View source for ARPANET

{{Short description|Early packet switching network (1969–1990)}}
{{for-multi|the episode of the television series The Americans|Arpanet (The Americans)}}
{{Use American English|date=October 2020}}
{{Use dmy dates|date=February 2020}}

{{Infobox telecommunications network
| name =
| logo =
| image = [[File:Arpanet logical map, march 1977.png|300px]]
| caption = ARPANET logical map, March 1977
| commercial = No
| type = Data<!-- data | voice | mobile | data and voice -->
| location = [[United States]], [[United Kingdom]], [[Norway]]
| operator = From 1975, [[Defense Communications Agency]]
| protocols = [[OSI model#Layer architecture|Layers]] 1-3: [[1822 protocol]] (IMP-host), internal/undocumented (IMP-IMP) <br /> Layers 4+: [[Network Control Protocol (ARPANET)|NCP]], later [[TCP/IP]]
| established = {{start date and age|1969}}
| closed = {{start date and age|1990}}
| funding = From 1966, [[Advanced Research Projects Agency]] (ARPA)
| website =<!-- {{URL}} -->
}}
[[File:Arpanet in the 1970s.png|thumb|upright=1.35|ARPANET access points in the 1970s]]
{{Internet history timeline}}

The '''Advanced Research Projects Agency Network''' ('''ARPANET''') was the first wide-area [[packet-switched network]] with distributed control and one of the first computer networks to implement the [[TCP/IP]] protocol suite. Both technologies became the technical foundation of the [[Internet]]. The ARPANET was established by the [[Advanced Research Projects Agency]] (now DARPA) of the [[United States Department of Defense]].<ref name="LIARPANETTheFirstInternet">{{Cite web|title=ARPANET – The First Internet|url=https://www.livinginternet.com/internet/i/ii_arpanet.htm|website=Living Internet|access-date=2021-03-19}}</ref>

Building on the ideas of [[J. C. R. Licklider]], [[Robert Taylor (computer scientist)|Bob Taylor]] initiated the ARPANET project in 1966 to enable [[resource sharing]] between remote computers.<ref>{{Cite news |title=An Internet Pioneer Ponders the Next Revolution|date=December 20, 1999|work=The New York Times|url= https://archive.nytimes.com/www.nytimes.com/library/tech/99/12/biztech/articles/122099outlook-bobb.html |access-date=2020-02-20|quote=Mr. Taylor wrote a white paper in 1968, a year before the network was created, with another ARPA research director, J. C. R. Licklider. The paper, "The Computer as a Communications Device," was one of the first clear statements about the potential of a computer network.}}</ref> Taylor appointed [[Lawrence Roberts (scientist)|Larry Roberts]] as program manager. Roberts made the key decisions about the [[request for proposal]] to build the network.<ref>{{Cite news|last=Hafner |first=Katie |date=2018-12-30 |title=Lawrence Roberts, Who Helped Design Internet's Precursor, Dies at 81|work=The New York Times |url=https://www.nytimes.com/2018/12/30/obituaries/lawrence-g-roberts-dies-at-81.html|access-date=2020-02-20|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> He incorporated [[Donald Davies]]' concepts and designs for packet switching,<ref>{{Cite web |url=https://history.computer.org/pioneers/davies.html|title=Computer Pioneers - Donald W. Davies|website=IEEE Computer Society|access-date=2020-02-20|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>{{Cite news |url=https://www.washingtonpost.com/sf/business/2015/05/30/net-of-insecurity-part-1/|title=A Flaw In The Design|date=May 30, 2015 |newspaper= The Washington Post|quote=The Internet was born of a big idea: Messages could be chopped into chunks, sent through a network in a series of transmissions, then reassembled by destination computers quickly and efficiently. Historians credit seminal insights to Welsh scientist Donald W. Davies and American engineer Paul Baran. ... The most important institutional force ... was the Pentagon's Advanced Research Projects Agency (ARPA) ... as ARPA began work on a groundbreaking computer network, the agency recruited scientists affiliated with the nation's top universities.}}</ref> and sought input from [[Paul Baran]] on dynamic routing.<ref name="Abbate20003">{{cite book|last1=Abbate|first1=Janet|year=2000 |url=https://books.google.com/books?id=9BfZxFZpElwC&pg=PA37 |title=Inventing the Internet|publisher=[[MIT Press]]|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> In 1969, ARPA awarded the contract to build the [[Interface Message Processor]]s (IMPs) for the network to [[Bolt Beranek & Newman]] (BBN).<ref>{{Cite web |title=A Brief History of the Internet |url=https://www.internetsociety.org/internet/history-internet/brief-history-internet/ |access-date=2024-05-25 |website=Internet Society |language=en-US}}</ref><ref>{{Cite web |title=ARPANET |url=https://www.darpa.mil/about-us/timeline/arpanet |access-date=May 25, 2024 |website=darpa.mil}}</ref> The design was led by [[Bob Kahn]] who developed the first [[Communication protocol|protocol]] for the network. Roberts engaged [[Leonard Kleinrock]] at [[UCLA]] to develop mathematical methods for analyzing the packet network technology.<ref name="Abbate20003" />

The first computers were connected in 1969 and the [[Network Control Protocol (ARPANET)|Network Control Protocol]] was implemented in 1970, development of which was led by [[Steve Crocker]] at UCLA and other graduate students, including [[Jon Postel]] and others.{{Ref RFC|6529}}<ref name=":6">{{Cite book|last=Bidgoli|first=Hossein|url=https://books.google.com/books?id=gZ9srwU_9xMC&q=ARPANET&pg=PA118|title=The Internet Encyclopedia, Volume 2 (G - O)|date=2004-05-11|publisher=John Wiley & Sons|isbn=978-0-471-68996-6|pages=39|language=en}}</ref><ref name=":4">{{cite book|first1=K. G.|last1=Coffman|first2=A. M.|last2=Odlyzco|chapter-url=https://books.google.com/books?id=TXhWJcsO134C&q=ARPANET&pg=PA29|title=Optical Fiber Telecommunications IV-B: Systems and Impairments|publisher=[[Academic Press]]|date=2002|chapter=Growth of the Internet|isbn=978-0123951731|editor1-first=I.|editor1-last=Kaminow|editor2-first=T.|editor2-last=Li|access-date=15 August 2015}}</ref> The network was declared operational in 1971. Further software development enabled [[remote login]] and [[file transfer]], which was used to provide an early form of [[email]].<ref name=":5">{{cite book|first=L. A.|last=Lievrouw|url=https://books.google.com/books?id=NZ3ktyGA0rwC&q=ARPANET&pg=PA253|title=Handbook of New Media: Student Edition|page=253|editor1-first=L. A.|editor1-last=Lievrouw|editor2-first=S. M.|editor2-last=Livingstone|publisher=[[SAGE Publications|SAGE]]|date=2006|isbn=1412918731|access-date=15 August 2015}}</ref> The network expanded rapidly and operational control passed to the [[Defense Information Systems Agency#Defense Communications Agency|Defense Communications Agency]] in 1975.

Bob Kahn moved to DARPA and, together with [[Vint Cerf]] at [[Stanford University]], formulated the [[Transmission Control Program]] for [[internetworking]].<ref name=":1">{{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|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> As this work progressed, a protocol was developed by which multiple separate networks could be joined into a network of networks; this incorporated concepts pioneered in the French [[CYCLADES]] project directed by [[Louis Pouzin]]. Version 4 of [[TCP/IP]] was installed in the ARPANET for production use in January 1983 after the Department of Defense made it standard for all military computer networking.<ref name="R. Oppliger">{{cite book|author=R. Oppliger|url=https://books.google.com/books?id=vtyowiyW9BkC&q=ARPANET&pg=PA12|title=Internet and Intranet Security|date=2001|publisher=Artech House|isbn=978-1-58053-166-5|page=12|access-date=15 August 2015}}</ref><ref name="LITCPIP">{{Cite web|url=https://www.livinginternet.com/internet/i/ii_tcpip.htm|title=TCP/IP Internet Protocol|website=Living Internet|access-date=2021-03-19}}</ref>

Access to the ARPANET was expanded in 1981 when the [[National Science Foundation]] (NSF) funded the [[Computer Science Network]] (CSNET). In the early 1980s, the NSF funded the establishment of national supercomputing centers at several universities and provided network access and network interconnectivity with the [[NSFNET]] project in 1986. The ARPANET was formally decommissioned in 1990, after [[Internet protocol suite#Adoption|partnerships with the telecommunication and computer industry]] had assured private sector expansion and commercialization of an expanded worldwide network, known as the Internet.<ref>{{cite book |last1=Fidler |first1=Bradley |last2=Mundy |first2=Russ |title=The Creation and Administration of Unique Identifiers, 1967-2017 |date=November 2020 |publisher=ICANN |chapter=1.2 |page=8 |url=https://www.icann.org/en/system/files/files/creation-administration-unique-identifiers-1967-2017-18nov20-en.pdf |access-date=14 May 2021}}</ref>

== History ==
=== Inspiration ===
Historically, voice and data communications were based on methods of [[circuit switching]], as exemplified in the traditional telephone network, wherein each telephone call is allocated a dedicated end-to-end electronic connection between the two communicating stations. The connection is established by switching systems that connected multiple intermediate call legs between these systems for the duration of the call.

The traditional model of the circuit-switched telecommunication network was challenged in the early 1960s by [[Paul Baran]] at the [[RAND Corporation]], who had been researching systems that could sustain operation during partial destruction, such as by nuclear war. He developed the theoretical model of ''distributed adaptive message block switching''.<ref name="RAND corporation">{{cite web|url=https://www.rand.org/about/history/baran.list.html |title=Paul Baran and the Origins of the Internet |publisher=RAND corporation |access-date=29 March 2011}}</ref> However, the telecommunication establishment rejected the development in favor of existing models. [[Donald Davies]] at the United Kingdom's [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL) independently arrived at a similar concept in 1965.<ref>{{cite web|last=Scantlebury|first=Roger|title=''Internet pioneers airbrushed from history''|url=https://www.theguardian.com/technology/2013/jun/25/internet-pioneers-airbrushed-from-history|date=25 June 2013|work=The Guardian|access-date=1 August 2015}}</ref><ref>{{cite web|title=''Packets of data were the key...''|url=http://www.npl.co.uk/news/packets-of-data|publisher=NPL|access-date=1 August 2015}}</ref>

The earliest ideas for a [[computer network]] intended to allow general communications among computer users were formulated by [[computer scientist]] [[J. C. R. Licklider]] of [[Bolt Beranek and Newman]] (BBN), in April 1963, in memoranda discussing the concept of the "[[Intergalactic Computer Network]]". Those ideas encompassed many of the features of the contemporary Internet. In October 1963, Licklider was appointed head of the Behavioral Sciences and Command and Control programs at the Defense Department's [[Advanced Research Projects Agency]] (ARPA). He convinced [[Ivan Sutherland]] and [[Robert Taylor (computer scientist)|Bob Taylor]] that this network concept was very important and merited development, although Licklider left ARPA before any contracts were assigned for development.<ref>{{cite web|url=http://www.livinginternet.com/internet/i/ii_licklider.htm|title=J.C.R. Licklider And The Universal Network|website=Living Internet|access-date=2021-03-19}}</ref>

Sutherland and Taylor continued their interest in creating the network, in part, to allow ARPA-sponsored researchers at various corporate and academic locales to utilize computers provided by ARPA, and, in part, to quickly distribute new software and other [[computer science]] results.<ref>{{cite web|url=http://www.livinginternet.com/internet/i/ii_ipto.htm|title=IPTO – Information Processing Techniques Office|website=Living Internet|access-date=2021-03-19}}</ref> Taylor had three computer terminals in his office, each connected to separate computers, which ARPA was funding: one for the [[System Development Corporation]] (SDC) [[AN/FSQ-32|Q-32]] in [[Santa Monica]], one for [[Project Genie]] at the [[University of California, Berkeley]], and another for [[Multics]] at the [[Massachusetts Institute of Technology]]. Taylor recalls the circumstance: "For each of these three terminals, I had three different sets of user commands. So, if I was talking online with someone at S.D.C., and I wanted to talk to someone I knew at Berkeley, or M.I.T., about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. I said, 'Oh Man!', it's obvious what to do: If you have these three terminals, there ought to be one terminal that goes anywhere you want to go. That idea is the ARPANET".<ref>{{cite news |title=An Internet Pioneer Ponders the Next Revolution |first=John |last=Markoff |url=http://partners.nytimes.com/library/tech/99/12/biztech/articles/122099outlook-bobb.html |work=The New York Times |access-date=20 September 2008 | date=20 December 1999| archive-url= https://web.archive.org/web/20080922095019/http://partners.nytimes.com/library/tech/99/12/biztech/articles/122099outlook-bobb.html| archive-date= 22 September 2008 | url-status= live}}</ref>

Donald Davies' work caught the attention of ARPANET developers at [[Symposium on Operating Systems Principles]] in October 1967.<ref name="Isaacson2014"/> He gave the first public presentation, having coined the term ''[[packet switching]]'', in August 1968 and incorporated it into the [[NPL network]] in England.<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}}</ref><ref>{{cite news|title=The accelerator of the modern age |date=5 August 2008 |url=http://news.bbc.co.uk/1/hi/technology/7541123.stm|work=BBC News|access-date=19 May 2009}}</ref> The NPL network and ARPANET were the first two networks in the world to implement packet switching.<ref name="Roberts1978">{{cite web|last1=Roberts|first1=Lawrence G.|date=November 1978|title=The Evolution of Packet Switching |url=http://www.packet.cc/files/ev-packet-sw.html|access-date=9 April 2016|archive-date=24 March 2016 |archive-url=https://web.archive.org/web/20160324033133/http://www.packet.cc/files/ev-packet-sw.html|url-status=dead}}</ref><ref name="C. Hempstead, W. Worthington">{{cite book |author1=C. Hempstead |url=https://books.google.com/books?id=2ZCNAgAAQBAJ&q=NPL%20Network&pg=PA574 |title=Encyclopedia of 20th-Century Technology |author2=W. Worthington |date=8 August 2005 |publisher=[[Routledge]] 8 August 2005, 992 pages, (edited by C. Hempstead, W. Worthington) |isbn=978-1-135-45551-4 |access-date=15 August 2015}}</ref><ref name="Davies">{{cite web |title=Donald Davies |url=http://www.internethalloffame.org/inductees/donald-davies |website=internethalloffame.org}}</ref> Roberts said the computer networks built in the 1970s were similar "in nearly all respects" to Davies' original 1965 design.<ref name=":2">{{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|journal=IEEE Invited Paper|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.|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|url-status=dead}}</ref>

=== Creation ===
In February 1966, Bob Taylor successfully lobbied ARPA's Director [[Charles M. Herzfeld]] to fund a network project. Herzfeld redirected funds in the amount of one million dollars from a ballistic missile defense program to Taylor's budget.<ref>Markoff, John, Innovator who helped create PC, Internet and the mouse, New York Times, 15 April 2017, p.A1</ref> Taylor hired [[Lawrence Roberts (scientist)|Larry Roberts]] as a program manager in the ARPA [[Information Processing Techniques Office]] in January 1967 to work on the ARPANET.<ref name=":24">{{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 met Paul 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>

Roberts 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=":24" /> In April 1967, ARPA held a design session on technical standards. The initial standards for identification and authentication of users, transmission of characters, and error checking and retransmission procedures were discussed.<ref>{{cite web|url=https://www.livinginternet.com/internet/i/ii_roberts.htm|title=Lawrence Roberts Manages The ARPANET Program|date=7 January 2000|website=Living Internet|access-date=2021-03-19}}</ref> Roberts' proposal was that all mainframe computers would connect to one another directly. The other investigators were reluctant to dedicate these computing resources to network administration. After the design session, [[Wesley A. Clark|Wesley Clark]] proposed minicomputers should be used as an interface to create a [[message switching]] network. Roberts modified the ARPANET plan to incorporate Clark's suggestion and named the minicomputers [[Interface Message Processor]]s (IMPs).<ref name=":24" /><ref>{{Cite web |url=https://www.forbes.com/sites/gilpress/2015/01/02/a-very-short-history-of-the-internet-and-the-web-2/|title=A Very Short History Of The Internet And The Web|last=Press|first=Gil|website=Forbes|access-date=2020-02-07}}</ref><ref>{{Cite web|url=https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/EngelbartPapers/B1_F20_CompuMtg.html|title=SRI Project 5890-1; Networking (Reports on Meetings).[1967]|website=web.stanford.edu|access-date=2020-02-15|quote=W. Clark's message switching proposal (appended to Taylor's letter of April 24, 1967 to Engelbart) were reviewed.|archive-date=2 February 2020|archive-url=https://web.archive.org/web/20200202062940/https://web.stanford.edu/dept/SUL/library/extra4/sloan/mousesite/EngelbartPapers/B1_F20_CompuMtg.html|url-status=dead}}</ref><ref name="LivingInternetIMP">{{cite web|url=https://www.livinginternet.com/internet/i/ii_imp.htm |title=IMP – Interface Message Processor|date=7 January 2000|website=Living Internet|access-date=2021-03-19}}</ref>

The plan was presented at the inaugural Symposium on Operating Systems Principles in October 1967.<ref>{{Cite book|last=Roberts|first=Lawrence|date=1967|title=Multiple Computer Networks and Intercomputer Communications|chapter=Multiple computer networks and intercomputer communication|chapter-url=https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/arpanet.pdf|pages=3.1–3.6|doi=10.1145/800001.811680|s2cid=17409102|quote=Thus the set of IMP's, plus the telephone lines and data sets would constitute a message switching network}}</ref> Donald Davies' work on packet switching and the NPL network, presented by a colleague ([[Roger Scantlebury]]), and that of Paul Baran, came to the attention of the ARPA investigators at this conference.<ref name="Gillies2000">{{cite book|last1=Gillies|first1=James|last2=Cailliau|first2=Robert|title=How the Web was Born: The Story of the World Wide Web|date=2000|publisher=Oxford University Press|isbn=978-0-19-286207-5|page=25|url=https://books.google.com/books?id=pIH-JijUNS0C&pg=PA25}}</ref><ref name="Isaacson2014">{{cite book|last1=Isaacson|first1=Walter|title=The Innovators: How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution|date=2014|publisher=Simon & Schuster|isbn=978-1-4767-0869-0|page=237|url=https://books.google.com/books?id=4V9koAEACAAJ&pg=PA237}}</ref> Roberts applied Davies' concept of packet switching for the ARPANET,<ref>{{cite web|title=Inductee Details – Donald Watts Davies|url=http://www.invent.org/honor/inductees/inductee-detail/?IID=328|publisher=National Inventors Hall of Fame|access-date=6 September 2017|archive-url=https://web.archive.org/web/20170906091936/http://www.invent.org/honor/inductees/inductee-detail/?IID=328|archive-date=6 September 2017|url-status=dead}}</ref><ref name="MCK">{{cite journal|first=Martin|last=Cambell-Kelly |title=Pioneer Profiles: Donald Davies|journal=Computer Resurrection|number=44|date=Autumn 2008|issn=0958-7403|url=http://www.computerconservationsociety.org/resurrection/res44.htm}}</ref> and sought input from Paul Baran on dynamic routing.<ref name="Abbate20002">{{cite book|last1=Abbate|first1=Janet|author-link=Janet Abbate|url=https://books.google.com/books?id=9BfZxFZpElwC&pg=PA37|title=Inventing the Internet|date=2000|publisher=[[MIT Press]]|isbn=978-0-2625-1115-5 |location=Cambridge, MA|pages=37–38, 58–59}}</ref> The NPL network was using line speeds of 768&nbsp;kbit/s, and the proposed line speed for the ARPANET was upgraded from 2.4&nbsp;kbit/s to 50&nbsp;kbit/s.<ref name="brief">{{cite web|title=Brief History of the Internet|url=http://www.internetsociety.org/internet/what-internet/history-internet/brief-history-internet#f5|publisher=Internet Society|access-date=12 July 2017}}</ref>

By mid-1968, Roberts and Barry Wessler wrote a final version of the IMP specification based on a [[Stanford Research Institute]] (SRI) report that ARPA commissioned to write detailed specifications describing the ARPANET communications network.<ref name="LivingInternetIMP"/> Roberts gave a report to Taylor on 3 June, who approved it on 21 June. After approval by ARPA, a [[Request for Quotation]] (RFQ) was issued for 140 potential bidders. Most computer science companies regarded the ARPA proposal as outlandish, and only twelve submitted bids to build a network; of the twelve, ARPA regarded only four as top-rank contractors. At year's end, ARPA considered only two contractors and awarded the contract to build the network to BBN in January 1969.<ref name="Roberts1978"/>
[[File:1969 ARPANET BBN IMP.jpg|thumb|1969 ARPANET IMP]]
The initial, seven-person BBN team were much aided by the technical specificity of their response to the ARPA RFQ, and thus quickly produced the first working system. The "IMP guys" were led by [[Frank Heart]]; the theoretical design of the network was led by [[Bob Kahn]]; the team included [[David Walden|Dave Walden]], [[Severo Ornstein]], [[William Crowther (programmer)|William Crowther]] and several others.<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=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>{{Cite news|last=Hafner|first=Katie|url=https://www.nytimes.com/2018/06/25/technology/frank-heart-who-linked-computers-before-the-internet-dies-at-89.html|title=Frank Heart, Who Linked Computers Before the Internet, Dies at 89|date=2018-06-25|work=The New York Times|access-date=2020-04-03|language=en-US|issn=0362-4331}}</ref><ref name="Hafner1">{{harvnb|Hafner|Lyon|1996|pp=[https://archive.org/details/wherewizardsstay00haf_vgj/page/116/mode/2up?q=kahn 116, 149]}}</ref> The BBN-proposed network closely followed Roberts' ARPA plan: a network composed of small computers, the IMPs (similar to the later concept of [[Router (computing)|routers]]), that functioned as gateways interconnecting local resources. Routing, flow control, software design and network control were developed by the BBN team.<ref name=":23" /><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> At each site, the IMPs performed store-and-forward packet switching functions and were interconnected with [[leased line]]s via telecommunication data sets ([[modem]]s), with initial data rates of {{gaps|50|[[kilobit|kbit]]/s}}.<ref name="brief" /><ref>{{cite book |url=https://archive.org/details/DTIC_ADA096798 |title=ARPANET Information Brochure |date=May 1980 |page=12 |quote=The complete network is formed by interconnecting the nodes through wideband communication lines, normally 50,000 bits per second (50KBPS), supplied by common carriers}}</ref><ref>{{cite report | title=BBN Report No. 1928| date=January 1970| url=http://bärwolff.de/bbn-arpanet-reports-collection/BBN%20(1970)%20Interface%20Message%20Processors%20for%20the%20ARPA%20Computer%20Network%20(Report%201928,%20Quarterly%20Technical%20Report%204).pdf| quote=we designed and implemented a test program to obtain data on the performance of the fifty kilobit communication circuits}}</ref> The host computers were connected to the IMPs via custom [[serial communication]] interfaces. The system, including the hardware and the packet switching software, was designed and installed in nine months.<ref name="Roberts1978"/><ref name="LivingInternetIMP"/><ref>{{cite web|title=Looking back at the ARPANET effort, 34 years later|url=https://www.livinginternet.com/internet/i/ii_imp_walden.htm|access-date=2021-03-19|date=February 2003}}</ref> The BBN team continued to interact with the NPL team with meetings between them taking place in the U.S. and the U.K.<ref name="Abbate2000">{{cite book|last1=Abbate|first1=Janet|title=Inventing the Internet|date=2000|location=Cambridge, MA|publisher=[[MIT Press]]|isbn=978-0-2625-1115-5|page=38|url=https://books.google.com/books?id=9BfZxFZpElwC&pg=PA38}}</ref><ref>{{cite conference |first1=Frank |last1=Heart |author-link2=Bob Kahn |first2=Robert |last2=Kahn |first3=Severo |last3=Ornstein |author-link3=Severo Ornstein |first4=William |last4=Crowther |author-link4=William Crowther (programmer) |first5=David |last5=Walden |title=Proceedings of the May 5-7, 1970, spring joint computer conference on - AFIPS '70 (Spring) |chapter=The Interface Message Processor for the ARPA Computer Network |chapter-url=http://www.walden-family.com/public/1970-imp-afips.pdf |conference=1970 Spring Joint Computer Conference |page=565 |year=1970 |doi=10.1145/1476936.1477021|s2cid=9647377 }}</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}}</ref>

As with the NPL network, the first-generation IMPs were built by BBN using a [[rugged computer]] version of the [[Honeywell]] [[DDP-516]] computer, configured with {{gaps|24|[[kibibyte|KB]]}} of expandable [[magnetic-core memory]], and a 16-channel Direct Multiplex Control (DMC) [[direct memory access]] unit.<ref>{{cite web|last=Wise|first=Adrian|url=https://www.old-computers.com/museum/computer.asp?c=551|title=Honeywell DDP-516|website=Old-Computers.com|access-date=6 June 2020|archive-url=https://web.archive.org/web/20200726104820/https://www.old-computers.com/museum/computer.asp?c=551|archive-date=26 July 2020|url-status=dead}}</ref> The DMC established custom interfaces with each of the host computers and modems. In addition to the front-panel lamps, the DDP-516 computer also features a special set of 24 indicator lamps showing the status of the IMP communication channels. Each IMP could support up to four local hosts and could communicate with up to six remote IMPs via early [[Digital Signal 0]] leased telephone lines. The network connected one computer in Utah with three in California. Later, the Department of Defense allowed the universities to join the network for sharing hardware and software resources.

==== Debate about design goals ====

According to Charles Herzfeld, ARPA Director (1965–1967):{{blockquote|The ARPANET was not started to create a Command and Control System that would survive a nuclear attack, as many now claim. To build such a system was, clearly, a major military need, but it was not ARPA's mission to do this; in fact, we would have been severely criticized had we tried. Rather, the ARPANET came out of our frustration that there were only a limited number of large, powerful research computers in the country, and that many research investigators, who should have access to them, were geographically separated from them.<ref>{{cite web|title=50 years ago today, the Internet was born. Sort of |website=[[ArsTechnica.com]] |date=29 October 2019 |url=https://arstechnica.com/information-technology/2019/10/50-years-ago-today-the-internet-was-born-sort-of/ |access-date=2022-06-21}}</ref>}}

The ARPANET used distributed computation and incorporated frequent re-computation of routing tables (automatic routing was technically challenging at the time). These features increased the survivability of the network in the event of significant interruption. Furthermore, the ARPANET was designed to survive subordinate network losses.<ref>{{cite book |first=Janet|last=Abbate|date=2000|title=Inventing the Internet|pages=194–195|location=Cambridge, MA|publisher=[[MIT Press]]|isbn=978-0-2625-1115-5}}</ref><ref>{{cite book|first = Vernon W.|last = Ruttan |date =2006 |url = https://books.google.com/books?id=Eopn-pYI1tsC&pg=PA125 |title =Is War Necessary for Economic Growth|page =125|publisher = Oxford University Press|isbn = 9780198040651}}</ref> However, the [[Internet Society]] agrees with Herzfeld in a footnote in their online article, ''A Brief History of the Internet'':

{{blockquote|It was from the RAND study that the false rumor started, claiming that the ARPANET was somehow related to building a network resistant to nuclear war. This was never true of the ARPANET, but was an aspect of the earlier RAND study of secure communication. The later work on internetworking did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks.<ref name="brief-f5">{{cite web|title=Brief History of the Internet|url=http://www.internetsociety.org/internet/what-internet/history-internet/brief-history-internet#f5 |publisher=Internet Society|access-date=|first1 = Barry M. |last1=Leiner|first2= Vinton G.|last2= Cerf|first3= David D. |last3 =Clark|first4= Robert E. |last4= Kahn|first5= Leonard |last5=Kleinrock|first6= Daniel C.|last6 = Lynch|first7 = Jon|last7= Postel|first8= Larry G.|last8= Roberts|first9 = Stephen |last9 =Wolff|date = 1997}} (footnote&nbsp;5)</ref>|author=|title=|source=}}

[[Paul Baran]], the first to put forward a theoretical model for communication using packet switching, conducted the RAND study referenced above.<ref>{{Cite journal|last=Baran|first=Paul |date=2002|title=The beginnings of packet switching: some underlying concepts|journal=IEEE Communications Magazine |url=http://web.cs.ucla.edu/~lixia/papers/Baran2002.pdf|volume=40|issue=7|pages=42–48|issn=0163-6804|doi=10.1109/MCOM.2002.1018006 |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 name="RAND corporation" /> Though the ARPANET did not exactly share Baran's project's goal, he said his work did contribute to the development of the ARPANET.<ref>{{cite news |last=Brand |first=Stewart |url=https://www.wired.com/wired/archive/9.03/baran.html |title=Founding Father |volume= 9 |magazine=[[Wired (magazine)|Wired]] |date=March 2001|issue=3|access-date=31 December 2011}}</ref> Minutes taken by Elmer Shapiro of [[Stanford Research Institute]] at the ARPANET design meeting of 9–10 October 1967 indicate that a version of Baran's routing method ("hot potato") may be used,<ref>{{cite web|website=stanford.edu |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 |url-status=dead |title= Shapiro: Computer Network Meeting of October 9–10, 1967}}</ref> consistent with the NPL team's proposal at the Symposium on Operating System Principles in Gatlinburg.<ref>{{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/page/n9/mode/2up |journal=Annals of the History of Computing |volume=9|issue=3/4|pages=239}}</ref>

Later, in the 1970s, ARPA did emphasize the goal of "command and control". According to [[Stephen J. Lukasik]], who was deputy director (1967–1970) and Director of DARPA (1970–1975):<ref>{{Cite web |title=DARPA DIRECTORS, 1958-PRESENT |url=https://www.darpa.mil/attachments/DARPA_Directors_Sheet_20201.pdf}}</ref>

{{blockquote|The goal was to exploit new computer technologies to meet the needs of military command and control against nuclear threats, achieve survivable control of US nuclear forces, and improve military tactical and management decision making.<ref>{{cite journal |last1=Lukasik |first1=Stephen J. |year=2011 |title=Why the Arpanet Was Built |doi=10.1109/MAHC.2010.11 |journal=IEEE Annals of the History of Computing |volume=33 |issue=3| pages=4–20 |s2cid=16076315}}</ref>}}

=== Implementation ===
The first four nodes were designated as a testbed for developing and debugging the [[1822 protocol]], which was a major undertaking. While they were connected electronically in 1969, network applications were not possible until the [[Network Control Protocol (ARPANET)|Network Control Protocol]] was implemented in 1970 enabling the first two host-host protocols, remote login ([[Telnet]]) and file transfer ([[FTP]]) which were specified and implemented between 1969 and 1973.<ref name=":6" /><ref name=":4" /><ref name="LINCP">{{Cite web|title=NCP, Network Control Program|url=https://www.livinginternet.com/internet/i/ii_ncp.htm|website=Living Internet|access-date=2021-03-19}}</ref> The network was declared operational in 1971. Network traffic began to grow once [[email]] was established at the majority of sites by around 1973.<ref name=":5" />

==== Initial four hosts ====
[[File:First-arpanet-imp-log.jpg|thumb|upright=1.35|First ARPANET IMP log: the first message ever sent via the ARPANET, 10:30&nbsp;pm PST on 29 October 1969 (6:30 UTC on 30 October 1969). This IMP Log excerpt, kept at UCLA, describes setting up a message transmission from the UCLA SDS Sigma 7 Host computer to the SRI SDS 940 Host computer.]]The initial ARPANET configuration linked [[UCLA]], [[Augmentation Research Center|ARC]], [[UCSB]], and the [[University of Utah School of Computing]]. The first node was created at UCLA, where [[Leonard Kleinrock]] could evaluate network performance and examine his theories on [[message delay]].<ref>{{cite thesis |author=Kleinrock, Leonard |date=December 1962 |title=Message Delay in Communication Nets with Storage |url=http://dspace.mit.edu/bitstream/handle/1721.1/11562/33840535.pdf |location=Cambridge |publisher=Massachusetts Institute of Technology |type=Thesis}}</ref><ref name=":8">{{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}} "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, using as the primary performance measure the average message delay. ... Kleinrock [in 1970] extended the theoretical approaches of [his 1961 work] to the early ARPA network."</ref><ref>{{Cite journal |last=Lukasik |first=Stephen |date=March 2011 |title=Why the Arpanet Was Built |url=https://ieeexplore.ieee.org/document/5432117 |journal=IEEE Annals of the History of Computing |volume=33 |issue=3 |pages=4–21 |doi=10.1109/MAHC.2010.11 |issn=1058-6180}}</ref> The locations were selected not only to reduce leased line costs but also because each had specific expertise beneficial for this initial implementation phase:<ref name="LIARPANETTheFirstInternet"/>

*University of California, Los Angeles (UCLA), where Kleinrock had established a Network Measurement Center (NMC), with an [[Scientific Data Systems|SDS]] [[SDS Sigma series|Sigma 7]] being the first computer attached to it;
* The Augmentation Research Center at Stanford Research Institute (now [[SRI International]]), where [[Douglas Engelbart]] had created the new [[NLS (computer system)|NLS]] system, an early [[hypertext]] system, and would run the [[Network Information Center]] (NIC), with the [[SDS 940]] that ran NLS, named "Genie", being the first host attached;
*[[University of California, Santa Barbara]] (UCSB), with the [[Glen Culler|Culler]]-Fried Interactive Mathematics Center's [[IBM]] [[System 360|360/75]], running [[OS/MVT]] being the machine attached;
* [[File:A sketch of the ARPANET in December 1969.png|thumb|A sketch of the ARPANET in December 1969. The nodes at UCLA and the Stanford Research Institute (SRI) are among those depicted.]]The [[University of Utah School of Computing]], where [[Ivan Sutherland]] had moved, running a [[Digital Equipment Corporation|DEC]] [[PDP-10]] operating on [[TENEX (operating system)|TENEX]].

The first successful host-to-host connection on the ARPANET was made between Stanford Research Institute (SRI) and UCLA, by SRI programmer Bill Duvall and UCLA student programmer Charley Kline, at 10:30&nbsp;pm PST on 29 October 1969 (6:30 UTC on 30 October 1969).<ref>{{cite news |title=Browsing history: A heritage site has been set up in Boelter Hall 3420, the room the first Internet message originated in |url=https://dailybruin.com/2011/04/01/browsing_history/|first=Jessica |last=Savio |newspaper=Daily Bruin |publisher=UCLA |date=1 April 2011 |access-date=6 June 2020}}</ref> Kline connected from UCLA's [[SDS Sigma 7]] Host computer (in Boelter Hall room 3420) to the Stanford Research Institute's [[SDS 940]] Host computer. Kline typed the command "login," but initially the SDS 940 crashed after he typed two characters. About an hour later, after Duvall adjusted parameters on the machine, Kline tried again and successfully logged in. Hence, the first two characters successfully transmitted over the ARPANET were "lo".<ref>{{Cite web|last=McMillan|first=Carolyn|date=2019-10-29|title=Lo and behold: The internet|url=https://www.universityofcalifornia.edu/news/lo-and-behold-internet|access-date=2021-03-02|website=University of California|language=en}}</ref><ref>{{cite web |title=Internet Began 35 Years Ago at UCLA with First Message Ever Sent Between Two Computers |url=http://www.engineer.ucla.edu/stories/2004/Internet35.htm |first=Chris |last=Sutton |publisher=UCLA |date=2 September 2004 |archive-url=https://web.archive.org/web/20080308120314/http://www.engineer.ucla.edu/stories/2004/Internet35.htm |archive-date=8 March 2008 |url-status=dead}}</ref><ref>{{cite web|url=https://computerhistory.org/blog/history-of-the-future-october-29-1969-fifty-years-of-a-connected-world/|title=The First 50 Years Of Living Online: ARPANET and Internet|first=Marc|last=Weber|date=October 25, 2019|work=[[Computer History Museum]] blog}}</ref> The first permanent ARPANET link was established on 21 November 1969, between the IMP at UCLA and the IMP at the Stanford Research Institute. By 5 December 1969, the initial four-node network was established.

[[Elizabeth Feinler]] created the first Resource Handbook for ARPANET in 1969 which led to the development of the ARPANET directory.<ref>{{harvnb|Evans|2018|p=112}}</ref> The directory, built by Feinler and a team made it possible to navigate the ARPANET.<ref>{{harvnb|Evans|2018|p=113}}</ref><ref>{{harvnb|Evans|2018|p=116}}</ref>

==== Network performance ====
In 1968, Roberts contracted with Kleinrock to measure the performance of the network and find areas for improvement.<ref name="Abbate20002" /><ref>{{harvnb|Hafner|Lyon|1996}}</ref><ref>{{Cite web |title=Leonard Kleinrock Helps Build The ARPANET |url=https://www.livinginternet.com/internet/i/ii_kleinrock.htm |access-date=2021-03-19 |website=Living Internet}}</ref> Building on his earlier work on [[queueing theory]] and optimization of packet delay in communication networks, Kleinrock specified mathematical models of the performance of packet-switched networks, which underpinned the development of the ARPANET as it expanded rapidly in the early 1970s.<ref name="Roberts1978" /><ref name="Gillies2000" /><ref name="Abbate20002" />

==== Growth and evolution ====
[[File:Arpanet map 1973.jpg|thumb|upright=1.4|ARPA network map 1973]]Roberts engaged [[Howard Frank (network engineer)|Howard Frank]] to consult on the topological design of the network. Frank made recommendations to increase throughput and reduce costs in a scaled-up network.<ref>{{Cite web|url=https://www.internethalloffame.org/blog/2016/04/25/howard-frank-looks-back-his-role-arpanet-designer|title=Howard Frank Looks Back on His Role as an ARPAnet Designer|date=April 25, 2016|website=Internet Hall of Fame|access-date=April 3, 2020}}</ref> By March 1970, the ARPANET reached the East Coast of the United States, when an IMP at BBN in [[Cambridge, Massachusetts]] was connected to the network. Thereafter, the ARPANET grew: 9 IMPs by June 1970 and 13 IMPs by December 1970, then 18 by September 1971 (when the network included 23 university and government hosts); 29 IMPs by August 1972, and 40 by September 1973. By June 1974, there were 46 IMPs, and in July 1975, the network numbered 57 IMPs. By 1981, the number was 213 host computers, with another host connecting approximately every twenty days.<ref name="LIARPANETTheFirstInternet" />

Support for inter-IMP circuits of up to 230.4&nbsp;kbit/s was added in 1970, although considerations of cost and IMP processing power meant this capability was not actively used.

Larry Roberts saw the ARPANET and [[National Physical Laboratory (United Kingdom)|NPL]] projects as complementary and sought in 1970 to connect them via a satellite link. [[Peter T. Kirstein|Peter Kirstein]]'s research group at [[University College London]] (UCL) was subsequently chosen in 1971 in place of NPL for the UK connection. In June 1973, a transatlantic satellite link connected ARPANET to the [[NORSAR|Norwegian Seismic Array]] (NORSAR),<ref>{{cite web |date=24 February 2020 |title=NORSAR becomes the first non-US node on ARPANET, the predecessor to today's Internet |url=https://www.norsar.no/about-us/history/arpanet-article2059-1175.html |access-date=6 June 2020 |publisher=NORSAR (Norway Seismic Array Research)}}</ref> via the Tanum Earth Station in Sweden, and onward via a terrestrial circuit to a TIP at UCL. UCL provided a gateway for interconnection of the ARPANET with British academic networks, the first international [[resource sharing]] network, and carried out some of the earliest experimental research work on internetworking.<ref>{{Cite journal |last=Kirstein |first=P.T. |date=1999 |title=Early experiences with the Arpanet and Internet in the United Kingdom |url=https://pdfs.semanticscholar.org/4773/f19792f9fce8eacba72e5f8c2a021414e52d.pdf |url-status=dead |journal=IEEE Annals of the History of Computing |volume=21 |issue=1 |pages=38–44 |doi=10.1109/85.759368 |issn=1934-1547 |archive-url=https://web.archive.org/web/20200207092443/https://pdfs.semanticscholar.org/4773/f19792f9fce8eacba72e5f8c2a021414e52d.pdf |archive-date=2020-02-07 |s2cid=1558618}}</ref>

1971 saw the start of the use of the non-ruggedized (and therefore significantly lighter) [[Honeywell 316]] as an IMP. It could also be configured as a Terminal Interface Processor (TIP), which provided [[terminal server]] support for up to 63 [[ASCII]] serial terminals through a multi-line controller in place of one of the hosts.<ref>{{cite journal|last=Kirstein|first=Peter T.|author-link=Peter T. Kirstein|date=July–September 2009|title=The Early Days of the Arpanet|url=http://muse.jhu.edu/journals/ahc/summary/v031/31.3.kirstein.html|journal=IEEE Annals of the History of Computing|volume=31|issue=3|page=67|doi=10.1109/mahc.2009.35|s2cid=28461200 |issn=1058-6180}}</ref> The 316 featured a greater degree of integration than the 516, which made it less expensive and easier to maintain. The 316 was configured with 40&nbsp;kB of core memory for a TIP. The size of core memory was later increased, to 32&nbsp;kB for the IMPs, and 56&nbsp;kB for TIPs, in 1973.

The ARPANET was demonstrated at the [[International Conference on Computer Communications]] in October 1972.

In 1975, BBN introduced IMP software running on the [[Pluribus]] [[multi-processor]]. These appeared in a few sites. In 1981, BBN introduced IMP software running on its own C/30 processor product.

=== Operation ===
ARPA was intended to fund advanced research. The ARPANET was a research project that was communications-oriented, rather than user-oriented in design.<ref name=":11">{{Cite journal|last=Frank |first=Ronald A.|date=1975-10-22|title=Security Problems Still Plague Packet-Switched Nets|journal=[[Computerworld]]|publisher=IDG Enterprise |url=https://books.google.com/books?id=wRo_E812FNcC&pg=PA18 |pages=18}}</ref> Nonetheless, in the summer of 1975, operational control of the ARPANET passed to the [[Defense Information Systems Agency#Defense Communications Agency|Defense Communications Agency]].<ref name="LIARPANETTheFirstInternet" /> At about this time, the first [[ARPANET encryption devices]] were deployed to support classified traffic.

The ''ARPANET Completion Report'', written in 1978 and published in 1981 jointly by BBN and [[DARPA]],<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}}</ref> concludes that:

{{blockquote|&nbsp;... it is somewhat fitting to end on the note that the ARPANET program has had a strong and direct feedback into the support and strength of computer science, from which the network, itself, sprang.<ref>{{cite report |chapter-url=http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA115440|title=A History of the ARPANET: The First Decade |publisher=[[BBN Technologies|Bolt, Beranek & Newman Inc.]] |location=Arlington, VA |date=1 April 1981 |chapter=III |page=132 }} section 2.3.4</ref>}}

==== CSNET, expansion ====
Access to the ARPANET was expanded in 1981 when the [[National Science Foundation]] (NSF) funded the [[Computer Science Network]] (CSNET).

==== Adoption of TCP/IP ====
[[File:First Internet Demonstration, 1977.jpg|thumb|upright=1.2|right|[[Internetworking]] demonstration, linking the ARPANET, [[PRNET]], and [[SATNET]] in 1977]]The transatlantic connectivity with NORSAR and UCL later evolved into the [[SATNET]]. The ARPANET, SATNET and [[PRNET]] were interconnected in 1977.

The DoD made [[TCP/IP]] the standard [[communication protocol]] for all military computer networking in 1980.<ref>{{Cite journal|last1=Leiner |first1=Barry M.|last2=Cerf|first2=Vinton G.|last3=Clark|first3=David D.|last4=Kahn|first4=Robert E. |last5=Kleinrock |first5=Leonard|last6=Lynch|first6=Daniel C.|last7=Postel|first7=Jon|last8=Roberts |first8=Larry G.|last9=Wolff|first9=Stephen|date=2009-10-07|title=A brief history of the internet |journal=ACM SIGCOMM Computer Communication Review |volume=39|issue=5|pages=22–31|issn=0146-4833 |s2cid=15845974|doi=10.1145/1629607.1629613}}</ref> NORSAR and University College London left the ARPANET and began using TCP/IP over SATNET in 1982.<ref name=":3" />

On January 1, 1983, known as [[Flag day (computing)|flag day]], TCP/IP protocols became the standard for the ARPANET, replacing the earlier Network Control Protocol.<ref>{{cite ietf |rfc=801 |first=Jon|last=Postel|author-link=Jon Postel |title=NCP/TCP Transition Plan |date=November 1981}}</ref><ref name="LITCPIP"/>

==== MILNET, phasing out ====
In September 1984 work was completed on restructuring the ARPANET giving U.S. military sites their own Military Network ([[MILNET]]) for unclassified defense department communications.<ref>{{cite journal |journal=Defense Data Network Newsletter |url=https://www.rfc-editor.org/rfc/museum/ddn-news/ddn-news.n26.1 |issue=26 |title=ARPANET/MILNET SPLIT - How It Will Happen |date=6 May 1983}}</ref><ref>{{cite web |url=https://apps.dtic.mil/sti/pdfs/ADA164353.pdf |title=ARPANET INFORMATION BROCHURE (NIC 50003) |publisher=Defense Communications Agency |date=December 1985}}</ref> Both networks carried unclassified information and were connected at a small number of controlled [[Gateway (telecommunications)|gateways]] which would allow total separation in the event of an emergency. MILNET was part of the [[Defense Data Network]] (DDN).<ref>{{cite book |chapter= ARPANET, the Defense Data Network, and Internet |title= The Froehlich/Kent Encyclopedia of Telecommunications |first1=Alex |last1=McKenzie |first2= Dave |last2= Walden |publisher= CRC Press |year=1991 |pages= 341–375 |volume=1 |chapter-url= https://books.google.com/books?id=gaRBTHdUKmgC&pg=PA341 |isbn= 978-0-8247-2900-4 }}</ref>

Separating the civil and military networks reduced the 113-node ARPANET by 68 nodes. After MILNET was split away, the ARPANET would continue to be used as an Internet backbone for researchers, but be slowly phased out.

=== Decommissioning ===
In 1985, the NSF funded the establishment of national supercomputing centers at several universities and provided network access and network interconnectivity with the [[NSFNET]] project in 1986. NSFNET became the Internet backbone for government agencies and universities.

The ARPANET project was formally decommissioned in 1990. The original IMPs and TIPs were phased out as the ARPANET was shut down after the introduction of the NSFNet, but some IMPs remained in service as late as July 1990.<ref>{{cite web|url=http://www.livinginternet.com/internet/i/ii_nsfnet.htm|title=NSFNET – National Science Foundation Network|website=Living Internet|access-date=2021-03-19}}</ref><ref>{{cite book|url=https://books.google.com/books?id=5O25BAAAQBAJ&q=%22arpanet%22%20%22july%201990%22&pg=PA85|title=Digital Communication|isbn=978-3-642-54331-9|last1=Meinel|first1=Christoph|last2=Sack|first2=Harald|date=21 February 2014|publisher=Springer }}</ref>

In the wake of the decommissioning of the ARPANET on 28 February 1990, Vinton Cerf wrote the following lamentation, entitled "Requiem of the ARPANET":<ref name="Abbate">{{cite book |last=Abbate |first=Janet |date=2000 |title=Inventing the Internet |location=Cambridge, MA |publisher=[[MIT Press]] |isbn=978-0-2625-1115-5 |title-link=Inventing the Internet }}</ref>

{{blockquote|
It was the first, and being first, was best,<br />
 but now we lay it down to ever rest.<br />
Now pause with me a moment, shed some tears.<br />
For [[auld lang syne]], for love, for years and years<br />
 of faithful service, duty done, I weep.<br />
 Lay down [[:wikt:thy|thy]] [[Packet (information technology)|packet]], now, O friend, and sleep.

-[[Vinton Cerf]]
}}

=== Legacy ===
[[File:ARPANET and related projects - DARPA Technical Accomplishments An Historical Review of DARPA Projects, IDA Paper P-2192, 1990.jpg|thumb|right|ARPANET and related projects. Figure from 1990.<ref>{{cite book |chapter=XX. ARPANET |url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a239925.pdf |title=DARPA Technical Accomplishments: An Historical Review of DARPA Projects |volume=1 |editor1=Sidney G. Reed |editor2=Richard H. Van Atta |editor3=Seymore J. Deitchman |id=IDA Paper P-2192 |date=1990}} This particular figure was published in 1989 or earlier.</ref>]]

The technological advancements and practical applications achieved through the ARPANET were instrumental in shaping modern computer networking including the [[Internet]]. Development and implementation of the concepts of packet switching, decentralized networks, and communication protocols, notably TCP/IP, laid the foundation for a global network that revolutionized communication, information sharing and collaborative research across the world.<ref name="G. Schneider, J. Evans, K. Pinard">{{cite book |author1=G. Schneider |url=https://books.google.com/books?id=YHwQ9WpvHfEC&pg=PA6 |title=The Internet – Illustrated |author2=J. Evans |author3=K. Pinard |date=2009 |publisher=[[Cengage Learning]] |isbn=978-0-538-75098-1 |access-date=15 August 2015}}</ref>

The ARPANET was related to many other research projects, which either influenced the ARPANET design, were ancillary projects, or spun out of the ARPANET.

Senator [[Al Gore]] authored the [[High Performance Computing and Communication Act of 1991]], commonly referred to as "The Gore Bill", after hearing the 1988 concept for a National Research Network submitted to Congress by a group chaired by [[Leonard Kleinrock]]. The bill was passed on 9 December 1991 and led to the [[National Information Infrastructure]] (NII) which Gore called the ''[[information superhighway]]''.

The ARPANET project was honored with two [[List of IEEE milestones|IEEE Milestones]], both dedicated in 2009.<ref>{{cite web|title=Milestones:Birthplace of the Internet, 1969|url=https://ethw.org/Milestones:Birthplace_of_the_Internet,_1969|access-date=28 January 2024|website=Engineering and Technology History Wiki|date=28 November 2023 }}</ref><ref>{{cite web|title=Milestones:Inception of the ARPANET, 1969|url=https://ethw.org/Milestones:Inception_of_the_ARPANET,_1969|access-date=28 January 2024|website=Engineering and Technology History Wiki|date=20 November 2023 }}</ref>

== Software and protocols ==
{{more citations needed section|date=October 2022}}

=== IMP functionality ===
Because it was never a goal for the ARPANET to support IMPs from vendors other than BBN, the IMP-to-IMP protocol and message format were not standardized. However, the IMPs did nonetheless communicate amongst themselves to perform [[link-state routing]], to do reliable forwarding of messages, and to provide remote monitoring and management functions to ARPANET's Network Control Center. Initially, each IMP had a 6-bit identifier and supported up to 4 hosts, which were identified with a 2-bit index. An ARPANET host address, therefore, consisted of both the port index on its IMP and the identifier of the IMP, which was written with either <code>port/IMP</code> notation or as a single byte; for example, the address of MIT-DMG (notable for hosting development of [[Zork]]) could be written as either <code>1/6</code> or <code>70</code>. An upgrade in early 1976 extended the host and IMP numbering to 8-bit and 16-bit, respectively.{{citation needed|date=October 2022}}

In addition to primary routing and forwarding responsibilities, the IMP ran several background programs, titled TTY, DEBUG, PARAMETER-CHANGE, DISCARD, TRACE, and STATISTICS. These were given host numbers in order to be addressed directly and provided functions independently of any connected host. For example, "TTY" allowed an on-site operator to send ARPANET packets manually via the [[teletype]] connected directly to the IMP.{{citation needed|date=October 2022}}

=== 1822 protocol ===
The starting point for host-to-host communication on the ARPANET in 1969 was the [[1822 protocol]], which defined the transmission of messages to an IMP.<ref>{{cite tech report |url=http://www.bitsavers.org/pdf/bbn/imp/BBN1822_Jan1976.pdf |title=Interface Message Processor: Specifications for the Interconnection of a Host and an IMP |id=Report No. 1822 |publisher=Bolt Beranek and Newman, Inc. (BBN)}}</ref> The message format was designed to work unambiguously with a broad range of computer architectures. An 1822 message essentially consisted of a message type, a numeric host address, and a data field. To send a data message to another host, the transmitting host formatted a data message containing the destination host's address and the data message being sent, and then transmitted the message through the 1822 hardware interface. The IMP then delivered the message to its destination address, either by delivering it to a locally connected host, or by delivering it to another IMP. When the message was ultimately delivered to the destination host, the receiving IMP would transmit a ''Ready for Next Message'' (RFNM) acknowledgment to the sending, host IMP.{{citation needed|date=October 2022}}

=== Network Control Protocol ===
Unlike modern Internet datagrams, the ARPANET was designed to reliably transmit 1822 messages, and to inform the host computer when it loses a message; the contemporary [[Internet Protocol#Reliability|IP]] is unreliable, whereas the [[Transmission Control Protocol|TCP]] is reliable. Nonetheless, the 1822 protocol proved inadequate for handling multiple connections among different applications residing in a host computer. This problem was addressed with the [[Network Control Protocol (ARPANET)|Network Control Protocol]] (NCP), which provided a standard method to establish reliable, flow-controlled, bidirectional communications links among different processes in different host computers. The NCP interface allowed [[application software]] to connect across the ARPANET by implementing higher-level [[communication protocols]], an early example of the ''protocol layering'' concept later incorporated in the [[OSI model]].<ref name="LINCP"/>

NCP was developed under the leadership of [[Steve Crocker]], then a graduate student at UCLA. Crocker created and led the Network Working Group (NWG) which was made up of a collection of graduate students at universities and research laboratories, including [[Jon Postel]] and [[Vint Cerf]] at UCLA. They were sponsored by ARPA to carry out the development of the ARPANET and the software for the host computers that supported applications.

=== Network applications ===
NCP provided a standard set of network services that could be shared by several applications running on a single host computer. This led to the evolution of ''application protocols'' that operated, more or less, independently of the underlying network service, and permitted independent advances in the underlying protocols.{{citation needed|date=October 2022}}

The various application protocols such as [[TELNET]] for remote time-sharing access and [[File Transfer Protocol]] (FTP), the latter used to enable rudimentary electronic mail, were developed and eventually ported to run over the TCP/IP protocol suite. In the 1980s, FTP for email was replaced by the [[Simple Mail Transfer Protocol]] and, later, [[Post Office Protocol|POP]] and [[IMAP]].{{citation needed|date=October 2022}}

Telnet was developed in 1969 beginning with RFC 15, extended in RFC 855.{{citation needed|date=October 2022}}

The original specification for the File Transfer Protocol was written by [[Abhay Bhushan]] and published as {{IETF RFC|114}} on 16 April 1971. By 1973, the [[File Transfer Protocol]] (FTP) specification had been defined ({{IETF RFC|354}}) and implemented, enabling file transfers over the ARPANET.{{citation needed|date=October 2022}}

In 1971, [[Ray Tomlinson]], of BBN sent the first network [[e-mail]] ({{IETF RFC|524}}, {{IETF RFC|561}}).<ref name=":5" /><ref>{{cite web|url=http://openmap.bbn.com/~tomlinso/ray/firstemailframe.html|title=The First Network Email|author=Tomlinson, Ray|publisher=BBN|url-status=dead|archive-url=https://web.archive.org/web/20060506003539/http://openmap.bbn.com/~tomlinso/ray/firstemailframe.html|archive-date=6 May 2006|access-date=6 March 2012}}</ref> An ARPA study in 1973, a year after network e-mail was introduced to the ARPANET community, found that three-quarters of the traffic over the ARPANET consisted of email messages.<ref>{{harvnb|Hafner|Lyon|1996|p=194|ps=: "found that three quarters of all traffic on the ARPANET was email"}}</ref><ref>{{Cite web |last=Edwards |first=P. N. |date=1998 |title=Virtual Machines, Virtual Infrastructures: The New Historiography of Information Technology |url=https://pne.people.si.umich.edu/PDF/isis_review.pdf |publisher=Isis essay review |page=5}}</ref><ref>{{Cite web |last=Akkad |first=Jay |title=The History of Email |url=https://sites.cs.ucsb.edu/~almeroth/classes/F04.176A/homework1_good_papers/jay-akkad.html |access-date=2023-12-30 |website=sites.cs.ucsb.edu}}</ref> E-mail remained a very large part of the overall ARPANET traffic.<ref>{{Cite book|last=Abbate|first=Janet|url=https://www.worldcat.org/oclc/44962566|title=Inventing the Internet|date=2000|publisher=[[MIT Press]]|isbn=978-0-2625-1115-5|location=Cambridge, MA|pages=106–111|oclc=44962566}}</ref>

The [[Network Voice Protocol]] (NVP) specifications were defined in 1977 ({{IETF RFC|741}}), and implemented. But, because of technical shortcomings, [[conference call]]s over the ARPANET never worked well; the contemporary [[Voice over Internet Protocol]] (packet voice) was decades away.{{citation needed|date=October 2022}}

=== TCP/IP ===
[[Stephen J. Lukasik]] directed DARPA to focus on internetworking research in the early 1970s. Bob Kahn moved from BBN to DARPA in 1972, first as program manager for the ARPANET, under Larry Roberts, then as director of the IPTO when Roberts left to found [[Telenet]]. Kahn worked on both satellite packet networks and ground-based radio packet networks, and recognized the value of being able to communicate across both. Steve Crocker, now at DARPA, and the leaders of British and French network projects founded the [[International Network Working Group]] in 1972 and, on Crocker's recommendation, [[Vint Cerf]], now on the faculty at [[Stanford University]], became its Chair.<ref name="Pelkey8.3">{{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="Hafnerp222">{{harvnb|Hafner|Lyon|1996|p=[https://archive.org/details/wherewizardsstay00haf_vgj/page/222/mode/2up 222]}}</ref><ref name=":02">{{Cite journal|last=McKenzie |first=Alexander|date=2011 |title=INWG and the Conception of the Internet: An Eyewitness Account |journal=IEEE Annals of the History of Computing|volume=33|issue=1|pages=66–71|doi=10.1109/MAHC.2011.9 |s2cid=206443072|issn=1934-1547}}</ref> This group considered how to interconnect packet switching networks with different specifications, that is, [[internetworking]]. Research led by Kahn and Cerf resulted in the formulation of the [[Transmission Control Program]],<ref name=":1" /> which incorporated concepts from the French [[CYCLADES]] project directed by [[Louis Pouzin]].<ref name=":7">{{Cite news|url=https://www.economist.com/news/technology-quarterly/21590765-louis-pouzin-helped-create-internet-now-he-campaigning-ensure-its|title=The internet's fifth man|date=2013-11-30|newspaper=The Economist|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> Its specification was written by Cerf with [[Yogen Dalal]] and Carl Sunshine at Stanford in December 1974 ({{IETF RFC|675}}). The following year, testing began through concurrent implementations at Stanford, BBN and [[University College London]].<ref name=":3">{{cite web|title=How the Internet Came to Be|url=http://elk.informatik.hs-augsburg.de/tmp/cdrom-oss/CerfHowInternetCame2B.html|author1=by Vinton Cerf, as told to Bernard Aboba|date=1993|access-date=25 September 2017|quote=We began doing concurrent implementations at Stanford, BBN, and University College London. So effort at developing the Internet protocols was international from the beginning. ... Mar '82 - Norway leaves the ARPANET and become an Internet connection via TCP/IP over SATNET. Nov '82 - UCL leaves the ARPANET and becomes an Internet connection.|url-status=dead|archive-date=26 September 2017|archive-url=https://web.archive.org/web/20170926042220/http://elk.informatik.hs-augsburg.de/tmp/cdrom-oss/CerfHowInternetCame2B.html}}</ref> At first a monolithic design, the software was redesigned as a modular protocol stack in version 3 in 1978. [[IPv4|Version 4]] was installed in the ARPANET for production use in January 1983, replacing NCP. The development of the complete [[Internet protocol suite]] by 1989, as outlined in {{IETF RFC|1122}} and {{IETF RFC|1123}}, and [[Internet protocol suite#Adoption|partnerships with the telecommunication and computer industry]] laid the foundation for the adoption of TCP/IP as a comprehensive protocol suite as the core component of the emerging [[Internet]].<ref name="LITCPIP" />

=== Password protection ===
The [[George B. Purdy#The Purdy Polynomial|Purdy Polynomial]] hash algorithm was developed for the ARPANET to protect passwords in 1971 at the request of Larry Roberts, head of ARPA at that time. It computed a polynomial of degree 2<sup>24</sup> + 17 modulo the 64-bit prime ''p'' = 2<sup>64</sup> − 59. The algorithm was later used by [[Digital Equipment Corporation]] (DEC) to hash passwords in the [[OpenVMS|VMS]] operating system and is still being used for this purpose.{{citation needed|date=October 2019}}

== Rules and etiquette ==
Because of its government funding, certain forms of traffic were discouraged or prohibited.

Leonard Kleinrock claims to have committed the first illegal act on the Internet, having sent a request for return of his electric razor after a meeting in [[England]] in 1973. At the time, use of the ARPANET for personal reasons was unlawful.<ref>{{Cite news |date=2024-01-07 |title=TALKING HEADERS |url=https://www.washingtonpost.com/archive/lifestyle/magazine/1996/08/04/talking-headers/41be42fa-d4ff-4c7b-9490-3ab441644886/ |access-date=2024-06-19 |newspaper=Washington Post |language=en-US |issn=0190-8286}}</ref><ref>''Still, tapping into the ARPANET to fetch a shaver across international lines was a bit like being a stowaway on an aircraft carrier. The ARPANET was an official federal research facility, after all, and not something to be toyed with. Kleinrock had the feeling that the stunt he'd pulled was slightly out of bounds. 'It was a thrill. I felt I was stretching the Net'.'' – {{harvnb|Hafner|Lyon|1996|loc=Chapter 7}}</ref>

In 1978, against the rules of the network, Gary Thuerk of [[Digital Equipment Corporation]] (DEC) sent out the first [[mass email]] to approximately 400 potential clients via the ARPANET. He claims that this resulted in $13 million worth of sales in DEC products, and highlighted the potential of [[email marketing]].{{citation needed|date=April 2022}}

A 1982 handbook on computing at MIT's [[AI Lab]] stated regarding network etiquette:<ref>{{Cite report |last=Stacy|first=Christopher C.|date=7 September 1982|title=Getting Started Computing at the AI Lab |series=MIT Artificial Intelligence Laboratory Working Papers |id=WP-235|hdl=1721.1/41180}}</ref>

{{blockquote|It is considered illegal to use the ARPANet for anything which is not in direct support of Government business&nbsp;... personal messages to other ARPANet subscribers (for example, to arrange a get-together or check and say a friendly hello) are generally not considered harmful&nbsp;... Sending electronic mail over the ARPANet for commercial profit or political purposes is both anti-social and illegal. By sending such messages, you can offend many people, and it is possible to get MIT in serious trouble with the Government agencies which manage the ARPANet.}}

== In popular culture ==
* ''[[Computer Networks: The Heralds of Resource Sharing]]'', a 30-minute documentary film<ref>{{cite video |people=Steven King (Producer), Peter Chvany (Director/Editor) |year=1972 |title=Computer Networks: The Heralds of Resource Sharing |url=http://documentary.operationreality.org/2011/08/27/computer-networks-the-heralds-of-resource-sharing |access-date=20 December 2011 |url-status=dead |archive-url=https://archive.today/20130415153815/http://documentary.operationreality.org/2011/08/27/computer-networks-the-heralds-of-resource-sharing |archive-date=15 April 2013  }}</ref> featuring [[Fernando J. Corbató]], [[J. C. R. Licklider]], [[Lawrence G. Roberts]], [[Bob Kahn|Robert Kahn]], Frank Heart, [[William R. Sutherland]], Richard W. Watson, [[John R. Pasta]], [[Donald W. Davies]], and economist, [[George W. Mitchell]].
* [[List of Benson episodes#Season 6 (1984–85)|"Scenario"]], an episode of the U.S. television sitcom [[Benson (TV series)|''Benson'']] (season 6, episode 20—dated February 1985), was the first incidence of a popular TV show directly referencing the Internet or its progenitors. The show includes a scene in which the ARPANET is accessed.<ref>{{cite episode |url=https://www.imdb.com/title/tt0789851/ |title=Scenario |series=Benson |season=6 |number=20 (132 of 158) |network=American Broadcasting Company (ABC), Witt/Thomas/Harris Productions |date=22 February 1985}}</ref>
* There is an [[electronic music]] artist known as "Arpanet", [[Gerald Donald]], one of the members of [[Drexciya]]. The artist's 2002 album ''Wireless Internet'' features commentary on the expansion of the internet via wireless communication, with songs such as ''[[NTT DoCoMo]]'', dedicated to the mobile communications giant based in Japan.{{citation needed |date=June 2014}}
* [[Thomas Pynchon]] mentions the ARPANET in his 2009 novel ''[[Inherent Vice]]'', which is set in Los Angeles in 1970, and in his 2013 novel ''[[Bleeding Edge (novel)|Bleeding Edge]]''.<ref>{{Cite web|title=Behold, the First Page of Thomas Pynchon's New Novel About Post-Bubble, Pre-9/11 New York, 'Bleeding Edge'|url=https://www.vice.com/en/article/7883q9/first-page-of-thomas-pynchon-novel-bleeding-edge|access-date=2022-01-25|website=www.vice.com|date=16 April 2013 |language=en}}</ref>
* The 1993 television series ''[[The X-Files]]'' featured the ARPANET in a season 5 episode, titled "[[Unusual Suspects (The X-Files)|Unusual Suspects]]". John Fitzgerald Byers offers to help Susan Modeski (known as Holly ... "just like the sugar") by hacking into the ARPANET to obtain sensitive information.<ref>{{cite episode |series=The X-Files |season=5 |number=3 |title=Unusual Suspects}}</ref>{{Better source needed |date=June 2014}}
* In the spy-drama television series ''[[The Americans]]'', a Russian scientist defector offers access to ARPANET to the Russians in a plea to not be repatriated (Season 2 Episode 5 "The Deal"). Episode 7 of Season 2 is named 'ARPANET' and features Russian infiltration to bug the network.
* In the television series ''[[Person of Interest (TV series)|Person of Interest]]'', main character Harold Finch hacked the ARPANET in 1980 using a homemade computer during his first efforts to build a prototype of the Machine.<ref>Season 2, Episode 11 "2PiR" (stylized "2<math>\pi</math>R")</ref><ref>Season 3, Episode 12 "Aletheia"</ref> This corresponds with the real life virus that occurred in October of that year that temporarily halted ARPANET functions.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/sci/tech/994700.stm|work=BBC News |first = Mark|last = Ward |department= SCI/TECH |title = Hacking: A history|date = 27 October 2000}}</ref> The ARPANET hack was first discussed in the episode [[List of Person of Interest episodes#ep34|''2PiR'' (stylized ''2<math>\pi</math>R'')]] where a computer science teacher called it the most famous hack in history and one that was never solved. Finch later mentioned it to Person of Interest Caleb Phipps and his role was first indicated when he showed knowledge that it was done by "a kid with a homemade computer" which Phipps, who had researched the hack, had never heard before.
* In the third season of the television series ''[[Halt and Catch Fire (TV series)|Halt and Catch Fire]]'', the character Joe MacMillan explores the potential commercialization of the ARPANET.

== See also ==
{{Portal|Internet}}
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
* [[.arpa]] – [[top-level domain]] used exclusively for technical infrastructure purposes
* {{Annotated link|Computer Networks: The Heralds of Resource Sharing|''Computer Networks: The Heralds of Resource Sharing''}}
* {{Annotated link|History of the Internet}}
* {{Annotated link|List of Internet pioneers}}
* {{Annotated link|OGAS}}
* [[Plan 55-A]]
* [[Protocol Wars]]
* [[Telehack]]
* {{Annotated link|Usenet}}, "A Poor Man's ARPAnet"
<!-- please keep entries in alphabetical order -->

== References ==
{{Reflist}}

=== Sources ===
* {{Cite book|url=https://books.google.com/books?id=C8ouDwAAQBAJ&q=9780735211759&pg=PP1|title=Broad Band: The Untold Story of the Women Who Made the Internet|last=Evans|first=Claire L.|publisher=Portfolio/Penguin|year=2018|isbn=978-0-7352-1175-9|location=New York}}
* {{cite book |last1=Hafner |first1=Katie |last2=Lyon |first2=Matthew |title=Where Wizards Stay Up Late: The Origins of the Internet |url=https://archive.org/details/wherewizardsstay00haf_vgj |url-access=registration |publisher=Simon and Schuster |year=1996 |isbn= 978-0-7434-6837-4}}

== Further reading ==
* {{cite book |first1=Arthur L.|last1=Norberg |first2=Judy E. |last2=O'Neill |title=Transforming Computer Technology: Information Processing for the Pentagon, 1962–1982 |publisher=Johns Hopkins University |year=1996 |pages=153–196 |isbn=978-0-8018-6369-1}}
* {{cite report |url=https://apps.dtic.mil/sti/pdfs/ADA115440.pdf|title=A History of the ARPANET: The First Decade |publisher=[[BBN Technologies|Bolt, Beranek & Newman Inc.]] |location=Arlington, VA |date=1 April 1981|archive-url=https://web.archive.org/web/20121201013642/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA115440|url-status=live|archive-date=1 December 2012}}
* {{cite book |last=Abbate |first=Janet |date=2000 |title=Inventing the Internet |location=Cambridge, MA |publisher=[[MIT Press]] |isbn=978-0-2625-1115-5 |pages=[https://archive.org/details/inventinginterne00abba/page/36 36–111] |title-link=Inventing the Internet }}
* {{cite book |first=Michael A. |last=Banks |author-link=Michael A. Banks |title=On the Way to the Web: The Secret History of the Internet and Its Founders |url=https://archive.org/details/onwaytoweb00mich |url-access=registration |publisher=APress/Springer Verlag |year=2008 |isbn=978-1-4302-0869-3}}
* {{cite book |first=Peter H. |last=Salus |author-link=Peter H. Salus |title=Casting the Net: from ARPANET to Internet and Beyond |publisher=Addison-Wesley |date=1 May 1995 |isbn=978-0-201-87674-1}}
* {{cite book |first=M. Mitchell |last=Waldrop |title=The Dream Machine: J. C. R. Licklider and the Revolution That Made Computing Personal |publisher=Viking |location=New York |date=23 August 2001 |isbn=978-0-670-89976-0 |url=https://archive.org/details/dreammachinejcrl00wald }}
* {{cite web |url=http://www.computerhistory.org/press/museum-celebrates-arpanet-anniversary.html |title=The Computer History Museum, SRI International, and BBN Celebrate the 40th Anniversary of First ARPANET Transmission |publisher=Computer History Museum |date=27 October 2009}}

=== Oral histories ===
* {{cite web |url=http://purl.umn.edu/107387 |title=Oral history interview with Robert E. Kahn |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=24 April 1990 |access-date=15 May 2008 |last1=Kahn |first1=Robert E. }} Focuses on Kahn's role in the development of computer networking from 1967 through the early 1980s. Beginning with his work at BBN, Kahn discusses his involvement as the ARPANET proposal was being written and then implemented, and his role in the public demonstration of the ARPANET. The interview continues into Kahn's involvement with networking when he moves to IPTO in 1972, where he was responsible for the administrative and technical evolution of the ARPANET, including programs in packet radio, the development of a new network protocol (TCP/IP), and the switch to TCP/IP to connect multiple networks.
* {{cite web |url=http://purl.umn.edu/107214 |title=Oral history interview with Vinton Cerf |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=24 April 1990  |access-date=1 July 2008 |last1=Cerf |first1=Vinton G. }} Cerf describes his involvement with the ARPA network, and his relationships with Bolt Beranek and Newman, Robert Kahn, Lawrence Roberts, and the Network Working Group.
* {{cite web |url=http://purl.umn.edu/107101 |title=Oral history interview with Paul Baran |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=5 March 1990  |access-date=1 July 2008 |last1=Baran |first1=Paul }} Baran describes his work at RAND, and discusses his interaction with the group at ARPA who were responsible for the later development of the ARPANET.
* {{cite web |url=http://purl.umn.edu/107411 |title=Oral history interview with Leonard Kleinrock |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=3 April 1990  |access-date=1 July 2008 |last1=Kleinrock |first1=Leonard }} Kleinrock discusses his work on the ARPANET.
* {{cite web |url=http://purl.umn.edu/107608 |title=Oral history interview with Larry Roberts |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=4 April 1989  |access-date=1 July 2008 |last1=Roberts |first1=Lawrence G. }}
* {{cite web |url=http://purl.umn.edu/107446 |title=Oral history interview with Stephen Lukasik |publisher=[[Charles Babbage Institute]] |location=University of Minnesota, Minneapolis |date=17 October 1991  |access-date=1 July 2008 |last1=Lukasik |first1=Stephen }} Lukasik discusses his tenure at the Advanced Research Projects Agency (ARPA), the development of computer networks and the ARPANET.
*{{cite web|last1=Frank|first1=Howard|date=1990-03-30|title=Oral history interview with Howard Frank |url=http://purl.umn.edu/107294|location=University of Minnesota, Minneapolis|publisher=[[Charles Babbage Institute]]|access-date=1 July 2008}} Frank describes his work on the ARPANET, including his interaction with Roberts and the IPT Office.

=== Detailed technical reference works ===
{{refbegin}}
*{{cite conference |first1=Thomas |last1=Marill |first2=Lawrence G. |last2=Roberts |s2cid=2051631 |author2-link=Lawrence Roberts (scientist) |title=Toward a cooperative network of time-shared computers |url=http://www.packet.cc/files/toward-coop-net.html |book-title=Proceedings of the November 7–10, 1966, fall joint computer conference (AFIPS '66 (Fall)) |publisher=Association for Computing Machinery |year=1966 |pages=425–431 |doi=10.1145/1464291.1464336|archive-url=https://web.archive.org/web/20020401051508/http://www.packet.cc/files/toward-coop-net.html |archive-date=2002-04-01 |url-status=dead}}
*{{cite conference |first=Lawrence G. |last=Roberts |s2cid=17409102 |title=Multiple computer networks and intercomputer communication |url=http://www.packet.cc/files/multi-net-inter-comm.html |book-title=Proceedings of the first ACM symposium on Operating System Principles (SOSP '67) |publisher=Association for Computing Machinery |year=1967 |pages=3.1–3.6 |doi=10.1145/800001.811680|archive-url=https://web.archive.org/web/20020603213900/http://www.packet.cc/files/multi-net-inter-comm.html |archive-date=2002-06-03 |url-status=dead}}
*{{cite conference |first1=D.W. |last1=Davies |author-link=Donald Davies |first2=K.A. |last2=Bartlett |first3=R.A. |last3=Scantlebury |first4=P.T. |last4=Wilkinson |s2cid=15215451 |title=A digital communication network for computers giving rapid response at remote terminals |book-title=Proceedings of the first ACM symposium on Operating System Principles (SOSP '67) |publisher=Association for Computing Machinery |year=1967 |pages=2.1–2.17 |doi=10.1145/800001.811669}}
*{{cite conference |first1=Lawrence G. |last1=Roberts |first2=Barry D. |last2=Wessler  |s2cid=9343511 |title=Computer network development to achieve resource sharing |book-title=Proceedings of the May 5–7, 1970, Spring Joint Computer Conference (AFIPS '70 (Spring)) |publisher=Association for Computing Machinery |year=1970 |pages=543–9 |doi=10.1145/1476936.1477020}}
* {{cite conference |first1=Frank |last1=Heart |author-link2=Bob Kahn |first2=Robert |last2=Kahn |first3=Severo |last3=Ornstein |author-link3=Severo Ornstein |first4=William |last4=Crowther |author-link4=William Crowther (programmer) |first5=David |last5=Walden |title=The Interface Message Processor for the ARPA Computer Network |url=http://www.walden-family.com/public/1970-imp-afips.pdf |conference=1970 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=36 |pages=551–567 |year=1970 |doi=10.1145/1476936.1477021}}
* {{cite conference |first1=Stephen |last1=Carr |first2=Stephen |last2=Crocker |author-link2=Stephen Crocker |author-link3=Vint Cerf |first3=Vinton |last3=Cerf |title=Host-Host Communication Protocol in the ARPA Network |rfc=33 |url=http://tools.ietf.org/pdf/rfc33 |conference=1970 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=36 |pages=589–598 |year=1970 |doi=10.1145/1476936.1477024}}
* {{cite conference |first1=Severo |last1=Ornstein |author-link1=Severo Ornstein |first2=Frank |last2=Heart |first3=William |last3=Crowther |author-link3=William Crowther (programmer) |first4=S. B. |last4=Russell |first5=H. K. |last5=Rising |first6=A. |last6=Michel |title=The Terminal IMP for the ARPA Computer Network |conference=1972 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=40 |pages=243–254 |year=1972|doi=10.1145/1478873.1478906 }}
* {{cite conference |first1=John |last1=McQuillan |author-link1=John M. McQuillan |first2=William |last2=Crowther |author-link2=William Crowther (programmer) |first3=Bernard |last3=Cosell |first4=David |last4=Walden |first5=Frank |last5=Heart |title=Improvements in the Design and Performance of the ARPA Network |conference=1972 Fall Joint Computer Conference part II |journal=AFIPS Proc. |volume=41 |pages=741–754 |year=1972|doi=10.1145/1480083.1480096 |doi-access=free }}
* {{cite conference |first1=Frank |last1=Heart |author-link2=Bob Kahn |first2=Robert |last2=Kahn |first3=Severo |last3=Ornstein |author-link3=Severo Ornstein |first4=William |last4=Crowther |author-link4=William Crowther (programmer) |first5=David |last5=Walden |title=The Interface Message Processor for the ARPA Computer Network |url=http://www.walden-family.com/public/1970-imp-afips.pdf |conference=1970 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=36 |pages=551–567 |year=1970 |doi=10.1145/1476936.1477021}}
* {{cite conference |first1=Stephen |last1=Carr |first2=Stephen |last2=Crocker |author-link2=Stephen Crocker |author-link3=Vint Cerf |first3=Vinton |last3=Cerf |title=Host-Host Communication Protocol in the ARPA Network |rfc=33 |url=http://tools.ietf.org/pdf/rfc33 |conference=1970 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=36 |pages=589–598 |year=1970 |doi=10.1145/1476936.1477024}}
* {{cite conference |first1=Severo |last1=Ornstein |author-link1=Severo Ornstein |first2=Frank |last2=Heart |first3=William |last3=Crowther |author-link3=William Crowther (programmer) |first4=S. B. |last4=Russell |first5=H. K. |last5=Rising |first6=A. |last6=Michel |title=The Terminal IMP for the ARPA Computer Network |conference=1972 Spring Joint Computer Conference |journal=AFIPS Proc. |volume=40 |pages=243–254 |year=1972|doi=10.1145/1478873.1478906 }}
*{{cite book |last1=Feinler |first1=E. |last2=Postel |first2=J. |title=ARPANET Protocol Handbook |publisher=SRI International |year=1976 |id=NTIS ADA027964 |oclc=2817630}}
* {{cite book |author-link1=Elizabeth J. Feinler |last1=Feinler |first1=Elizabeth J. |author-link2=Jon Postel |last2=Postel |first2=Jonathan B. |asin=B000EN742K |title=ARPANET Protocol Handbook |id=NIC 7104, NTIS ADA052594 |publisher=Network Information Center (NIC), SRI International |location=Menlo Park |date=January 1978 |oclc=7955574}}
*{{cite book |last1=Feinler |first1=E.J. |last2=Landsberden |first2=J.M. |last3=McGinnis |first3=A.C. |title=ARPANET Resource Handbook |publisher=Stanford Research Institute |year=1976 |id=NTIS ADA040452 |oclc=1110650114}}
** NTIS documents may be available from {{cite web |title=National Technical Reports Library |date=2014 |work=NTIS National Technical Information Service |publisher=U.S. Department of Commerce |url=https://ntrl.ntis.gov/NTRL/}}
* {{cite journal |first1=Larry |last1=Roberts |s2cid=26876676 |author-link1=Lawrence Roberts (scientist) |url=http://www.packet.cc/files/ev-packet-sw.html |title=The Evolution of Packet Switching |journal=Proceedings of the IEEE |date=November 1978 |doi=10.1109/PROC.1978.11141 |volume=66 |issue=11 |pages=1307–13 |access-date=3 September 2005 |archive-url=https://web.archive.org/web/20160324033133/http://www.packet.cc/files/ev-packet-sw.html |archive-date=24 March 2016 |url-status=dead  }}
* {{cite conference |first1=Larry |last1=Roberts |s2cid=24271168 |author-link1=Lawrence Roberts (scientist) |title=The ARPANET & Computer Networks |date=1986 |publisher=Association for Computing Machinery |url=http://www.packet.cc/files/arpanet-computernet.html |book-title=Proceedings of the ACM Conference on The history of personal workstations (HPW '86) |pages=51–58 |doi=10.1145/12178.12182 |isbn=978-0-89791-176-4|archive-url=https://web.archive.org/web/20160324032800/http://www.packet.cc/files/arpanet-computernet.html |archive-date=2016-03-24 }}
{{refend}}

== External links ==
{{Commons category}}
* {{cite web|url=http://som.csudh.edu/cis/lpress/history/arpamaps/ |title=ARPANET Maps 1969 to 1977 |date=4 January 1978 |publisher=[[California State University, Dominguez Hills]] (CSUDH) |access-date=17 May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120419173051/http://som.csudh.edu/cis/lpress/history/arpamaps/ |archive-date=19 April 2012 }}
* {{cite web |first=David C. |last=Walden |date=February 2003 |location=East Sandwich, Massachusetts |url=http://www.livinginternet.com/internet/i/ii_imp_walden.htm |title=Looking back at the ARPANET effort, 34 years later |website=Living Internet |access-date=2021-03-19}}
* {{cite web |url=http://www.computerhistory.org/exhibits/internet_history/ |publisher=The Computer History Museum |title=Images of ARPANET from 1964 onwards |access-date=29 August 2004}} Timeline.
* {{cite web |url=http://www.rand.org/about/history/baran.html |title=Paul Baran and the Origins of the Internet |publisher=[[RAND Corporation]] |access-date=3 September 2005}}
* {{cite web |first=Leonard |last=Kleinrock |author-link=Leonard Kleinrock |publisher=[[UCLA]] |url=http://www.lk.cs.ucla.edu/internet_first_words.html |title=The Day the Infant Internet Uttered its First Words|access-date=11 November 2004}} Personal anecdote of the first message ever sent over the ARPANET
* {{cite web |url=http://www.dougengelbart.org/firsts/internet.html |title=Doug Engelbart's Role in ARPANET History |year=2008 |access-date=3 September 2009}}
* {{cite web |url=http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2554 |title=DARPA and the Internet Revolution |first=Mitch |last=Waldrop |website=50 years of Bridging the Gap |publisher=DARPA |pages=78–85 |date=April 2008 |access-date=26 August 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120915113839/http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2554 |archive-date=15 September 2012  }}
* {{cite web |url=https://www.youtube.com/watch?v=oMvASPzXE-M | archive-url=https://web.archive.org/web/20130320025302/http://www.youtube.com/watch?v=oMvASPzXE-M| archive-date=2013-03-20 | url-status=dead|title=Robert X Cringely: A Brief History of the Internet |website=[[YouTube]] }}

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[[Category:ARPANET| ]]
[[Category:American inventions]]
[[Category:History of the Internet]]
[[Category:Computer-related introductions in 1969]]
[[Category:Internet properties established in 1969]]
[[Category:Internet properties disestablished in 1990]]
[[Category:1969 establishments in the United States]]
[[Category:Internet in the United States]]
[[Category:1990 disestablishments in the United States]]
[[Category:History of the University of California, Los Angeles]]