Editing ARPANET (section)

=== 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|url-access=subscription}}</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.