How the Internet came to be: The birth of the ARPANET (idea)

by Vinton Cerf, as told to Bernard Aboba
Copyright (C) 1993 Vinton Cerf. All rights reserved. May be reproduced in any medium for noncommercial purposes.
This node is a part of How the Internet Came to Be node

My involvement began when I was at UCLA doing graduate work from 1967 to 1972. There were several people at UCLA at the time studying under Jerry Estrin, and among them was Stephen Crocker. Stephen was an old high-school friend, and when he found out that I wanted to do graduate work in computer science, he invited me to interview at UCLA.

When I started graduate school, I was originally looking at multiprocessor hardware and software. Then a Request For Proposal came in from the Defense Advanced Research Projects Agency, DARPA. The proposal was about packet switching, and it went along with the packet-switching network that DARPA was building.

Several UCLA faculty were interested in the RFP. Leonard Kleinrock had come to UCLA from MIT, and he brought with him his interest in that kind of communications environment. His thesis was titled Communication Networks: Stochastic Flow and Delay, and he was one of the earliest queuing theorists to examine what packet-switch networking might be like. As a result, the UCLA people proposed to DARPA to organize and run a Network Measurement Center for the ARPANET project.

This is how I wound up working at the Network Measurement Center on the implementation of a set of tools for observing the behavior of the fledgling ARPANET. The team included Stephen Crocker; Jon Postel, who has been the RFC editor from the beginning; Robert Braden, who was working at the UCLA computer center; Michael Wingfield, who built the first interface to the Internet for the Xerox Data System Sigma 7 computer, which had originally been the Scientific Data Systems (SDS) Sigma 7; and David Crocker, who became one of the central figures in electronic mail standards for the ARPANET and the Internet. Mike Wingfield built the BBN 1822 interface for the Sigma 7, running at 400 Kbps, which was pretty fast at the time.

Around Labor Day in 1969, BBN delivered an Interface Message Processor (IMP) to UCLA that was based on a Honeywell DDP 516, and when they turned it on, it just started running. It was hooked by 50 Kbps circuits to two other sites (SRI and UCSB) in the four-node network: UCLA, Stanford Research Institute (SRI), UC Santa Barbara (UCSB), and the University of Utah in Salt Lake City.

We used that network as our first target for studies of network congestion. It was shortly after that I met the person who had done a great deal of the architecture: Robert Kahn, who was at BBN, having gone there from MIT. Bob came out to UCLA to kick the tires of the system in the long haul environment, and we struck up a very productive collaboration. He would ask for software to do something, I would program it overnight, and we would do the tests.

One of the many interesting things about the ARPANET packet switches is that they were heavily instrumented in software, and additional programs could be installed remotely from BBN for targeted data sampling. Just as you use trigger signals with oscilloscopes, the IMPs could trigger collection of data if you got into a certain state. You could mark packets and when they went through an IMP that was programmed appropriately, the data would go to the Network Measurement Center.

There were many times when we would crash the network trying to stress it, where it exhibited behavior that Bob Kahn had expected, but that others didn't think could happen. One such behavior was reassembly lock-up. Unless you were careful about how you allocated memory, you could have a bunch of partially assembled messages but no room left to reassemble them, in which case it locked up. People didn't believe it could happen statistically, but it did. There were a bunch of cases like that.

My interest in networking was strongly influenced by my time at the Network Measurement Center at UCLA.

Meanwhile, Larry Roberts had gone from Lincoln Labs to DARPA, where he was in charge of the Information Processing Techniques Office. He was concerned that after building this network, we could do something with it. So out of UCLA came an initiative to design protocols for hosts, which Steve Crocker led.

In April 1969, Steve issued the very first Request For Comment. He observed that we were just graduate students at the time and so had no authority. So we had to find a way to document what we were doing without acting like we were imposing anything on anyone. He came up with the RFC methodology to say, "Please comment on this, and tell us what you think."

Initially, progress was sluggish in getting the protocols designed and built and deployed. By 1971 there were about nineteen nodes in the initially planned ARPANET, with thirty different university sites that ARPA was funding. Things went slowly because there was an incredible array of machines that needed interface hardware and network software. We had Tenex systems at BBN running on DEC-10s, but there were also PDP8s, PDP-11s, IBM 360s, Multics, Honeywell... you name it. So you had to implement the protocols on each of these different architectures. In late 1971, Larry Roberts at DARPA decided that people needed serious motivation to get things going. In October 1972 there was to be an International Conference on Computer Communications, so Larry asked Bob Kahn at BBN to organize a public demonstration of the ARPANET.

It took Bob about a year to get everybody far enough along to demonstrate a bunch of applications on the ARPANET. The idea was that we would install a packet switch and a Terminal Interface Processor or TIP in the basement of the Washington Hilton Hotel, and actually let the public come in and use the ARPANET, running applications all over the U.S.

A set of people who are legendary in networking history were involved in getting that demonstration set up. Bob Metcalfe was responsible for the documentation; Ken Pogran who, with David Clark and Noel Chiappa, was instrumental in developing an early ring-based local area network and gateway, which became Proteon products, narrated the slide show; Crocker and Postel were there. Jack Haverty, who later became chief network architect of Oracle and was an MIT undergraduate, was there with a holster full of tools. Frank Heart who led the BBN project; David Walden; Alex McKenzie; Severo Ornstein; and others from BBN who had developed the IMP and TIP.

The demo was a roaring success, much to the surprise of the people at AT&T who were skeptical about whether it would work. At that conference a collection of people convened: Donald Davies from the UK, National Physical Laboratory, who had been doing work on packet switching concurrent with DARPA; Remi Despres who was involved with the French Reseau Communication par Paquet (RCP) and later Transpac, their commercial X.25 network; Larry Roberts and Barry Wessler, both of whom later joined and led BBN's Telenet; Gesualdo LeMoli, an Italian network researcher; Kjell Samuelson from the Swedish Royal Institute; John Wedlake from British Telecom; Peter Kirstein from University College London; Louis Pouzin who led the Cyclades/Cigale packet network research program at the Institute Recherche d'Informatique et d'Automatique (IRIA, now INRIA, in France). Roger Scantlebury from NPL with Donald Davies may also have been in attendance. Alex McKenzie from BBN almost certainly was there.

I'm sure I have left out some and possibly misremembered others. There were a lot of other people, at least thirty, all of whom had come to this conference because of a serious academic or business interest in networking.

At the conference we formed the International Network Working Group or INWG. Stephen Crocker, who by now was at DARPA after leaving UCLA, didn't think he had time to organize the INWG, so he proposed that I do it.

I organized and chaired INWG for the first four years, at which time it was affiliated with the International Federation of Information Processing (IFIP). Alex Curran, who was president of BNR, Inc., a research laboratory of Bell Northern Research in Palo Alto, California, was the U.S. representative to IFIP Technical Committee 6. He shepherded the transformation of the INWG into the first working group of 6, working group 6.1 (IFIP WG 6.1).

In November 1972, I took up an assistant professorship post in computer science and electrical engineering at Stanford. I was one of the first Stanford acquisitions who had an interest in computer networking. Shortly after I got to Stanford, Bob Kahn told me about a project he had going with SRI International, BBN, and Collins Radio, a packet radio project. This was to get a mobile networking environment going. There was also work on a packet satellite system, which was a consequence of work that had been done at the University of Hawaii, based on the ALOHA-Net, done by Norman Abramson, Frank Kuo, and Richard Binder. It was one of the first uses of multiaccess channels. Bob Metcalfe used that idea in designing Ethernet before founding 3COM to commercialize it.