The National Physical Laboratory Network (NPL Network or NPL Data Communications Network) was a computer network operated by a team from the National Physical Laboratory in England. Following a pilot experiment during 1967, 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 until 1986. The NPL network, followed by ARPANET in the United States, were the first two computer networks that implemented packet switching, and were interconnected in the early 1970s.
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History of the network
The network was proposed by Donald Davies, who was later was appointed to head of the NPL Division of Computer Science, as Proposal for the Development of a National Communications Service for On-line Data Processing at NPL during 1965, during 1966 he headed a team which produced a design for the network. The next year (1967) a written version of the proposal entitled NPL Data Network was presented by Roger Scantlebury at a conference at Gatlinburg of the proceedings of the Association for Computing Machinery, which 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".
Packet switching
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. Packet switching was used to produce an experimental network using a Honeywell 516 node. According to Zakon, NPL under Davies was the earliest organisation that created a packet-switching network.
Later developments
The NPL network was later interconnected with other networks, including the ARPANET in 1973. The NPL network used a line speed of 768 kbit/s in 1967. Influenced by this, the proposed line speed for ARPANET was upgraded from 2.4 kbit/s to 50 kbit/s and a similar packet format adopted.