ARPANET

The ARPANET (the word 'ARPANET' IS always used with the definite article ('the') - using naked 'ARPANET' will reveal that you are a clueless, un-educated 'noob') was the first packet-based wide-area network; so named because it was initiated, and initially funded, by ARPA.

It was intermediate between a virtual circuit network and a datagram network, but closer to the former. There was no 'call setup'; but it had what amounted to connections inside the network, data was delivered reliably and in order, and it had flow control in the network.

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.

Protocols

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 (NCP), which all the application protocols ran over.

Those included:

• FTP (early version here)
• TELNET
• MAIL (here is a much later proposal which eventually became SMTP)
• NAME/FINGER

The ARPANET later converted to using the TCP/IP protocol family, and NCP was disabled.

See also

• Port Expander
• Host table

Further reading

• 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.
• David Walden, 'IMP Software Guys', The ARPANET IMP Program: Retrospective and Resurrection, Annals of the History of Computing, Vol. 36, No. 2, April-June 2014, pp. 28-39
• Katie Hafner, Where Wizards Stay Up Late: The Origins Of The Internet, Simon & Schuster, New York, 1996 - well researched, and accessibly told, history

External links

• ARPANET RFQ - the acorn
• ARPANET Proposal - the seedling
• A History of the ARPANET: The First Decade - the tree
• BBN Report #1822, Specification for the Interconnection of a Host and an IMP - Appendix F contains the VDH specification
• ARPANET Technical Information
  • ARPANET Technical Information: Geographic Maps
  • ARPANET Technical Information: Logical Maps
  • ARPANET Technical Information: Packet Formats
  • ARPANET Technical Information: ARPANET Protocol Handbook
• Scenarios for Using the ARPANET - details of the demo at ICCC 1972
• Alexander McKenzie Interview - from the CBI oral history series; contains a wealth of detail
• Heralds of Resource Sharing - interesting contemporaneous documentary on the ARPANET
• Early Experiences with the ARPANET and INTERNET in the UK
• TCP-IP-Digest - this mailing list recorded the work to convert the ARPANET to TCP/IP
• Resurrection of the 1973 IMP code- also links to a wealth of online material