Everything about The Arpanet totally explained
The
ARPANET (
Advanced Research Projects Agency Network) developed by
DARPA of the
United States Department of Defense, was the world's first operational
packet switching network, and the predecessor of the global
Internet.
Packet switching, 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 datagraphs, 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.
This idea was thought up by
Paul Baran, of the
RAND Corporation (a government agency)for the U.S. Air Force to do a study on how it could maintain its command and control over its missiles and bombers, after a nuclear attack. This was to be a military research network that could survive a nuclear strike, decentralized so that if any locations (cities) in the U.S. were attacked, the military could still have control of nuclear arms for a counter-attack.
Quote from Paul Baran:
"Packet switching is the breaking down of data into datagrams or packets that are labeled to indicate the origin and the destination of the information and the forwarding of these packets from one computer to another computer until the information arrives at its final destination computer. This was crucial to the realization of a computer network. If packets are lost at any given point, the message can be resent by the originator."
Background of the ARPANET
The earliest ideas of a computer network intended to allow general communication between users of various computers were formulated by
J.C.R. Licklider of
Bolt, Beranek and Newman (BBN) in August 1962, in a series of memos discussing his "
Intergalactic Computer Network" concept. These ideas contained almost everything that the
Internet is today.
In October 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. He then convinced
Ivan Sutherland and
Bob Taylor that this was a very important concept, although he left ARPA 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 quickly make new software and other results widely available. Taylor had three different terminals in his office, connected to three different computers which ARPA was funding: one for the
SDC Q-32 in
Santa Monica, one for
Project Genie at the
University of California, Berkeley, and one for
Multics at
MIT. Taylor later recalled:
» "For each of these three terminals, I'd 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'd 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've these three terminals, there ought to be one terminal that goes anywhere you want to go. That idea is the ARPAnet."
(External Link
).
Somewhat contemporaneously, a number of people had (mostly independently) worked out various aspects of what later became known as "packet switching"; the people who created the ARPANET would eventually draw on all these different sources.
Creation of the ARPANET
By the mid-1968, a complete plan had been prepared, and after approval at ARPA, a
Request For Quotation (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 on
7 April,
1969.
BBN's proposal followed Roberts' plan closely; it called for the network to be composed of small computers known as
Interface Message Processors (more commonly known as IMPs). 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
bit-serial interfaces to 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 control unit. 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 small team at BBN (initially only seven people), helped considerably by the detail they'd gone into to produce their response to the RFQ, 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 months.
Initial ARPA deployment
The initial ARPANET consisted of four IMPs. They were installed at:
The first permanent ARPANET link was established on
November 21,
1969, between the IMP at UCLA and the IMP at SRI. By
December 5,
1969, the entire 4-node network was connected
(External Link).
The first message ever to be sent over the ARPANET (sent over the first host-to-host connection) occurred at 10:30 PM on October 29, 1969. 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.
Software and protocol development
The starting point for host-to-host communication on the ARPANET was the
1822 protocol which defined 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 or 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. Nonetheless, the 1822 protocol didn't 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 Program 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 to connect across the ARPANET implementing higher-level
communication protocols. This was an early example of the
protocol layering concept 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.
Network Applications
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 that 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 (External Link). 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 ARPANET.
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 wouldn't become a workable reality for a few decades.
Growth of the network
In March, 1970, the ARPANET reached the U.S. East Coast, when an IMP at BBN itself was joined up to the network. Thereafter, the network grew quickly: 9 IMPs by June of 1970, and 13 by December; 18 by September, 1971 (at which point twenty-three hosts, at universities and government research centers, were connected to the ARPANET); 29 by August, 1972, and 40 by September, 1973.
At that point, two satellite links, across the Pacific and Atlantic Oceans to Hawaii and Norway (NORSAR, see Norwegian Seismic Array) respectively, had been added to the network. From Norway, a terrestrial circuit added an IMP in London to the growing network.
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 wasn't much 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 serial 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 processor product.
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.
The ARPANET and nuclear attacks
A common semi-myth about the ARPANET states that it was designed to be resistant to nuclear attack. The Internet Society 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 networks.
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 wasn't 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 wasn't ARPA's mission to do this; in fact, we'd 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.
Retrospective
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 itself sprung.
References in film and media
In, a character named Sigint takes part in the development of ARPANET after the events depicted in the game.
The Doctor Who Past Doctor Adventures novel Blue Box, written in 2003 but set in 1981, includes a character predicting that by the year 2000 there will be four hundred machines connected to ARPANET.
There is an electronic music artist known as Arpanet. 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 in Japan.
In numerous X Files episodes ARPANET is referenced and usually hacked into by the Lone Gunmen. This is most noticable in the episode Unusual Suspects.Further Information
Get more info on 'Arpanet'.
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