The ARPANET was the first packet-based wide-area network; so named because it was initiated, and initially funded, by ARPA.
It consisted of minicomputers called Interface Message Processors ('IMPs', for short) running specialized packet switching code, joined together with synchronous serial lines; host computers were initially connected to the IMPs by special bit-serial 1822 interfaces.
(The 1822 'Local Host' and 'Distant Host' interface variants had maximum lengths of about 100 feet and 2,000 feet respectively; to allow connection of hosts at much greater distances, a wholly new interface, the 'Very Distant Host', was eventually added. It used a synchronous seral line, at the hardware level; on the IMP end, the existing serial line interfaces were used.)
Later on, customized IMP variants called Terminal Interface Processors ('TIPs', for short) were added to the ARPANET; these provided groups of asynchronous serial lines to which could be attached terminals, which allowed users at the terminals access to the hosts attached to the ARPANET.
The protocol suite used on the early ARPANET included:
- The Host-to-IMP Protocol, the bottom layer; specified in BBN Report #1822 (below; multiple editions over time)
- ICP, Initial connection protocol
- Host-to-Host Protocol (early version here)
These protocols formed the Network Control Protocol, which all the application protocols ran over.
- FTP (early version here)
- MAIL (here is a much later proposal which eventually became SMTP)
- F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, "The interface message processor for the ARPA computer network", Proceedings AFIPS, 1970 SJCC, Vol. 36, pp. 551-567.
- J.M. McQuillan, W.R. Crowther, B.P. Cosell, D.C. Walden, and F.E. Heart, "Improvements in the Design and Performance of the ARPA Network", Proceedings AFIPS, 1972 FJCC, Vol. 40, pp. 741-754.
- John M. McQuillan, David C. Walden, "The ARPA Network Design Decisions", in "Computer Networks", Vol. 1, No. 5, August 1977, pp. 243-289.
- BBN Report #1822, Specification for the Interconnection of a Host and an IMP - Appendix F contains the VDH specification
- ARPANET Technical Information
- Early Experiences with the ARPANET and INTERNET in the UK