A Beginner's Guide to the Internet/INTERNET.ISO/text/guides/history.net/history2

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How the Internet Came to Be

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 article appears in "The Online User's Encyclopedia,"
by Bernard Aboba, Addison-Wesley, November 1993,
ISBN 0-201-62214-9


The birth of the ARPANET

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.


The birth of the Internet

Bob Kahn described the packet radio and satellite systems, and
the internet problem, which was to get host computers to
communicate across multiple packet networks without knowing the
network technology underneath. As a way of informally exploring
this problem, I ran a series of seminars at Stanford attended by
students and visitors. The students included Carl Sunshine, who
is now at Aerospace Corporation running a laboratory and
specializing in the area of protocol proof of correctness;
Richard Karp, who wrote the first TCP code and is now president
of ISDN technologies in Palo Alto. There was Judy Estrin, a
founder of Bridge Communications, which merged with 3COM, and is
now an officer at Network Computing Devices (NCD), which makes X
display terminals. Yogen Dalal, who edited the December 1974
first TCP specification, did his thesis work with this group,
and went on to work at PARC where he was one of the key
designers of the Xerox Protocols. Jim Mathis, who was involved
in the software of the small-scale LSI-11 implementations of the
Internet protocols, went on to SRI International and then to
Apple where he did MacTCP. Darryl Rubin went on to become one of
the vice presidents of Microsoft. Ron Crane handled hardware in
my Stanford lab and went on to key positions at Apple. John
Shoch went on to become assistant to the president of Xerox and
later ran their System Development Division. Bob Metcalfe
attended some of the seminars as well. Gerard Lelann was
visiting from IRIA and the Cyclades/Cigale project, and has gone
on to do work in distributed computing. We had Dag Belsnes from
University of Oslo who did work on the correctness of protocol
design; Kuninobu Tanno (from Tohoku University); and Jim Warren,
who went on to found the West Coast Computer Faire. Thinking
about computer networking problems has had a powerful influence
on careers; many of these people have gone on to make major
contributions.

The very earliest work on the TCP protocols was done at three
places. The initial design work was done in my lab at Stanford.
The first draft came out in the fall of 1973 for review by INWG
at a meeting at University of Sussex (Septemer 1973). A paper by
Bob Kahn and me appeared in May 1974 in IEEE Transactions on
Communications and the first specification of the TCP protocol
was published as an Internet Experiment Note in December 1974.
We began doing concurrent implementations at Stanford, BBN, and
University College London. So effort at developing the Internet
protocols was international from the beginning. In July 1975,
the ARPANET was transferred by DARPA to the Defense
Communications Agency (now the Defense Information Systems
Agency) as an operational network.

About this time, military security concerns became more critical
and this brought Steve Kent from BBN and Ray McFarland from DoD
more deeply into the picture, along with Steve Walker, then at
DARPA.

At BBN there were two other people: William Plummer and Ray
Tomlinson. It was Ray who discovered that our first design
lacked and needed a three-way handshake in order to distinguish
the start of a new TCP connection from old random duplicate
packets that showed up later from an earlier exchange. At
University College London, the person in charge was Peter
Kirstein. Peter had a lot of graduate and undergraduate students
working in the area, using a PDP-9 machine to do the early work.
They were at the far end of a satellite link to England.

Even at the beginning of this work we were faced with using
satellite communications technology as well as ARPANET and
packet radio. We went through four iterations of the TCP suite,
the last of which came out in 1978.

The earliest demonstration of the triple network Internet was in
July 1977. We had several people involved. In order to link a
mobile packet radio in the Bay Area, Jim Mathis was driving a
van on the San Francisco Bayshore Freeway with a packet radio
system running on an LSI-11. This was connected to a gateway
developed by .i.Internet: history of: Strazisar, Virginia;
Virginia Strazisar at BBN. Ginny was monitoring the gateway and
had artificially adjusted the routing in the system. It went
over the Atlantic via a point-to-point satellite link to Norway
and down to London, by land line, and then back through the
Atlantic Packet Satellite network (SATNET) through a Single
Channel Per Carrier (SCPC) system, which had ground stations in
Etam, West Virginia, Goonhilly Downs England, and Tanum, Sweden.
The German and Italian sites of SATNET hadn't been hooked in
yet. Ginny was responsible for gateways from packet radio to
ARPANET, and from ARPANET to SATNET. Traffic passed from the
mobile unit on the Packet Radio network across the ARPANET over
an internal point-to-point satellite link to University College
London, and then back through the SATNET into the ARPANET again,
and then across the ARPANET to the USC Information Sciences
Institute to one of their DEC KA-10 (ISIC) machines. So what we
were simulating was someone in a mobile battlefield environment
going across a continental network, then across an
intercontinental satellite network, and then back into a
wireline network to a major computing resource in national
headquarters. Since the Defense Department was paying for this,
we were looking for demonstrations that would translate to
militarily interesting scenarios. So the packets were traveling
94,000 miles round trip, as opposed to what would have been an
800-mile round trip directly on the ARPANET. We didn't lose a
bit!

After that exciting demonstration, we worked very hard on
finalizing the protocols. In the original design we didn't
distinguish between TCP and IP; there was just TCP. In the
mid-1970s, experiments were being conducted to encode voice
through a packet switch, but in order to do that we had to
compress the voice severely from 64 Kbps to 1800 bps. If you
really worked hard to deliver every packet, to keep the voice
playing out without a break, you had to put lots and lots of
buffering in the system to allow sequenced reassembly after
retransmissions, and you got a very unresponsive system. So
Danny Cohen at ISI, who was doing a lot of work on packet voice,
argued that we should find a way to deliver packets without
requiring reliability. He argued it wasn't useful to retransmit
a voice packet end to end. It was worse to suffer a delay of
retransmission.

That line of reasoning led to separation of TCP, which
guaranteed reliable delivery, from IP. So the User Datagram
Protocol (UDP) was created as the user-accessible way of using
IP. And that's how the voice protocols work today, via UDP.

Late in 1978 or so, the operational military started to get
interested in Internet technology. In 1979 we deployed packet
radio systems at Fort Bragg, and they were used in field
exercises. The satellite systems were further extended to
include ground stations in Italy and Germany. Internet work
continued in building more implementations of TCP/IP for systems
that weren't covered. While still at DARPA, I formed an Internet
Configuration Control Board chaired by David Clark from MIT to
assist DARPA in the planning and execution of the evolution of
the TCP/IP protocol suite. This group included many of the
leading researchers who contributed to the TCP/IP development
and was later transformed by my successor at DARPA, Barry
Leiner, into the Internet Activities Board (and is now the
Internet Architecture Board of the Internet Society). In 1980,
it was decided that TCP/IP would be the preferred military
protocols.

In 1982 it was decided that all the systems on the ARPANET would
convert over from NCP to TCP/IP. A clever enforcement mechanism
was used to encourage this. We used a Link Level Protocol on the
ARPANET; NCP packets used one set of one channel numbers and
TCP/IP packets used another set. So it was possible to have the
ARPANET turn off NCP by rejecting packets sent on those specific
channel numbers. This was used to convince people that we were
serious in moving from NCP to TCP/IP. In the middle of 1982, we
turned off the ability of the network to transmit NCP for one
day. This caused a lot of hubbub unless you happened to be
running TCP/IP. It wasn't completely convincing that we were
serious, so toward the middle of fall we turned off NCP for two
days; then on January 1, 1983, it was turned off permanently.
The guy who handled a good deal of the logistics for this was
Dan Lynch; he was computer center director of USC ISI at the
time. He undertook the onerous task of scheduling, planning, and
testing to get people up and running on TCP/IP. As many people
know, Lynch went on to found INTEROP, which has become the
premier trade show for presenting Internet technology.

In the same period there was also an intense effort to get
implementations to work correctly. Jon Postel engaged in a
series of Bake Offs, where implementers would shoot kamikaze
packets at each other. Recently, FTP Software has reinstituted
Bake Offs to ensure interoperability among modern vendor
products.

This takes us up to 1983. 1983 to 1985 was a consolidation
period. Internet protocols were being more widely implemented.
In 1981, 3COM had come out with UNET, which was a UNIX TCP/IP
product running on Ethernet. The significant growth in Internet
products didn't come until 1985 or so, where we started seeing
UNIX and local area networks joining up. DARPA had invested time
and energy to get BBN to build a UNIX implementation of TCP/IP
and wanted that ported into the Berkeley UNIX release in v4.2.
Once that happened, vendors such as Sun started using BSD as the
base of commercial products.

The Internet takes off

By the mid-1980s there was a significant market for
Internet-based products. In the 1990s we started to see
commercial services showing up, a direct consequence of the
NSFNet initiative, which started in 1986 as a 56 Kbps network
based on LSI-11s with software developed by David Mills, who was
at the University of Delaware. Mills called his NSFNet nodes
"Fuzzballs."

The NSFNet, which was originally designed to hook supercomputers
together, was quickly outstripped by demand and was overhauled
for T1. IBM, Merit, and MCI did this, with IBM developing the
router software. Len Bozack was the Stanford student who started
Cisco Systems. His first client: Hewlett-Packard. Meanwhile
Proteon had gotten started, and a number of other routing
vendors had emerged. Despite having built the first gateways
(now called routers), BBN didn't believe there was a market for
routers, so they didn't go into competition with Wellfleet, ACC,
Bridge, 3COM, Cisco, and others. The exponential growth of the
Internet began in 1986 with the NSFNet. When the NCP to TCP
transition occurred in 1983 there were only a couple of hundred
computers on the network. As of January 1993 there are over 1.3
million computers in the system. There were only a handful of
networks back in 1983; now there are over 10,000.

In 1988 I made a conscious decision to pursue connection of the
Internet to commercial electronic mail carriers. It wasn't clear
that this would be acceptable from the standpoint of federal
policy, but I thought that it was important to begin exploring
the question. By 1990, an experimental mail relay was running at
the Corporation for National Research Initiatives (CNRI) linking
MCI Mail with the Internet. In the intervening two years, most
commercial email carriers in the U.S. are linked to Internet and
many others around the world are following suit.

In this same time period, commercial Internet service providers
emerged from the collection of intermediate-level networks
inspired and sponsored by the National Science Foundation as
part of its NSFNet initiatives. Performance Systems
International (PSI) was one of the first, spinning off from
NYSERNet. UUNET Technologies formed Alternet; Advanced Network
and Systems (ANS) was formed by IBM, MERIT, and MCI (with its
ANS CO+RE commercial subsidiary); CERFNet was initiated by
General Atomics which also runs the San Diego Supercomputer
Center; JVNCNet became GES, Inc., offering commercial services;
Sprint formed Sprintlink; Infonet offered Infolan service; the
Swedish PTT offered SWIPNET, and comparable services were
offered in the UK and Finland. The Commercial Internet eXchange
was organized by commercial Internet service providers as a
traffic transfer point for unrestricted service.

In 1990 a conscious effort was made to link in commercial and
nonprofit information service providers, and this has also
turned out to be useful. Among others, Dow Jones, Telebase,
Dialog, CARL, the National Library of Medicine, and RLIN are now
online.

The last few years have seen internationalization of the system
and commercialization, new constituencies well outside of
computer science and electrical engineering, regulatory
concerns, and security concerns from businesses and out of a
concern for our dependence on this as infrastructure. There are
questions of pricing and privacy; all of these things are having
a significant impact on the technology evolution plan, and with
many different stakeholders there are many divergent views of
the right way to deal with various problems. These views have to
be heard and compromises worked out.

The recent rash of books about the Internet is indicative of the
emerging recognition of this system as a very critical
international infrastructure, and not just for the research and
education community.

I was astonished to see the CCITT bring up an Internet node; the
U.N. has just brought up a node, un.org; IEEE and ACM are
bringing their systems up. We are well beyond critical mass now.
The 1990s will continue this exponential growth phase. The other
scary thing is that we are beginning to see experimentation with
packet voice and packet video. I fully anticipate that an
Internet TV guide will show up in the next couple of years.

I think this kind of phenomenon is going to exacerbate the need
for understanding the economics of these systems and how to deal
with charging for use of resources. I hesitate to speculate;
currently where charges are made they are a fixed price based on
the size of the access pipe. It is possible that the continuous
transmission requirements of sound and video will require
different charging because you are not getting statistical
sharing during continuous broadcasting. In the case of
multicasting, one packet is multiplied many times. Things like
this weren't contemplated when the flat-rate charging algorithms
were developed, so the service providers may have to reexamine
their charging policies.

Concurrent with the exponential explosion in Internet use has
come the recognition that there is a real community out there.
The community now needs to recognize that it exists, that it has
a diversity of interests, and that it has responsibilities to
those who are dependent on the continued health of the network.
The Internet Society was founded in January 1992. With
assistance from the Federal Networking Council, the Internet
Society supports the IETF and IAB and educates the broad
community by holding conferences and workshops, by
proselytizing, and by making information available.

I had certain technical ambitions when this project started, but
they were all oriented toward highly flexible, dynamic
communication for military application, insensitive to
differences in technology below the level of the routers. I have
been extremely pleased with the robustness of the system and its
ability to adapt to new communications technology.

One of the main goals of the project was "IP on everything."
Whether it is frame relay, ATM, or ISDN, it should always be
possible to bring an Internet Protocol up on top of it. We've
always been able to get IP to run, so the Internet has satisfied
my design criteria. But I didn't have a clue that we would end
up with anything like the scale of what we have now, let alone
the scale that it's likely to reach by the end of the decade.

On scaling

The somewhat embarrassing thing is that the network address
space is under pressure now. The original design of 1973 and
1974 contemplated a total of 256 networks. There was only one
LAN at PARC, and all the other networks were regional or
nationwide networks. We didn't think there would be more than
256 research networks involved. When it became clear there would
be a lot of local area networks, we invented the concept of
Class A, B, and C addresses. In Class C there were several
million network IDs. But the problem that was not foreseen was
that the routing protocols and Internet topology were not well
suited for handling an extremely large number of network IDs. So
people preferred to use Class B and subnetting instead. We have
a rather sparsely allocated address space in the current
Internet design, with Class B allocated to excess and Class A
and C allocated only lightly.

The lesson is that there is a complex interaction between
routing protocols, topology, and scaling, and that determines
what Internet routing structure will be necessary for the next
ten to twenty years.

When I was chairman of the Internet Activities Board and went to
the IETF and IAB to characterize the problem, it was clear that
the solution had to be incrementally deployable. You can deploy
something in parallel, but then how do the new and old
interwork? We are seeing proposals of varying kinds to deal with
the problem. Some kind of backward compatibility is highly
desirable until you can't assign 32-bit address space.
Translating gateways have the defect that when you're halfway
through, half the community is transitioned and half isn't, and
all the traffic between the two has to go through the
translating gateway and it's hard to have enough resources to do
this.

It's still a little early to tell how well the alternatives will
satisfy the requirements. We are also dealing not only with the
scaling problem, but also with the need not to foreclose
important new features, such as concepts of flows, the ability
to handle multicasting, and concepts of accounting.

I think that as a community we sense varying degrees of pressure
for a workable set of solutions. The people who will be most
instrumental in this transition will be the vendors of routing
equipment and host software, and the offerers of Internet
services. It's the people who offer Internet services who have
the greatest stake in assuring that Internet operation continues
without loss of connectivity, since the value of their service
is a function of how many places you can communicate with. The
deployability of alternative solutions will determine which is
the most attractive. So the transition process is very
important.

On use by other networks

The Domain Name System (DNS) has been a key to the scaling of
the Internet, allowing it to include non-Internet email systems
and solving the problem of name-to-address mapping in a smooth
scalable way. Paul Mockapetris deserves enormous credit for the
elegant design of the DNS, on which we are still very dependent.
Its primary goal was to solve the problems with the host.txt
files and to get rid of centralized management. Support for Mail
eXchange (MX) was added after the fact, in a second phase.

Once you get a sufficient degree of connectivity, it becomes
more advantageous to link to this highly connected thing and
tunnel through it rather than to build a system in parallel. So
BITNET, FidoNet, AppleTalk, SNA, Novell IPX, and DECNet
tunneling are a consequence of the enormous connectivity of the
Internet.

The Internet has become a test bed for development of other
protocols. Since there was no lower level OSI infrastructure
available, Marshall Rose proposed that the Internet could be
used to try out X.400 and X.500. In RFC 1006, he proposed that
we emulate TP0 on top of TCP, and so there was a conscious
decision to help higher-level OSI protocols to be deployed in
live environments before the lower-level protocols were
available.

It seems likely that the Internet will continue to be the
environment of choice for the deployment of new protocols and
for the linking of diverse systems in the academic, government,
and business sectors for the remainder of this decade and well
into the next.
.