Donald Watts Davies, CBE FRS (7 June 1924 – 28 May 2000) was a British computer scientist and an early developer of the Internet. He worked at the UK National Physical Laboratory (NPL).

Between 1965 and 1967, he created modern data communication methods, including packet switching, high-speed routers, layered communication protocols, hierarchical computer networks, and the foundation of the end-to-end principle. These ideas are used today in computer networks around the world. In 1966, he imagined a "single network" that could handle both data and telephone communications. He proposed and studied a commercial national data network in the United Kingdom and built the first working example of packet switching in the NPL network in 1969 to show how the technology worked. Many large-scale packet-switched networks developed in the late 1960s and 1970s closely followed his original 1965 design. His work influenced the ARPANET in the United States and the CYCLADES project in France, and was essential to the creation of the Internet, which connects many networks together.

Davies’ research was done independently of Paul Baran’s work in the United States, where Baran had similar ideas in the early 1960s. Baran also contributed to the ARPANET project after Davies’ team brought attention to his findings.

Early life

Davies was born in Treorchy, in the Rhondda Valley, Wales. His father worked as a clerk at a coalmine but passed away a few months later. His mother moved back to her hometown of Portsmouth, England, with Donald and his twin sister. There, he attended school at the Southern Grammar School for Boys.

He earned a BSc degree in physics in 1943 from Imperial College London. Afterward, he joined the war effort and worked as an assistant to Klaus Fuchs on the nuclear weapons Tube Alloys project at Birmingham University. Later, he returned to Imperial College and received a first-class degree in mathematics in 1947. He was also honored with the Lubbock memorial Prize, which recognized him as the top mathematician in his class.

In 1955, he married Diane Burton. Together, they had one daughter and two sons.

National Physical Laboratory

From 1947, Davies worked at the National Physical Laboratory (NPL) in Teddington, near London, where Alan Turing was designing the Automatic Computing Engine (ACE) computer. Davies found errors in Turing's important 1936 paper titled On Computable Numbers, which upset Turing. These errors may have been among the first programming mistakes ever made, even though they were for a theoretical computer called the universal Turing machine. The ACE project was too ambitious and had problems, leading to Turing leaving the project. Davies took over and focused on creating a simpler version of the ACE called the Pilot ACE, which worked for the first time in May 1950. A commercial version called DEUCE, made by English Electric Computers, became one of the most popular computers in the 1950s.

Davies also worked on using computers to simulate traffic and translate languages. In the early 1960s, he helped develop government technology programs to support the British computer industry.

In 1965, Davies became interested in data communication after giving a talk at the Massachusetts Institute of Technology. He noticed that time-sharing computer systems had a problem: keeping phone lines open for each user was expensive. Davies realized that computer network traffic had periods of silence, unlike steady telephone traffic. He used the idea of time-sharing to create a new concept called packet switching. He called the small message parts "packets" after discussing the word with a linguist, as it could be translated into other languages without losing meaning.

In 1966, Davies returned to NPL and became the head of the Computer Science Division. He proposed a national data network based on packet switching in a report titled Proposal for the Development of a National Communications Service for On-line Data Processing. This work described the first ideas for high-speed switching nodes, now called routers, and interface computers. Davies used queueing theory to show that users could get fast responses from a network. This helped prove that computer networks could work well. In this report, he predicted a "single network" for both data and telephone communications.

Davies and his team wrote the first modern communication protocols in a 1967 memorandum titled A Protocol for Use in the NPL Data Communications Network, written by Roger Scantlebury and Keith Bartlett. His work on packet switching, presented by Scantlebury, caught the attention of ARPANET developers at a conference in 1967. The network design used a structure with local networks connected to a larger network. To handle packet order changes and lost messages, Davies believed error control should be handled by users, an idea now called the end-to-end principle. Scantlebury noted that NPL's ideas were more advanced than those in the United States. Larry Roberts of the U.S. Department of Defense used Davies' packet switching concepts for ARPANET, which later became part of the Internet.

In July 1968, NPL demonstrated real and simulated networks at an event in London. Davies presented his packet switching ideas at a conference in Edinburgh in August 1968. In 1969, he traveled to Japan to give nine lectures on packet switching, ending with a discussion with about 80 people.

From 1968 to 1969, Davies oversaw the construction of the first packet-switching network, which became operational in 1970 as the Mark I NPL network. It was upgraded to the Mark II in 1973 with a layered protocol system and remained in use until 1986. NPL also studied packet networks, analyzing data traffic and congestion in large networks. These early efforts were shown in the 1972 film Computer Networks: The Heralds of Resource Sharing. Davies' ideas influenced research worldwide, including France's CYCLADES project.

In a 1978 article on packet switching, Bob Kahn, the guest editor, quoted Davies' reflections on ten years of experience with packet communication networks.

Davies and his team, including Derek Barber and Roger Scantlebury, researched protocols for connecting different networks. They joined the International Network Working Group starting in 1972. Davies and Scantlebury were acknowledged by Vint Cerf and Bob Kahn in their 1974 paper on internetworking, A Protocol for Packet Network Intercommunication.

In 1973, Davies and Barber published Communication Networks for Computers. They discussed the "battle for access standards" between datagrams and virtual circuits at a 1975 conference, with Barber stating that the lack of standard interfaces for packet-switched networks was creating challenges for users.

At NPL, Davies tested connecting networks by translating between different protocols and using a common protocol. His research showed that using a single protocol was more reliable than translating between different ones. In 1979, Davies published Computer Networks and Their Protocols, where he noted:

— Donald Davies (1979)

For many years, network engineers debated which protocols would best support computer networks, a conflict known as the Protocol Wars. It was unclear which approach would lead to the most effective networks.

In 1979, Davies stepped down from management to focus on research. He studied computer network security and developed patents for secure communication methods, including those used in smart cards.

Davies retired from NPL in 1984 and became a consultant on data security for the banking industry. He published a book on the topic that year. In 1983, he and David O. Clayden designed the Message Authenticator Algorithm (MAA), one of the first widely accepted message authentication code algorithms. It became an international standard (ISO 8731-2) in 1987.

Epilogue

At first, Davies was unaware that Paul Baran, a researcher at the RAND Corporation in the United States, had also worked on a similar idea in the early 1960s. Baran’s design focused on voice communication and used low-cost electronics without software in the switches. In 1966, when Davies learned about Baran’s work, he recognized that both he and Baran had independently discovered the concept of packet switching. Davies and his team then cited Baran’s earlier published research.

Baran was pleased to note that Davies had reached the same conclusion on his own and that Davies was the first to put the idea into practice.

Leonard Kleinrock, a researcher studying how delays in message delivery could be calculated using queueing theory, created a mathematical model for message switching networks in his PhD thesis between 1961 and 1962. This work was later published as a book in 1964. However, since the late 1990s, Kleinrock’s claim that he developed the theoretical foundation for packet switching networks has been challenged by other Internet pioneers, including Robert Taylor, Baran, and Davies.

Legacy

Donald Davies and Paul Baran are known by historians and the U.S. National Inventors Hall of Fame for inventing separately the idea of digital packet switching, which is used in modern computer networks, including the Internet.

Larry Roberts stated that the computer networks developed in the 1970s were almost identical to Davies' original 1965 design in almost every way. Davies' work on data communications and computer network design is considered essential technology for creating the Internet, which is a worldwide network of connected computers; that is, a network of networks.

Awards and honours

Davies was honored as a Distinguished Fellow of the British Computer Society (BCS) in 1975. He received a CBE, a British honor, in 1983. In 1987, he became a Fellow of the Royal Society.

In 1974, he was given the John Player Award by the BCS. In 1985, he received a medal from the John von Neumann Computer Society in Hungary.

In 2000, Davies shared the first IEEE Internet Award. In 2007, he was inducted into the National Inventors Hall of Fame. In 2012, he was inducted into the Internet Hall of Fame by the Internet Society.

In 2001, Davies was given a lifetime achievement award for his work on secure communications for smart cards.

The National Physical Laboratory (NPL) supports a gallery at The National Museum of Computing. The gallery, opened in 2009, displays information about the development of packet switching and "Technology of the Internet."

In July 2013, a blue plaque honoring Davies was unveiled in Treorchy.

Books

• Davies, Donald Watts (1963), Digital Techniques, Electronic User Series, Blackie & Son
• Davies, Donald Watts; Barber, Derek L. A. (1973), Communication Networks for Computers, Computing and Information Processing, John Wiley & Sons, ISBN 9780471198741
• Davies, Donald Watts (1979), Computer Networks and Their Protocols, Computing and Information Processing, John Wiley & Sons, ISBN 9780471997504 with co-authors W. Price, D. Barber, and C. Solomonides
• 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