Based on designs first proposed by Donald Davies in 1965, elements of the first version of the network, the Mark I, became operational during 1969 then fully operational in 1970, and the Mark II version operated from 1973 until 1986. The NPL network, followed by the wide area ARPANET in the United States, were the first two computer networks that implemented packet switching.
In 1965, Donald Davies, who was later appointed to head of the NPL Division of Computer Science, proposed a 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. The design was the first to describe the concept of an "Interface computer", today known as a router.
The next year (1967) 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 equipment (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. 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".
Larry Roberts incorporated these concepts into the design for the ARPANET. The NPL network proposed a line speed of 768 kbit/s. 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.
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. Davies independently arrived at the same model in 1965 and named it packet switching. 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. NPL under Davies was the earliest organisation that created a packet switching network.
Davies gave the first public presentation of packet switching on 5 August 1968. Packet switching was used to produce an experimental network using a Honeywell 516 node. Elements of the first version of the network, Mark I, became operational during 1969 then fully operational in 1970, and the Mark II version operated from 1973. The NPL team also carried out simulation work on the performance of packet networks, including datagram networks. The local area NPL network and the wide area ARPANET in the United States, were the first two computer networks that implemented packet switching.
The NPL network was later interconnected with other networks, including the ARPANET via University College London in 1973 and CYCLADES via the European Informatics Network (EIN) in 1976. In 1976, 12 computers and 75 terminal devices were attached, and more were added. The network remained in operation until 1986, influencing other research in the UK and Europe.
Alongside Donald Davies, the NPL team included Derek Barber, Roger Scantlebury, Peter Wilkinson, Keith Bartlett, and Brian Aldous.
One of the first uses of the term 'protocol' in a data-commutation 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.
NPL was also involved in internetworking research. Derek Barber was appointed director of the European COST 11 project which became the European Informatics Network (EIN) while Scantlebury led the UK technical contribution.
Davies, Scantlebury and Barber were members of the International Networking Working Group (INWG) which developed a protocol for internetworking. The EIN protocol helped to launch the proposed INWG standard. Vint Cerf and Bob Kahn acknowledged Davies and Scantlebury in their 1974 paper "A Protocol for Packet Network Intercommunication".
NPL research investigated connecting existing networks, which creates a "basic dilemma" since a common host protocol would require restructuring the existing networks. 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.
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.
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
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.
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.
Although he was aware of the concept of packet switching, Roberts was not sure how to implement it in a large network.
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. May 30, 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 cr 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.
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.
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.