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Chapter 4 - Networking: Vision and Packet Switching 1959 - 1968

4.5 Donald Davies - 1965-1966

In 1965, Donald Davies, Deputy Superintendent of the Autonomics Division of the National Physical Laboratory (NPL), London, attended an International Federation for Information Processing (IFIP) Congress meeting in New York City. The IFIP meeting started Davies down a path of discovery that would lead to the same conclusions as Baran, although with special twists.

At the time, the future seemed to be time-sharing and the most influential project was Project MAC of MIT. On the suggestion of a colleague, Davies arranged a seminar at the NPL in London on November 2 and 3 with scientists from MIT to discuss Project MAC. Larry Roberts attended. Davies remembers:

We were talking not so much about communications, but about the concept of time-sharing and how it affects the way you do computing and all sorts of things. The communications aspects had interested me, because I had a history of interest in telephone switching and things like that. Nothing very much in detail was said at that meeting about solutions to the problem, but several people said how difficult it was: how you could get hour-long telephone calls in which not very much data was transmitted; what you could do about making communications more efficient and so on. During the meeting, I went over and thought about this, and it seemed to me that since the actual data rate was very variable, which is to say a few bits would pass over and then there’d be a long pause and so on, and I thought rather than opening a bandwidth for the whole time, it was sensible to treat the information in terms of short messages and simply transmit these by store-and-forward methods from one place to another. I simply sat down and did a few samples on the back of an envelope, literally, to see how this would work out. My first thought was that if you had to store messages and transmit them, there must be a delay, and this might defeat the whole purpose of the thing, which was to have rapid communications. It soon became obvious that this wasn’t so, and that if you chose fairly high data rates, by the standards of the day, and fairly short messages, the storage time was so short that it didn’t really affect your communications. Simple idea. I began to work this out.”

A week later, November 10, 1965, Davies wrote a short paper titled: “Remote On-line Data Processing and its Communication Needs.” He concluded that the delays inherent in a store-and-forward system did not need to conflict with the objective of instantaneous communications, as long as the line speed was at least 10,000 bps.

Davies, like Baran five years earlier, brought to the problem a background in digital technology. Having experience with the earliest stored-program computers (1947-1951), Davies instinctively turned to the same “message block” solution formulated by Baran. To Davies, it was an obvious solution to the mismatch between the “voice” telephone circuit and the needs of time-sharing. In his words:

A lot of effort in time sharing systems had gone into avoiding the waste of the computer’s time while it waited on the user, the thinking time, but the telephone network’s contribution to the cost had been ignored. Essentially, the communication network gave the user transmission capacity while the computer dealt in blocks of information, mostly in short units. This was the mismatch that set me thinking.

On December 8, Davies circulated an eight-page paper entitled “Proposal for the Development of a National Communications Service for On-Line Data Processing” to individuals within the telephone company (then the British Post Office) and others known to be interested in telecommunications. Davies remembers:

A few comments came back, none destructive, but none very enthusiastic. The most common remarks were that it was only message switching, which was understood, or that it would be fine, but nobody could build the necessary ‘message switches.’

Encountering no strong opposition, Davies continued work by attaching the Proposal to a research program called ‘programming research’ in order to avoid attracting too much attention.10

On March 16, 1966, Davies gave a public lecture titled: “The Future Digital Communication Network.” Typically twenty to thirty people attended such talks. A standing room only crowd of at least a hundred and twenty people showed up, mostly from the British Post Office and various telecommunications manufacturers. In the spirited discussion that followed, a few people from the Post Office proved especially negative, and would form a nucleus of opposition to Davies’s proposal to build a message-based experimental network for the Post Office (just as Licklider had been frustrated by the monopolist AT&T in the United States). Davies’ lecture was published in June 1966 as a 25-page report titled “Proposal for a Digital Communications Network.”11

In his report, Davies used the word “packet” for the first time to refer to the messages circulating over the network. He had given this the new network architecture the name that would stick: “packet switching. “

  • [10]

    A Personal View of the Origins of Packet Switching, Davies

  • [11]

    When Roberts sees Davies report, he sends Davies a copy of Baran’s internal RAND report of August 1964. Davies remembers feeling “fortunate not to have read Paul Baran’s paper when it was published because I might have considered the concept as ‘well-known’ and done nothing more.”