pacific region to those in the US.<ref>{{cite web|url=http://www.hpcwire.com/hpcwire/2005-04-08/international_transpac2_inaugurated-1.html|title=International TransPAC2 Inaugurated|archive-url=https://archive.today/20130620034322/http://www.hpcwire.com/hpcwire/2005-04-08/international_transpac2_inaugurated-1.html |archive-date=20 June 2013}}, ''HPC Wire'', 8 April 2005.</ref> TransPAC3 is part of the NSF's International Research Network Connections (IRNC) program.<ref>{{cite web|url=http://www.irnclinks.net/#transpac3|title=TransPAC3 - Asia-US High Performance International Networking|work=International Research Network Connections Program (IRNC), U.S. National Science Foundation, October 2011.|access-date=3 September 2013|archive-date=14 August 2013|archive-url=https://web.archive.org/web/20130814194934/http://irnclinks.net/#transpac3|url-status=dead}}</ref>

====Very high-speed Backbone Network Service (vBNS)====
The [[Very high-speed Backbone Network Service]] (vBNS) came on line in April 1995 as part of a NSF sponsored project to provide high-speed interconnection between NSF-sponsored [[supercomputing]] centers and select access points in the United States.<ref>{{cite web|url=http://w2.eff.org/Infrastructure/Govt_docs/nsf_nren.rfp|title=NSF Solicitation 93-52-Network Access Point Manager, Routing Arbiter, Regional Network Providers, and Very High Speed Backbone Network Services Provider for NSFNET and the NREN(SM) Program|archive-url=https://web.archive.org/web/20160305030153/https://w2.eff.org/Infrastructure/Govt_docs/nsf_nren.rfp|archive-date=2016-03-05|date=May 6, 1993}}</ref> The network was engineered and operated by [[MCI Telecommunications]] under a cooperative agreement with the NSF. By 1998, the vBNS had grown to connect more than 100 universities and research and engineering institutions via 12 national points of presence with [[DS-3]] ({{nowrap|45 Mbit/s}}), [[OC-3c]] ({{nowrap|155 Mbit/s}}), and [[OC-12]] ({{nowrap|622 Mbit/s}}) links on an all OC-12 backbone, a substantial engineering feat for that time. The vBNS installed one of the first ever production [[OC-48]] ({{nowrap|2.5 Gbit/s}}) IP links in February 1999 and went on to upgrade the entire backbone to OC-48.<ref>{{cite journal |title=vBNS: not your father's Internet |first1=John |last1=Jamison |first2=Randy |last2=Nicklas |first3=Greg |last3=Miller |first4=Kevin |last4=Thompson |first5=Rick |last5=Wilder |first6=Laura |last6=Cunningham |first7=Chuck |last7=Song |journal=IEEE Spectrum |volume=35 |issue=7 |date=July 1998 |pages=38–46 |doi=10.1109/6.694354}}</ref>

In June 1999 MCI WorldCom introduced vBNS+ which allowed attachments to the vBNS network by organizations that were not approved by or receiving support from NSF.<ref>{{cite web|url=http://www.verizonbusiness.com/about/news/pr-5449-en-MCI+WorldCom+Introduces+Next+Generation+vBNS%2B+For+All+Higher+Education+And+Research+Organizations.xml|title=MCI WorldCom Introduces Next Generation vBNS+ For All Higher Education And Research Organizations|website=Verizon Business News|date=June 23, 1999}}</ref> After the expiration of the NSF agreement, the vBNS largely transitioned to providing service to the government. Most universities and research centers migrated to the Internet2 educational backbone. In January 2006, when [[MCI Inc.|MCI]] and [[Verizon]] merged,<ref>{{cite web|url=http://www.verizonbusiness.com/about/news/pr-18593-en-Verizon+and+MCI+Close+Merger,+Creating+a+Stronger+Competitor+for+Advanced+Communications+Services.xml|title=Verizon and MCI Close Merger, Creating a Stronger Competitor for Advanced Communications Services|website=Verizon Business News|date=January 6, 2006}}</ref> vBNS+ became a service of [[Verizon Business]].<ref>{{cite web|url=http://www.verizonbusiness.com/solutions/government/federal/contracts/fts2001_bridge/rg_products/vbns/|title=vBNS+|website=Verizon Business}}</ref>

==See also==
*[[Multi-bearer network]]
*[[Optical burst switching]]
*[[Packet radio]]
*[[Transmission delay]]
*[[Virtual private network]]

==References==
{{Reflist}}

===Bibliography===
*{{Cite book |last=Abbate |first=Janet |title=Inventing the Internet |publisher=MIT Press |year=2000 |isbn=9780262511155 |url-access=registration |url=https://archive.org/details/inventinginterne00jane}}
*{{cite book |last1=Gillies |first1=James |title=How the Web was born : the story of the World Wide Web |last2=Cailliau |first2=Robert |date=2000 |publisher=Oxford University Press |isbn=0-19-286207-3 |publication-place=Oxford |oclc=43377073}}
* {{cite book |last=Hafner |first=Katie |title=Where Wizards Stay Up Late |publisher=Simon and Schuster |date=1996 |pages=52–67 |url=https://books.google.com/books?id=8TEjhArXaBsC&q=editions:jQP_fBq3Mr4C |isbn=9780684832678}}
* {{cite book |last1=Norberg |first1=Arthur |last2=O'Neill |first2=Judy E. |title=Transforming Computer Technology: Information Processing for the Pentagon, 1962-1982 |publisher=Johns Hopkins University |date=2000 |isbn=978-0801863691}}
* {{Cite book |last=Moschovitis |first=Christos J. P. |url=https://archive.org/details/historyofinterne0000unse |title=History of the Internet: A Chronology, 1843 to the Present |date=1999 |publisher=ABC-CLIO |isbn=978-1-57607-118-2}}
* Lawrence Roberts, ''[https://web.archive.org/web/20160324033133/http://www.packet.cc/files/ev-packet-sw.html The Evolution of Packet Switching]'' (Proceedings of the IEEE, November, 1978)

=== Primary sources ===
*Paul Baran et al., ''[http://www.rand.org/about/history/baran-list.html On Distributed Communications, Volumes I-XI] {{Webarchive|url=https://web.archive.org/web/20110329223245/http://www.rand.org/about/history/baran-list.html |date=2011-03-29 }}'' (RAND Corporation Research Documents, August, 1964)
*Paul Baran, ''[http://www.rand.org/publications/RM/RM3420/ On Distributed Communications: I Introduction to Distributed Communications Network]'' (RAND Memorandum RM-3420-PR. August 1964)
*Paul Baran, [http://www.cs.ucla.edu/classes/cs217/Baran64.pdf On Distributed Communications Networks], ([[IEEE]] Transactions on Communications Systems, Vol. CS-12 No. 1, pp.&nbsp;1–9, March 1964)
*D. W. Davies, K. A. Bartlett, R. A. Scantlebury, and P. T. Wilkinson, ''[[doi:10.1145/800001.811669|A digital communications network for computers giving rapid response at remote terminals]]'' (ACM Symposium on Operating Systems Principles. October 1967)
*R. A. Scantlebury, P. T. Wilkinson, and K. A. Bartlett, ''[https://researchr.org/publication/ScantleburyWB68 The design of a message switching Centre for a digital communication network]'' (IFIP 1968)

==Further reading==
*{{cite book |last1=Pelkey |first1=James L. |title=Circuits, Packets, and Protocols: Entrepreneurs and Computer Communications, 1968-1988 |last2=Russell |first2=Andrew L. |last3=Robbins |first3=Loring G. |date=2022 |publisher=Morgan & Claypool |isbn=978-1-4503-9729-2}}
* {{cite book |last1=Russell |first1=Andrew L. |title=Open Standards and the Digital Age: History, Ideology, and Networks |date=2014 |publisher=Cambridge University Press |isbn=978-1-139-91661-5}}

==External links==
*{{Citation | last = Wilkinson | first = Peter | title = Packet Switching and the NPL Network | journal = Computer Resurrection: The Journal of the Computer Conservation Society | issue = 90 | date = Summer 2020 | url = https://www.computerconservationsociety.org/resurrection/res90.htm#c | issn = 0958-7403 }}
*[http://purl.umn.edu/107101 Oral history interview with Paul Baran]. [[Charles Babbage Institute]] University of Minnesota, Minneapolis. Baran describes his working environment at RAND, as well as his initial interest in survivable communications, and the evolution, writing and distribution of his eleven-volume work, "On Distributed Communications". Baran discusses his interaction with the group at ARPA who were responsible for the later development of the ARPANET.
*[https://www.youtube.com/watch?v=L_ojeeTIqFM&index=29&list=PL59D1CD3E3C7C070F NPL Data Communications Network] NPL video, 1970s
*[http://www.livinginternet.com/i/iw_packet.htm Packet Switching History and Design], site reviewed by Baran, Roberts, and Kleinrock
*[http://www.rand.org/about/history/baran.html Paul Baran and the Origins of the Internet]
*{{Citation |url=http://www.rogerdmoore.ca/PS |title=20+ articles on packet switching in the 1970s |archive-url=https://web.archive.org/web/20090801003519/http://www.rogerdmoore.ca/PS/ |archive-date=2009-08-01}}
*{{cite magazine |url=http://www.phrack.org/issues.html?issue=18&id=3#article |title=An Introduction to Packet Switched Networks |magazine=[[Phrack]] |date=May 3, 1988 |archive-url=https://web.archive.org/web/20231204132134/http://phrack.org/issues/18/3.html |archive-date=2023-12-04 |url-status=live}}

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[[Category:Computer networking]]
[[Category:History of the Internet]]
[[Category:Network protocols]]
[[Category:Packets (information technology)| ]]