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Barry M. Leiner, Vinton G. Cerf, David D. Clark, Robert E. Kahn,
Leonard Kleinrock, Daniel C. Lynch, Jon Postel,
Lawrence G. Roberts, Stephen S. Wolff
The Past and Future History
INTERNET
T
HE
I
NTERNET HAS REVOLUTIONIZED THE COMPUTER AND COMMUNICA
-
tions world like nothing before. The telegraph, telephone, radio, and
computer have all set the stage for the Internet’s unprecedented inte-
gration of capabilities. The Internet is at once a worldwide broadcasting
capability, a mechanism for information dissemination, and a medium for
collaboration and interaction between individuals and their computers with-
out regard for geographic location.
The Internet also represents one of the most suc-
cessful examples of sustained investment and commit-
ment to research and development in information
infrastructure. Beginning with early research in packet
switching, the government, industry, and academia
have been partners in evolving and deploying this
exciting new technology. Today, terms like
lightly off the tongue of random people on the street.
1
The Internet today is a widespread information
infrastructure, the initial prototype of what is often
called the National (or Global or Galactic) Information
Infrastructure. Its history is complex and involves
many aspects—technological, organizational, and
community. And its influence reaches not only to the
technical fields of computer communications but
throughout society as we move toward increasing use
of online tools to accomplish electronic commerce,
information acquisition, and community operations.
2
Origins
The first recorded description of the social interactions
that could be enabled through networking was a series
of memos written August 1962 by J.C.R. Licklider of
MIT, discussing his “Galactic Network” concept
[
6
]
.
Licklider envisioned a globally interconnected set of
1
Perhaps this is an exaggeration due to the lead author’s residence in Silicon Valley.
2
102
February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM
of the
the science of future technology
 computers through which everyone could quickly
access data and programs from any site. In spirit, the
concept was much like the Internet today. While at
DARPA,
3
he convinced the people who would be his
successors there—Ivan Sutherland, Bob Taylor, and
MIT researcher Lawrence G. Roberts—of the impor-
tance of this networking concept.
Leonard Kleinrock of MIT published the first paper
on packet switching theory in July 1961
[
5
]
. Klein-
rock convinced Roberts of the theoretical feasibility of
communications using packets rather than circuits—a
major step toward computer networking. The other
key step was to make the computers talk to each other.
Exploring this idea in 1965 while working with
Thomas Merrill, Roberts connected the TX-2 com-
puter in Massachusetts to the Q-32 in California
through a low-speed dial-up telephone line
[
8
]
, creat-
ing the first-ever (though small) wide-area computer
network. The result of this experiment: confirmation
that time-sharing computers could work well
together, running programs and retrieving data as nec-
essary on remote machines, but that the circuit-
switched telephone system was totally inadequate for
the job. Thus confirmed was Kleinrock’s conviction of
the need for packet switching.
In late 1966, Roberts went to DARPA to develop
the computer network concept and quickly put
together a plan for the ARPANET, publishing it in
1967
[
7
]
. Bolt, Beranek and Newman Corp. (BBN),
under Frank Heart’s leadership, developed the
ARPANET switches (called IMPs), with Robert Kahn
responsible for overall system design. Howard Frank
and his team at Network Analysis Corp. worked with
Roberts to optimize the network topology and eco-
nomics. Due to Kleinrock’s early development of
packet switching theory and his focus on analysis,
design, and measurement, his Network Measurement
Center at UCLA was selected as the first node on the
ARPANET. All this came together September 1969
when BBN installed the first switch at UCLA and the
first host computer was connected. In December 1970,
the Network Working Group (NWG) under Steve
Crocker finished the initial ARPANET host-to-host
protocol, called the Network Control Protocol (NCP).
As the ARPANET sites completed implementing
NCP during 1971–1972, network users finally could
begin to develop applications.
In October 1972, a large, successful demonstration
of the ARPANET took place—the first public demon-
stration of this new network technology. Also in 1972,
electronic mail, the initial “hot” application, was intro-
duced. In March, Ray Tomlinson of BBN wrote the
basic email message send-and-read software, motivated
by ARPANET developers’ need for an easy coordina-
tion mechanism. From there, email took off as the most
popular network application and as a harbinger of the
kind of people-to-people communication activity we
see on the World-Wide Web today.
Initial Internetting Concepts
The original ARPANET grew into the Internet based
on the idea that there would be multiple independent
networks of rather arbitrary design. Beginning with
the ARPANET as the pioneering packet-switching
network, it soon grew to include packet satellite net-
works, ground-based packet radio networks, and other
networks. Today’s Internet embodies a key underlying
technical idea: open-architecture networking. In this
approach, the choice of any individual network tech-
nology is not dictated by a particular network archi-
tecture but can be selected freely by a provider and
made to interwork with the other networks through a
meta-level “internetworking architecture.” Each net-
work can be designed to fit a specific environment and
user requirements.
The idea of open-architecture networking—intro-
duced by Kahn in late 1972 shortly after arriving at
DARPA—was guided by four critical ground rules:
The Internet was conceived
in the era of time-sharing,
but has survived into the era of
personal computers, client/server
and peer-to-peer computing,
and the network computer.
• Each distinct network had to stand on its own, and
no internal changes could be required of any such
network before being connected to the Internet.
• Communications would be on a best-effort basis. If
a packet didn’t make it to the final destination, it
would quickly be retransmitted from the source.
• Black boxes (later called gateways and routers)
would be used to connect the networks. No infor-
3
The Advanced Research Projects Agency (ARPA) changed its name to Defense
Advanced Research Projects Agency (DARPA) in 1971, back to ARPA in 1993, and
back to DARPA in 1996. We refer throughout to DARPA, the current name.
COMMUNICATIONS OF THE ACM February 1997/Vol. 40, No. 2
103
 mation would be retained by the gateways about
individual flows of packets passing through them,
keeping them simple and avoiding complicated
adaptation and recovery from various failure modes.
• There would be no global control at the operations
level.
forwarding of individual packets and the separate TCP
concerned with such service features as flow control
and recovery from lost packets. For applications that
did not want the services of TCP, an alternative called
the User Datagram Protocol (UDP) was added to pro-
vide direct access to the basic IP service.
In addition to email, file transfer, and remote login,
other applications were proposed in the early days of the
Internet, including packet-based voice communication
(the precursor of Internet telephony), various models of
file and disk sharing, and early “worm” programs illus-
trating the concept of agents (and viruses). The Internet
was not designed for just one application but as a gen-
eral infrastructure on which new applications could be
conceived, exemplified later by the emergence of the
Web. The general-purpose nature of the service pro-
vided by TCP and IP makes this possible.
Kahn first began work on a communications-ori-
ented set of operating system principles while at BBN
[
4
]
. After joining DARPA and initiating the Internet
program, he asked Vinton Cerf (then at Stanford Uni-
versity) to work with him on the detailed design of the
protocol. Cerf had been deeply involved in the original
NCP design and development and was already knowl-
edgeable about interfacing to existing operating sys-
tems. So, armed with Kahn’s architectural approach to
communications and with Cerf’s NCP experience,
these two teamed up to spell out the details of what
became the Transmission Control Protocol/Internet
Proving the Ideas
DARPA funded three efforts to implement TCP: Stan-
ford (Cerf), BBN (Tomlinson), and University College
London (Peter Kirstein). The Stanford team produced a
detailed specification, yielding within about a year three
independent interoperable implementations of TCP.
This was the beginning of long-term experimenta-
tion and development of Internet concepts and tech-
nology—along with the constituent networking
technologies
[
3
]
. Each expansion has involved new
challenges. For example, the early implementations of
TCP were done for large time-sharing systems. When
desktop computers first appeared, it was thought by
some that TCP was too big and complex to run on a
personal computer. But David Clark and his research
group at MIT produced an implementation first for
the Xerox Alto (the early personal workstation devel-
oped at Xerox PARC) and then for the IBM PC, show-
ing that workstations, as well as large time-sharing
systems, could be part of the Internet.
Widespread development of local-area networks
(LANs), PCs, and workstations in the 1980s allowed
the nascent Internet to flourish. Ethernet technology
(developed by Bob Metcalfe at Xerox PARC in 1973)
is now probably the dominant network technology in
the Internet and PCs and workstations the dominant
computers. The increasing scale of the Internet also
resulted in several new approaches. For example, the
Domain Name System was invented (by Paul Mock-
apetris, then at USC’s Information Sciences Institute)
to provide a scalable mechanism for resolving hierar-
chical host names (e.g., www.acm.org) into Internet
addresses. The requirement for scalable routing
The most pressing question for the
future of the Internet is not how
the technology will change, but
how the process of change and
evolution itself will be managed.
Protocol (TCP/IP).
The original Cerf/Kahn paper
[
1
]
on the Internet
described a protocol, called TCP, providing all the
Internet’s transport and forwarding services. Kahn had
intended that TCP would support a range of transport
services—from the totally reliable sequenced delivery
of data (virtual circuit model) to a datagram service in
which the application made direct use of the underly-
ing network service, a process that could imply occa-
sional lost, corrupted, or reordered packets.
However, the initial effort to implement TCP
resulted in a version allowing only virtual circuits.
This model worked fine for file transfer and remote
login applications, but some of the early work on
advanced network applications, particularly packet
voice in the 1970s, made clear that in some cases
packet losses should not be corrected by TCP but left
to the application to deal with. This insight led to a
reorganization of the original TCP into two proto-
cols—the simple IP providing only for addressing and
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February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM
approaches led to a hierarchical model of routing, with
an Interior Gateway Protocol (IGP) used inside each
region of the Internet and an Exterior Gateway Proto-
col (EGP) used to tie the regions together. New
approaches for address aggregation, particularly class-
less interdomain routing (CIDR), were recently intro-
duced to control the size of router tables.
Another major challenge was how to propagate the
changes to the software, particularly host software.
DARPA supported the University of California at
Berkeley to investigate modifications to the Unix oper-
ating system, including incorporating TCP/IP devel-
oped at BBN. Although Berkeley later rewrote the
BBN code to more efficiently fit into the Unix system
and kernel, incorporation of TCP/IP into the Unix
BSD system proved a critical element in dispersing the
protocols to the research community. Much of the
computer science community began using Unix BSD
in their day-to-day computing environments. Looking
back, the strategy of incorporating Internet protocols
into a supported operating system for the research
community was a key element in the Internet’s suc-
cessful widespread adoption.
TCP/IP was adopted as a defense standard in 1980,
enabling the defense community to begin sharing the
DARPA Internet technology base and leading directly
to the partitioning of the military and non-military
communities. By 1983, ARPANET was being used by
a significant number of defense R&D and operational
organizations. The transition of ARPANET from NCP
to TCP/IP in 1983 permitted it to be split into a MIL-
NET supporting operational requirements and an
ARPANET supporting research needs.
Thus, by 1985, the Internet was established as a
technology supporting a broad community of
researchers and developers and was beginning to be
used by other communities for daily computer com-
munications. Email was being used broadly across sev-
eral communities, often with different systems,
demonstrating the utility of broad-based electronic
communications between people.
1970s computer networks began springing up wher-
ever funding was found for the purpose, including the
Department of Energy’s MFENET and HEPNET,
NASA’s SPAN, the computer science community’s
CSNET, the academic community’s BITNET, and
USENET based on Unix UUCP protocols. Commer-
cial networking technologies were being pursued as
well, including IBM’s SNA, Xerox’s XNS, and Digital
Equipment Corp.’s DECNET.
It remained for the British JANET (1984) and U.S.
NSFNET (1985) programs to explicitly announce their
intent to serve the entire higher education community,
regardless of discipline. In 1985, Dennis Jennings came
from Ireland for a year to lead the National Science
Foundation’s NSFNET program. He helped NSF make
a critical decision—that TCP/IP would be mandatory
for NSFNET. And when Stephen Wolff took over the
NSFNET program in 1986, he recognized the need for
a wide-area networking infrastructure to support the
general academic and research community, as well as
the need to develop a strategy for establishing such
infrastructure to ultimately be independent of direct
federal funding.
Policies and strategies were adopted to achieve that
end. So while federal agencies shared the cost of common
infrastructure, such as trans-oceanic circuits, NSF
encouraged regional networks of the NSFNET to seek
commercial, non-academic customers. And NSF
enforced an acceptable-use policy, prohibiting Backbone
use for purposes “not in support of research and educa-
tion.” The predictable (and intended) result of encour-
aging commercial network traffic at the local and
regional levels, while denying its access to national-scale
transport, was the emergence and growth of “private,”
competitive, long-haul networks, such as PSI, UUNET,
ANS CO+RE, and (later) others.
NSF’s privatization policy culminated in April
1995 with the defunding of the NSFNET Backbone.
The funds thereby recovered were (competitively)
redistributed to regional networks to buy national-
scale Internet connectivity from the now numerous,
private, long-haul networks. The Backbone had made
the transition from a network built from routers out of
the research community (David Mills’s “Fuzzball”
routers) to commercial equipment. In its eight-and-a-
half-year lifespan, the Backbone had grown from six
nodes with 56Kbps links to 21 nodes with multiple
45Mbps. It also saw the Internet grow to more than
50,000 networks on all seven continents and outer
space (with 29,000 networks in the U.S.).
Such was the weight of the NSFNET program’s
Transition to Widespread Infrastructure
At the same time Internet technology was being exper-
imentally validated and widely used by a subset of
computer science researchers, other networks and net-
working technologies were being pursued. The useful-
ness of computer networking—especially
email—demonstrated by DARPA and Department of
Defense contractors on the ARPANET was not lost on
other communities and disciplines, so that by the mid-
COMMUNICATIONS OF THE ACM February 1997/Vol. 40, No. 2
105
 ecumenism and funding ($200 million, 1986–1995)
and the quality of the protocols themselves that by
1990 when the ARPANET itself was finally decom-
missioned, TCP/IP had supplanted or marginalized
most other wide-area computer network protocols
worldwide, and IP was on its way to becoming
the
bearer service for the Global Information
Infrastructure.
infrastructure forward. Community spirit has a long
history, beginning with the early ARPANET, whose
early researchers worked as a close-knit community
(the ARPANET Working Group) to accomplish the
initial demonstrations of packet switching technology.
Likewise, the packet satellite, packet radio, and other
DARPA computer science research programs were
multi-contractor collaborative activities that used any
available mechanisms to coordinate their efforts, start-
ing with email, and adding file sharing, remote access,
and eventually Web capabilities.
In the late 1970s, recognizing that the growth of
the Internet was accompanied by the growth of the
interested research community and therefore an
increased need for coordination mechanisms, Cerf,
then manager of the DARPA Internet program,
formed several coordination bodies, including the
Internet Configuration Control Board (ICCB), chaired
by Clark. The ICCB was an invitation-only body
assisting Cerf in managing the burgeoning Internet
activity.
In 1983, when Barry Leiner took over management
of the Internet program at DARPA, he and Clark rec-
ognized that the continuing growth of the Internet
community demanded a restructuring of the coordina-
tion mechanisms.
The ICCB was disbanded and replaced by a struc-
ture of Task Forces, each focused on a particular area of
the technology (e.g., routers and end-to-end proto-
cols). The Internet Activities Board (IAB) included the
chairs of the Task Forces.
After some changing membership on the IAB, Phill
Gross became chair of a revitalized Internet Engineer-
ing Task Force (IETF)—at the time only one of the
IAB Task Forces. The growth of the Internet in the
mid-1980s resulted in vastly increased attendance at
IETF meetings, and Gross had to create substructure
to the IETF in the form of working groups.
The expanded community also meant that DARPA
was no longer the only major player when it came to
funding the Internet. In addition to NSFNET and the
various U.S. and international government-funded
activities, interest in the commercial sector was begin-
ning to grow. And in 1985, when both Kahn and
Leiner left DARPA, there was a significant decrease in
DARPA's Internet activity. The IAB was left without
a primary sponsor and so increasingly assumed the
mantle of leadership.
Continued growth resulted in even further sub-
structure within both the IAB and IETF, while growth
in the commercial sector brought increased concern
Documentation’s Key Role
A key to the rapid growth of the Internet has been free
and open access to the basic documents, especially the
specifications of the protocols. The beginnings of the
ARPANET and the Internet in the university research
community promoted the academic tradition of open
publication of ideas and results. However, the normal
cycle of traditional academic publication was too for-
mal and too slow for the dynamic exchange of ideas
essential to creating networks. In 1969, a key step was
taken by S. Crocker (then at UCLA) in establishing the
request for comments (or RFC) series of notes
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2
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.These memos were intended to be an informal fast
means of distribution for sharing ideas among network
researchers. At first the RFCs were printed on paper
and distributed via postal mail. As the File Transfer
Protocol (FTP) came into use, the RFCs were prepared
as online files and accessed via FTP. Now, the RFCs are
easily accessed via the Web at dozens of sites around
the world. SRI, in its role as Network Information
Center, maintained the online directories. Jon Postel
acted as RFC editor and as manager of centralized
administration of required protocol number assign-
ments—roles he continues to this day.
The effect of the RFCs was to create a positive feed-
back loop, so ideas or proposals presented in one RFC
would trigger other RFCs. When consensus (or a least
a consistent set of ideas) would come together, a spec-
ification document would be prepared; such specifica-
tions would then be used as the basis for
implementations by the various research teams. The
RFCs are now viewed as the “documents of record” in
the Internet engineering and standards community
and will continue to be critical to future net evolution
while furthering the net’s initial role of sharing infor-
mation about
its own design and operations.
Formation of a Broad Community
The Internet is as much a collection of communities as
a collection of technologies, and its success is largely
attributable to satisfying basic community needs as
well as utilizing the community effectively to push the
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February 1997/Vol. 40, No. 2 COMMUNICATIONS OF THE ACM
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