NPL network schematic

The NPL network, or NPL Data Communications Network, was a local area computer network operated by a team from the National Physical Laboratory in London that pioneered the concept of packet switching.

Based on designs first conceived by Donald Davies in 1965, development work began in 1968. Elements of the first version of the network, the Mark I, became operational during 1969 then fully operational in January 1970, and the Mark II version operated from 1973 until 1986. The NPL network and the ARPANET in the United States were the first two computer networks that implemented packet switching and the NPL network was the first to use high-speed links.


In 1965, Donald Davies, who was later appointed to head of the NPL Division of Computer Science, proposed a commercial national data network based on packet switching in Proposal for the Development of a National Communications Service for On-line Data Processing. After the proposal was not taken up nationally, during 1966 he headed a team which produced a design for a local network to serve the needs of NPL and prove the feasibility of packet switching.[1] The design was the first to describe the concept of an "Interface computer", today known as a router.[2]

The next year, a written version of the proposal entitled NPL Data Network was presented by Roger Scantlebury at the Symposium on Operating Systems Principles. It described how computers (nodes) used to transmit signals (packets) would be connected by electrical links to re-transmit the signals between and to the nodes, and interface computers would be used to link node networks to so-called time-sharing computers and other users. The interface computers would transmit multiplex signals between networks, and nodes would switch transmissions while connected to electrical circuitry functioning at a rate of processing amounting to mega-bits.[3][4] In Scantlebury's report following the conference, he noted "It would appear that the ideas in the NPL paper at the moment are more advanced than any proposed in the USA".[5][6][7]

Larry Roberts incorporated these concepts into the design for the ARPANET.[8][9][10] The NPL network initially proposed a line speed of 768 kbit/s.[11] Influenced by this, the planned line speed for ARPANET was upgraded from 2.4 kbit/s to 50 kbit/s and a similar packet format adopted.[12][13]

Packet switching

NPL network packet

The first theoretical foundation of packet switching was the work of Paul Baran, in which data was transmitted in small chunks and routed independently by a method similar to store-and-forward techniques between intermediate networking nodes.[14] Davies independently arrived at the same model in 1965 and named it packet switching.[15] He chose the term "packet" after consulting with an NPL linguist because it was capable of being translated into languages other than English without compromise.[16] Davies gave the first public presentation of packet switching on 5 August 1968.[17]

Network development

The NPL team used their packet switching concept to produce an experimental network using a Honeywell 516 node. Coincidentally, this was the same computer chosen by the ARPANET to serve as Interface Message Processors. Construction began in 1968.[18]

Elements of the first version of the network, Mark I NPL Network, became operational during 1969 then fully operational in January 1970.[3] The local area NPL network and the wide area ARPANET in the United States were the first two computer networks that implemented packet switching.[19][20] The network later used high-speed T1 links (1.544 Mbit/s line rate), the first computer network to do so.[21][22][23] The Mark II version operated from 1973.[3][4]

The NPL team also carried out simulation work on the performance of packet networks, including datagram networks.[3][24]

The NPL network was later interconnected with other networks, including CYCLADES and the European Informatics Network (EIN) in 1976.[3]

In 1976, 12 computers and 75 terminal devices were attached,[25] and more were added. The network remained in operation until 1986, influencing other research in the UK and Europe.[3]

Alongside Donald Davies, the NPL team included Derek Barber, Roger Scantlebury, Peter Wilkinson, Keith Bartlett, and Brian Aldous.[26]

Protocol development

NPL network model

One of the first uses of the term "protocol" in a data commutations context occurs in a memorandum entitled A Protocol for Use in the NPL Data Communications Network written by Roger Scantlebury and Keith Bartlett in April 1967.[27] A further publication by Bartlett in 1968 introduced the concept of an "alternating bit protocol" (later used by the ARPANET and the EIN)[28][29] and described the need for three levels of data transmission (roughly corresponding to the lower levels of the seven-layer OSI model that emerged a decade later). The Mark II version, which operated from 1973, used such a "layered" protocol architecture. The NPL team also introduced the idea of "protocol verification".[21]

The NPL network was a testbed for internetworking research throughout the 1970s. Davies, Scantlebury and Barber were active members of the International Networking Working Group (INWG) formed in 1972. Vint Cerf and Bob Kahn acknowledged Davies and Scantlebury in their 1974 paper "A Protocol for Packet Network Intercommunication".[30] Derek Barber was appointed director of the European COST 11 project played a leading part in proposing the European Informatics Network (EIN) and led the project while Scantlebury led the UK technical contribution.[21][31][32][33] The EIN protocol helped to launch the INWG work,[29][34] which proposed an "international end to end protocol" in 1975.[35][36][37]

NPL research investigated the "basic dilemma" involved in internetworking; that is, a common host protocol would require restructuring existing networks if they were not designed to use the same protocol. NPL connected with the European Informatics Network by translating between two different host protocols while the NPL connection to the Post Office Experimental Packet Switched Service used a common host protocol in both networks. This work confirmed establishing a common host protocol would be more reliable and efficient.[38]

Davies and Barber published "Communication networks for computers" in 1973 and "Computer networks and their protocols" in 1979.[39][40] They spoke at the Data Communications Symposium in 1975 about the "battle for access standards" between datagrams and virtual circuits, with Barber saying the "lack of standard access interfaces for emerging public packet-switched communication networks is creating 'some kind of monster' for users".[41] For a long period of time, the network engineering community was polarized over the implementation of competing protocol suites, commonly known as the Protocol Wars. It was unclear which type of protocol would result in the best and most robust computer networks.[42]

Davies' research at NPL later focused on data security for computer networks.[43]

Modern recognition

NPL sponsors a gallery, opened in 2009, about the development of packet switching and "Technology of the Internet" at The National Museum of Computing at Bletchley Park.[26]

See also


  1. ^ Pelkey, James (2007), "NPL Network and Donald Davies 1966 - 1971", Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968-1988, retrieved 13 April 2016
  2. ^ Roberts, Dr. Lawrence G. (May 1995). "The ARPANET & Computer Networks". Archived from the original on 24 March 2016. Retrieved 13 April 2016. Then in June 1966, Davies wrote a second internal paper, "Proposal for a Digital Communication Network" In which he coined the word packet,- a small sub part of the message the user wants to send, and also introduced the concept of an "Interface computer" to sit between the user equipment and the packet network.
  3. ^ a b c d e f Hempstead, C.; Worthington, W., eds. (2005). Encyclopedia of 20th-Century Technology. Routledge. pp. 573–5. ISBN 9781135455514. Retrieved 15 August 2015.
  4. ^ a b A Hey, G Pápay (8 December 2014). The Computing Universe: A Journey through a Revolution. Cambridge University Press. ISBN 978-0521766456. Retrieved 16 August 2015.(source: Roger Scantlebury - p.201)
  5. ^ "Oral-History:Donald Davies & Derek Barber". Retrieved 13 April 2016. the ARPA network is being implemented using existing telegraphic techniques simply because the type of network we describe does not exist. It appears that the ideas in the NPL paper at this moment are more advanced than any proposed in the USA
  6. ^ Naughton, John (2015). "8 Packet post". A Brief History of the Future: The origins of the Internet. Hachette UK. ISBN 978-1474602778. they lacked one vital ingredient. Since none of them had heard of Paul Baran they had no serious idea of how to make the system work. And it took an English outfit to tell them.
  7. ^ Barber, Derek (Spring 1993). "The Origins of Packet Switching". The Bulletin of the Computer Conservation Society (5). ISSN 0958-7403. Retrieved 6 September 2017. Roger actually convinced Larry that what he was talking about was all wrong and that the way that NPL were proposing to do it was right. I've got some notes that say that first Larry was sceptical but several of the others there sided with Roger and eventually Larry was overwhelmed by the numbers.
  8. ^ "Computer Pioneers - Donald W. Davies". IEEE Computer Society. Retrieved 20 February 2020. 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.; "A Flaw In The Design". The Washington Post. 30 May 2015. 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.
  9. ^ Gillies, J.; Cailliau, R. (2000). How the Web was Born: The Story of the World Wide Web. Oxford University Press. pp. 23–26. ISBN 0192862073.
  10. ^ F.E. Froehlich, A. Kent (14 November 1990). The Froehlich/Kent Encyclopedia of Telecommunications: Volume 1 - Access Charges in the U.S.A. to Basics of Digital Communications. CRC Press. p. 344. ISBN 0824729005.
  11. ^ Kaminow, Ivan; Li, Tingye (22 May 2002). Optical Fiber Telecommunications IV-B: Systems and Impairments. Elsevier. p. 29. ISBN 978-0-08-051319-5.
  12. ^ Abbate, Janet (2000). Inventing the Internet. MIT Press. p. 38. ISBN 0262261332.
  13. ^ Roberts, Dr. Lawrence G. (May 1995). "The ARPANET & Computer Networks". Archived from the original on 14 February 2019. Retrieved 16 June 2019.
  14. ^ Winston, Brian (2002). Media,Technology and Society: A History: From the Telegraph to the Internet. Routledge. pp. 323–327. ISBN 1134766327.
  15. ^ Scantlebury, Roger (25 June 2013). "Internet pioneers airbrushed from history". The Guardian. Retrieved 1 August 2015.
  16. ^ Harris, Trevor, Who is the Father of the Internet? The case for Donald Watts Davies, p. 6, retrieved 10 July 2013
  17. ^ "The accelerator of the modern age". BBC News. 5 August 2008. Retrieved 19 May 2009.
  18. ^ Scantlebury, R. A.; Wilkinson, P.T. (1974). "The National Physical Laboratory Data Communications Network". Proceedings of the 2nd ICCC 74. pp. 223–228.
  19. ^ John S, Quarterman; Josiah C, Hoskins (1986). "Notable computer networks". Communications of the ACM. 29 (10): 932–971. doi:10.1145/6617.6618. S2CID 25341056. The first packet-switching network was implemented at the National Physical Laboratories in the United Kingdom. It was quickly followed by the ARPANET in 1969.
  20. ^ Roberts, Lawrence G. (November 1978). "The Evolution of Packet Switching". Archived from the original on 24 March 2016. Retrieved 9 April 2016.
  21. ^ a b c Cambell-Kelly, Martin (1987). "Data Communications at the National Physical Laboratory (1965-1975)". Annals of the History of Computing. 9 (3/4): 221–247. doi:10.1109/MAHC.1987.10023. S2CID 8172150. Transmission of packets of data over the high-speed lines
  22. ^ Roberts, Lawrence G. (November 1978). "The evolution of packet switching" (PDF). Proceedings of the IEEE. 66 (11): 1307–13. doi:10.1109/PROC.1978.11141. S2CID 26876676. Both Paul Baran and Donald Davies in their original papers anticipated the use of T1 trunks
  23. ^ Guardian Staff (25 June 2013). "Internet pioneers airbrushed from history". The Guardian. ISSN 0261-3077. Retrieved 31 July 2020. This was the first digital local network in the world to use packet switching and high-speed links.
  24. ^ Pelkey, James. "6.3 CYCLADES Network and Louis Pouzin 1971-1972". Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968-1988.
  25. ^ "The National Physical Laboratory Data Communications Netowrk". 1974. Retrieved 5 September 2017.
  26. ^ a b "Technology of the Internet". The National Museum of Computing. Retrieved 3 October 2017.
  27. ^ Naughton, John (2015). A Brief History of the Future. Orion. ISBN 978-1-4746-0277-8.
  28. ^ "ARPANET is now 50 years old | Inria". Retrieved 10 November 2022.
  29. ^ a b Davies, Donald Watts (1979). Computer networks and their protocols. John Wiley & Sons. pp. 464. ISBN 9780471997504.
  30. ^ Cerf, V.; Kahn, R. (1974). "A Protocol for Packet Network Intercommunication" (PDF). IEEE Transactions on Communications. 22 (5): 637–648. CiteSeerX doi:10.1109/TCOM.1974.1092259. ISSN 1558-0857. 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.
  31. ^ Barber, D L. (1975). "Cost project 11". ACM SIGCOMM Computer Communication Review. 5 (3): 12–15. doi:10.1145/1015667.1015669. S2CID 28994436.
  32. ^ Scantlebury, Roger (1986). "X.25 - past, present and future". In Stokes, A. V. (ed.). Communications Standards: State of the Art Report. Pergamon. pp. 203–216. ISBN 978-1-4831-6093-1.
  33. ^ "EIN (European Informatics Network)". Computer History Museum. Retrieved 5 February 2020.
  34. ^ Hardy, Daniel; Malleus, Guy (2002). Networks: Internet, Telephony, Multimedia: Convergences and Complementarities. Springer Science & Business Media. p. 505. ISBN 978-3-540-00559-9.
  35. ^ McKenzie, Alexander (2011). "INWG and the Conception of the Internet: An Eyewitness Account". IEEE Annals of the History of Computing. 33 (1): 66–71. doi:10.1109/MAHC.2011.9. ISSN 1934-1547. S2CID 206443072.
  36. ^ Scantlebury, Roger (25 June 2013). "Internet pioneers airbrushed from history". The Guardian. Retrieved 1 August 2015.
  37. ^ Scantlebury, Roger (8 January 2010). "How we nearly invented the internet in the UK". New Scientist. Retrieved 7 February 2020.
  38. ^ Abbate, Janet (2000). Inventing the Internet. MIT Press. p. 125. ISBN 978-0-262-51115-5.
  39. ^ Davies, Donald Watts; Barber, Derek L. A. (1973), Communication networks for computers, Computing and Information Processing, John Wiley & Sons, ISBN 9780471198741
  40. ^ Davies, Donald Watts (1979). Computer networks and their protocols. Internet Archive. Chichester, [Eng.] ; New York : Wiley. pp. 456–477. ISBN 9780471997504.
  41. ^ Frank, Ronald A. (22 October 1975). "Battle for Access Standards Has Two Sides". Computerworld. IDG Enterprise: 17–18.
  42. ^ Davies, Howard; Bressan, Beatrice (26 April 2010). A History of International Research Networking: The People who Made it Happen. John Wiley & Sons. ISBN 978-3-527-32710-2.
  43. ^ Davies, D. W.; Price, W. L. (1984), Security for computer networks: an introduction to data security in teleprocessing and electronic funds transfer, New York: John Wiley & Sons, ISBN 978-0471921370

Further reading

Primary sources