ARPANET (Advanced Research Projects Agency
Network) created by ARPA of the
United States Department of
Defense during the Cold War, was
the world's first operational packet
switching network, and the predecessor of the global Internet.
ARPANET logic map, March 1977.
, now the dominant
basis for both data and voice communication worldwide, was a new
and important concept in data communications. Previously, data
communication was based on the idea of circuit switching
, as in the old typical
telephone circuit, where a dedicated circuit is tied up for the
duration of the call and communication is only possible with the
single party on the other end of the circuit.
With packet switching, a system could use one communication link to
communicate with more than one machine by disassembling data into
, then gather these as packets
. Not only could the
link be shared (much as a single post box
can be used to post letters to different destinations), but each
packet could be routed independently of other packets.
A form of packet switching designed by Lincoln Laboratory
scientist Lawrence Roberts
design of ARPANET.
Background of ARPANET
The earliest ideas of a computer network intended to allow general
communication between users of various computers were formulated by
of Bolt, Beranek and Newman
August 1962, in a series of memos discussing his "Intergalactic Computer
" concept. These ideas contained almost everything that
1963, Licklider was appointed head of the Behavioral Sciences and
Command and Control programs at ARPA (as it was
then called), the United States Department of
Defense Advanced Research Projects Agency.
convinced Ivan Sutherland
this was a very important concept, although he left ARPANET before
any actual work on his vision was performed.
ARPA and Taylor continued to be interested in creating a computer
communication network, in part to allow ARPA-sponsored researchers
in various locations to use various computers which ARPA was
providing, and in part to make new software and other results
widely available quickly. Taylor had three different terminals in his
office, connected to three different computers which ARPA was
funding: one for the SDC Q-32
Monica, one for Project Genie
at the University of California,
Berkeley, and one for Multics at
Taylor later recalled:
- "For each of these three terminals, I had three different sets
of user commands. So if I was talking online with someone at S.D.C.
and I wanted to talk to someone I knew at Berkeley or M.I.T. about
this, I had to get up from the S.D.C. terminal, go over and log
into the other terminal and get in touch with them. I said, oh,
man, it's obvious what to do: If you have these three terminals,
there ought to be one terminal that goes anywhere you want to go.
That idea is the ARPANET."
Somewhat contemporaneously, a number of people had (mostly
independently) worked out various aspects of what later became
known as "packet switching", with the 1st public demonstration
being made by the UK's National Physical Laboratory
(NPL) on 5 August 1968. The people who created the ARPANET would
eventually draw on all these different sources.
Creation of ARPANET
By mid-1968, a complete plan had been prepared, and after approval
at ARPA, a Request For
(RFQ) was sent to 140 potential bidders. Most
regarded the proposal as outlandish, and only 12 companies
submitted bids, of which only four were regarded as in the top
rank. By the end of the year, the field had been narrowed to two,
and after negotiations, a final choice was made, and the contract
was awarded to BBN Technologies
7 April 1969.
BBN's proposal followed Taylor's plan closely; it called for the
network to be composed of small computers known as Interface Message Processors
(more commonly known as IMPs), what are now called routers
. The IMPs at each site performed
store-and-forward packet switching functions, and were connected to
each other using modems
connected to leased lines
(initially running at 50 kbit
/second). Host computers connected to the IMPs
via custom serial
connect to ARPANET.
BBN initially chose a ruggedized
version of Honeywell
's DDP-516 computer to
build the first-generation IMP. The 516 was originally configured
with 24 kB
of core memory (expandable) and
a 16 channel Direct Multiplex Control (DMC) direct memory access
Custom interfaces were used to connect, via the DMC, to each of the
hosts and modems. In addition to the lamps on the front panel of
the 516 there was also a special set of 24 indicator lights to show
the status of the IMP communication channels. Each IMP could
support up to four local hosts and could communicate with up to six
remote IMPs over leased lines.
The BBN team of initially only seven people were considerably
helped by the detail into which they had gone to produce their
response to the RFQ and quickly produced the first working units.
The entire system, including both hardware and the world's first
packet switching software, was designed and installed in nine
Initial ARPA deployment
First ARPANET IMP log - a record of
the first message ever sent over the ARPANET; it took place at
10:30PM on October 29, 1969.
This record is an excerpt from the "IMP Log" kept at UCLA, and
describes setting up a message transmission to go from the UCLA SDS
Sigma 7 Host computer to the SRI SDS 940 Host computer.
The initial ARPANET consisted of four IMPs
. They were installed
The first message ever sent over the ARPANET (sent over the first
host-to-host connection) occurred at 10:30 PM on October 29
. It was sent
by UCLA student programmer Charley Kline and supervised by UCLA
Professor Leonard Kleinrock. The message was sent from the UCLA SDS
Sigma 7 Host computer to the SRI SDS 940 Host computer. The message
itself was simply the word "login." The "l" and the "o" transmitted
without problem but then the system crashed. Hence, the first
message on the ARPANET was "lo". They were able to do the full
login about an hour later.
The first permanent ARPANET link was established on November 21
the IMP at UCLA and the IMP at SRI. By December 5
, the entire
4-node network was connected. When this happened, multiple
thousands of connections were opened, beyond the amount of people
at the time who could possibly connect. There is currently no
official explanation for this anomaly.
The contents of the first e-mail transmission (sent in 1971
) have long since been forgotten; in a FAQ on his
website, the sender, Ray Tomlinson (who sent the message between
two computers located side-by-side) claims that the contents were
'entirely forgettable, and I have, therefore, forgotten them', and
speculates that the message was most likely 'QWERTYUIOP' or
Software and protocol development
The starting point for host-to-host communication on the ARPANET
was the 1822 protocol
the way that a host sent messages to an ARPANET IMP. The message
format was designed to work unambiguously with a broad range of
computer architectures. Essentially, an 1822 message consisted of a
message type, a numeric host address, and a data field. To send a
data message to another host, the sending host would format a data
message containing the destination host's address and the data to
be sent, and transmit the message through the 1822 hardware
interface. The IMP would see that the message was delivered to its
destination, either by delivering it to a locally connected host or
by delivering it to another IMP. When the message was ultimately
delivered to the destination host, the IMP would send an
acknowledgment message (called Ready for Next Message
RFNM) to the sending host.
Unlike modern Internet datagrams, the ARPANET was designed to
transmit all 1822 messages reliably, or at least to be able to tell
the host when a message was lost – today’s IP
is unreliable, and TCP
Nonetheless, the 1822 protocol did not prove to be adequate by
itself for juggling multiple connections between different
applications residing on a single host. This problem was addressed
with the Network Control
or NCP, which provided a standard method to establish
reliable, flow-controlled, bidirectional communications links
between different processes on different hosts. The NCP interface
allowed application software
connect across the ARPANET implementing higher-level communication protocols
. This was an
early example of the protocol layering
incorporated into the OSI model
In 1983, TCP/IP
protocols replaced NCP as the
principal protocol of the ARPANET, and the ARPANET became just one
component of the fledgling Internet.
NCP provided a standard set of network services that could be
shared by several applications running on a single host computer.
This led to the evolution of application protocols
operated more or less independently of the underlying network
service. When the ARPANET migrated to the Internet protocols in
1983, the major application protocols migrated along with it.
- E-mail: In 1971, Ray
Tomlinson of BBN sent
the first network email. By 1973, 75% of the
ARPANET traffic was email.
- File transfer: By 1973, the File Transfer
Protocol (FTP) specification
had been defined and implemented, enabling file transfers over the
- Voice traffic: A Network Voice Protocol (NVP)
specifications was also defined (RFC 741) and then implemented, but
conference calls over the ARPANET never worked well, for technical
reasons; packet voice
would not become a workable reality for a few decades.
Growth of the network
1970, the ARPANET reached the U.S.
Coast, when an IMP at BBN itself was joined up to the network.
Thereafter, the network grew quickly: 9 IMPs by June 1970, and 13
by December; 18 by September, 1971 (at which point 23 hosts, at
universities and government research centers, were connected to the
ARPANET); 29 by August, 1972, and 40 by September, 1973.
point, two satellite links, across the Pacific and Atlantic Oceans
to Hawaii and Norway (NORSAR) had been added to the network.
Norway, a terrestrial circuit added an IMP in London to the growing
By June 1974, there were 46 IMPs, and the network reached 57 in
July, 1975. By 1981, the number of hosts had grown to 213, with a
new host being added approximately every twenty days.
After the ARPANET had been up and running for several years, ARPA
looked for another agency to hand off the network to; ARPA's
primary business was funding cutting-edge research and development,
not running a communications utility. Eventually, in July 1975, the
network was turned over to the Defense Communications Agency
also part of the Department of Defense.
In 1983, the U.S. military portion of the ARPANET was broken off as
a separate network, the MILNET
. Prior to this
there were 113 nodes on the ARPANET. After the split, that number
was 68 nodes with the remainder moving to MILNET.
Later hardware developments
Support for inter-IMP circuits of up to 230.4 kbit/s was added in
1970, although considerations of cost and IMP processing power
meant this capability was not actively used.
1971 saw the start of the use of the non-ruggedized (and therefore
significantly lighter) Honeywell 316
as an IMP. It could also be configured as a Terminal IMP (TIP),
which added support for up to 63 ASCII
terminals through a multi-line controller in place of one of the
hosts. The 316 featured a greater degree of integration than the
516, which made it less expensive and easier to maintain. The 316
was configured with 40 kB of core memory for a TIP. The size of
core memory was later increased, to 32 kB for the IMPs, and 56 kB
for TIPs, in 1973.
In 1975, BBN introduced IMP software running on the Pluribus multi-processor
. These appeared in a small
number of sites. In 1981, BBN introduced IMP software running on
its own C/30
The original IMPs and TIPs were phased out as the ARPANET was shut
down after the introduction of the NSFNet
but some IMPs remained in service as late as 1989.
Senator Albert Gore
began to craft the
Performance Computing and Communication Act of 1991
referred to as "The Gore Bill") after hearing the 1988 report
toward a National Research Network submitted to Congress by a group
chaired by UCLA professor of computer science, Leonard Kleinrock
, one of the central
creators of the ARPANET (the ARPANET, first deployed by Kleinrock
and others in 1969, is the predecessor of the Internet). The bill
was passed on December 9, 1991 and led to the National Information
(NII) which Gore
to as the "information
The ARPANET and nuclear attacks
A common semi-myth about the ARPANET states that it was designed to
be resistant to nuclear attack
writes about the
merger of technical ideas that produced the ARPANET in A Brief
History of the Internet
, and states in a note:
- It was from the RAND study that the false rumor started
claiming that the ARPANET was somehow related to building a network
resistant to nuclear war. This was never true of the
ARPANET, only the unrelated RAND study on secure voice considered
nuclear war. However, the later work on Internetting did
emphasize robustness and survivability, including the capability to
withstand losses of large portions of the underlying
The ARPANET was designed to survive network losses, but the main
reason was actually that the switching nodes and network links were
not highly reliable, even without any nuclear attacks.Charles
Herzfeld, ARPA director from 1965 to 1967, speaks about limited
computer resources helping to spur ARPANET's creation:
- The ARPANET was not started to create a Command and Control
System that would survive a nuclear attack, as many now claim.
To build such a system was clearly a major military need, but
it was not ARPA's mission to do this; in fact, we would have been
severely criticized had we tried. Rather, the ARPANET came
out of our frustration that there were only a limited number of
large, powerful research computers in the country, and that many
research investigators who should have access to them were
geographically separated from them.
For example, Iraq's Desert Storm
radar network built on technology similar to that used by
- The quick victory in the Gulf has led to the misconception
that Iraq was a poorly-defended opponent that put up little
resistance to its attackers. In fact, Iraq was equipped
with an internetted radar system and armed with 16,000
surface-to-air missiles and 7,000 antiaircraft guns The first
attacks on the radar stations to open up a safe corridor for
coalition aircraft were carried out by Apache gunships.
Support and style of management by ARPA was crucial to the success
of ARPANET. The ARPANET Completion Report, published jointly by BBN
and ARPA, concludes by stating:
- ...it is somewhat fitting to end on the note that the
ARPANET program has had a strong and direct feedback into the
support and strength of computer science, from which the network
References in film and media
- A 1985 episode of the U.S. television sitcom Benson includes a scene in which
ARPANET is accessed. This is believed to be the first incidence of
a popular TV show referencing the Internet or its progenitors.
Let the Great World Spin: A Novel, published in 2009 but
set in 1974 and written by Colum
McCann, a character named The Kid and others use ARPANET from a
Alto computer to dial phone booths in New York City in
order to hear descriptions of Philippe
Petit's tight rope walk between the World Trade
- There is an electronic music
artist known as Arpanet, Gerald Donald, one of the members
of Drexciya. The name is formatted as a
word instead of an acronym, but is still a clear nod to ARPANET.
The artist's 2002 album Wireless Internet features
commentary on the expansion of the internet via wireless
communication, with songs such as NTT
DoCoMo, dedicated to the mobile communications giant based
- Abbate, Inventing the Internet, pp.
- Norberg, O'Neill, Transforming Computer
Technology, pp. 166
- Hafner, Where Wizards Stay Up Late, pp.
- A History of the ARPANET, Chapter III, pg.132,
- Arthur Norberg, Judy E. O'Neill, Transforming Computer
Technology: Information Processing for the Pentagon, 1962-1982
(Johns Hopkins University, 1996) pp. 153-196
- A History of the ARPANET: The First Decade (Bolt,
Beranek and Newman, 1981)
- Katie Hafner and Matthew Lyon, Where Wizards Stay Up Late:
The Origins of the Internet (Simon and Schuster, 1996) ISBN
- Janet Abbate, Inventing
the Internet (MIT Press, Cambridge, 1999) pp. 36-111
- Michael A. Banks On the Way to the Web: The Secret
History of the Internet and Its Founders (APress/Springer
Verlag, 2008) ISBN 1430208694
- Peter H. Salus, Casting the Net: from ARPANET to
Internet and Beyond (Addison-Wesley, 1995)
- M. Mitchell Waldrop, The Dream Machine: J. C.
R. Licklider and the Revolution That Made Computing
Personal (Viking, New York, 2001)
Detailed technical reference works
- Larry Roberts and
Tom Merrill, Toward a Cooperative Network of Time-Shared
Computers (Fall AFIPS Conference, October 1966)
- Larry Roberts, Multiple computer networks and intercomputer
communication (ACM Symposium on Operating System
Principles. October 1967)
- D. W. Davies, K. A. Bartlett, R. A. Scantlebury, and P. T.
Wilkinson. A digital communications network for computers
giving rapid response at remote terminals (ACM Symposium on
Operating Systems Principles. October 1967)
- Larry Roberts and Barry Wessler, Computer Network Development to Achieve Resource
Sharing (Proceedings of the Spring Joint Computer
Conference, Atlantic City, New Jersey - May 1970 )
- Frank Heart, Robert Kahn, Severo Ornstein, William Crowther, David Walden, The
Interface Message Processor for the ARPA Computer Network
(1970 Spring Joint Computer Conference, AFIPS Proc. Vol. 36, pp.
- Stephen Carr, Stephen Crocker,
Vinton Cerf. Host-Host Communication
Protocol in the ARPA Network (1970 Spring Joint Computer
Conference, AFIPS Proc. Vol 36, pp. 589-598, 1970)
- Severo Ornstein, Frank Heart, William Crowther, S. B. Russell,
H. K. Rising, and A. Michel, The Terminal IMP for the ARPA
Computer Network (1972 Spring Joint Computer Conference, AFIPS
Proc. Vol. 40, pp. 243-254, 1972)
- John McQuillan, William Crowther, Bernard Cosell, David Walden,
and Frank Heart, Improvements in the Design and Performance of
the ARPA Network (1972 Fall Joint Computer Conference, AFIPS
Proc. Vol. 41, Pt. 2, pp. 741-754, 1972)
- Feinler, Elizabeth J.; Postel, Jonathan
B. ARPANET Protocol Handbook, NIC 7104 (Network
Information Center (NIC), SRI International, Menlo Park, January,
- Lawrence Roberts, The
Evolution of Packet Switching (Proceedings of the IEEE,
- Larry Roberts, The ARPANET & Computer Networks (Sept 1986
- ARPANET Maps 1967 to 1977
- Oral history interview with Robert E. Kahn, Charles
Babbage Institute, University of Minnesota, Minneapolis.
Focuses on Kahn's role in the development of computer networking
from 1967 through the early 1980s. Beginning with his work at
Bolt Beranek and Newman
(BBN), Kahn discusses his involvement as the ARPANET proposal was
being written and then implemented, and his role in the public
demonstration of the ARPANET. The interview continues into Kahn's
involvement with networking when he moves to IPTO in 1972, where he
was responsible for the administrative and technical evolution of
the ARPANET, including programs in packet radio, the development of
a new network protocol (TCP/IP), and the switch to TCP/IP to
connect multiple networks.
- Oral history interview with Vinton Cerf.
Charles Babbage Institute,
University of Minnesota, Minneapolis. Cerf describes his
involvement with the ARPA network, and his relationships with Bolt
Beranek and Newman, Robert Kahn, Lawrence Roberts, and the Network
- Oral history interview with Paul Baran.
Charles Babbage Institute,
University of Minnesota, Minneapolis. Baran describes his work at
RAND, and discusses his interaction with the group at ARPA who were
responsible for the later development of the ARPANET.
- Oral history interview with Leonard Kleinrock.
Charles Babbage Institute,
University of Minnesota, Minneapolis. Kleinrock discusses his work
on the ARPANET.
- Oral history interview with Larry Roberts. Charles Babbage Institute,
University of Minnesota, Minneapolis.
- Oral history interview with Stephen Lukasik.
Charles Babbage Institute,
University of Minnesota, Minneapolis. Lukasik discusses his tenure
at the Advanced Research Projects Agency (ARPA), the development of
computer networks and the ARPANET.
- Looking back at the ARPANET effort
- The Computer History Museum Images of ARPANET from
- A Brief History of the Internet
- Paul Baran and the Origins of the Internet
- Leonard Kleinrock's Personal History/Biography
- Personal anecdote of the first message ever sent over the
- Len Kleinrock on the Origins (subscribers only)
- Internet Chronology by Larry Roberts
- The Faces in Front of the Monitors
- Doug Engelbart's Role in ARPANET History