Donald Davies

From 1947, he worked at the National Physical Laboratory (NPL) where Alan Turing was designing the Automatic Computing Engine (ACE) computer. It is said that Davies spotted mistakes in Turing's seminal 1936 paper On Computable Numbers, much to Turing's annoyance. These were perhaps some of the first "programming" bugs in existence, even if they were for a theoretical computer, the universal Turing machine. The ACE project was overambitious and floundered, leading to Turing's departure.[9] Davies took over the project and concentrated on delivering the less ambitious Pilot ACE computer, which first worked in May 1950. A commercial spin-off, DEUCE was manufactured by English Electric Computers and became one of the best-selling machines of the 1950s.[9]

Davies also worked on applications of traffic simulation and machine translation. In the early 1960s, he worked on government technology initiatives designed to stimulate the British computer industry.

In 1965, Davies developed the idea of packet switching, dividing computer messages into packets that are routed independently across a network, possibly via differing routes, and are reassembled at the destination. Unbeknown to him, Paul Baran of the RAND Corporation in the United States was also working on a similar concept; when Baran became aware of Davies's work he acknowledged that they both had equally discovered the concept.[11][12][13]

Davies used the word "packets" after consulting with a linguist because it was capable of being translated into languages other than English without compromise.[14] Davies' key insight came in the realisation that computer network traffic was inherently "bursty" with periods of silence, compared with relatively constant telephone traffic.[15] He designed and proposed a national data network based on packet switching in his 1966 Proposal for the Development of a National Communications Service for On-line Data Processing.[16]

In 1966 he returned to the NPL at Teddington just outside London, where he headed and transformed its computing activity. He became interested in data communications following a visit to the Massachusetts Institute of Technology, where he saw that a significant problem with the new time-sharing computer systems was the cost of keeping a phone connection open for each user.[9] Davies was the first to describe the concept of an "Interface computer", in 1966, today known as a router.[17][18] He and his team were one of the first to use the term 'protocol' in a data-commutation context in 1967.[19] The NPL team also carried out simulation work on packet networks, including datagram networks.[20][21]

His work on packet switching, presented by his colleague Roger Scantlebury, initially caught the attention of the developers of ARPANET, a US defence network, at the Symposium on Operating Systems Principles in October 1967.[22] 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".[23][24] Larry Roberts of the Advanced Research Projects Agency in the United States applied Davies' concepts of packet switching in the late 1960s for the ARPANET, which went on to become a predecessor to the Internet.[9][25][6]

Davies first presented his own ideas on packet switching at a conference in Edinburgh on 5 August 1968.[26] At NPL Davies helped build a packet-switched network (Mark I NPL network). It was replaced with the Mark II in 1973, and remained in operation until 1986, influencing other research in the UK and Europe.[27][28]

Baran was happy to acknowledge that Davies had come up with the same idea as him independently. In an e-mail to Davies he wrote

You and I share a common view of what packet switching is all about, since you and I independently came up with the same ingredients.[11]

Leonard Kleinrock, a contemporary working on analysing message flow using queueing theory, developed a theoretical basis for the operation of message switching networks in his PhD thesis during 1961-2, published as a book in 1964.[29] However, Kleinrock's later claim to have developed the theoretical basis of packet switching networks is disputed,[30][31][32] including Robert Taylor,[33] Baran[34] and Davies.[35][36] Davies and Baran are recognized by historians and the U.S. National Inventors Hall of Fame for independently inventing the concept of digital packet switching used in modern computer networking including the Internet.[37][38]

Davies, along with Roger Scantlebury, participated in the International Networking Working Group from 1972, initially chaired by Vint Cerf.[39][40] He was acknowledged by Bob Kahn and Cerf in their 1974 paper on internetworking, "A Protocol for Packet Network Intercommunication".[41]

Davies relinquished his management responsibilities in 1979 to return to research. He became particularly interested in computer network security. He retired from NPL in 1984, becoming a leading consultant on data security to the banking industry.[9] Together with David O. Clayden, they designed the Message Authenticator Algorithm (MAA), an early Message Authentication Code that was adopted as international standard ISO 8731-2 in 1987. In 1987, he became a visiting professor at Royal Holloway and Bedford New College.[42]