The telex network was a public switched network of teleprinters
similar to a telephone network, for the purposes of sending text-based
Telex was a major method of sending written messages
electronically between businesses in the post World War II period. Its
usage went into decline as the fax machine grew in popularity in the
The "telex" term refers to the network, not the teleprinters;
point-to-point teleprinter systems had been in use long before telex
exchanges were built in the 1930s. Teleprinters evolved from telegraph
systems, and, like the telegraph, they used binary signals, which
means that symbols were represented by the presence or absence of a
pre-defined level of electric current. This is significantly different
from the analog telephone system, which used varying voltages to
encode frequency information. For this reason, telex exchanges were
entirely separate from the telephone system, with their own signalling
standards, exchanges and system of "telex numbers" (the counterpart of
Telex provided the first common medium for international record
communications using standard signalling techniques and operating
criteria as specified by the International
Customers on any telex exchange could deliver messages to any other,
around the world. To lower line usage, telex messages were normally
first encoded onto paper tape and then read into the line as quickly
as possible. The system normally delivered information at 50 baud or
approximately 66 words per minute, encoded using the International
Telegraph Alphabet No. 2. In the last days of the telex networks,
end-user equipment was often replaced by modems and phone lines,
reducing the telex network to what was effectively a directory service
running on the phone network.
2 Operation and applications
3 United States
3.1 Teletypewriter Exchange Service (TWX)
3.2 Western Union
3.3 International Record Carriers
4 United Kingdom
7 See also
9 Further reading
British Telecom "Puma" telex machine of the 1980s
Telex began in Germany as a research and development program in 1926
that became an operational teleprinter service in 1933. The service,
operated by the
Reich postal service) had a speed of 50
baud — approximately 66 words per minute.
Telex service spread within Europe and (particularly after 1945)
around the world. By 1978, West Germany, including West Berlin, had
123,298 telex connections. Long before automatic telephony became
available, most countries, even in central
Africa and Asia, had at
least a few high-frequency (shortwave) telex links. Often, government
postal and telegraph services (PTTs) initiated these radio links. The
most common radio standard, CCITT R.44 had error-corrected
retransmitting time-division multiplexing of radio channels. Most
impoverished PTTs operated their telex-on-radio (TOR) channels
non-stop, to get the maximum value from them.
The cost of TOR equipment has continued to fall. Although the system
initially required specialised equipment, as of 2016[update] many
amateur radio operators operate TOR (also known as RTTY) with special
software and inexpensive hardware to adapt computer sound cards to
Modern cablegrams or telegrams actually operate over dedicated telex
networks, using TOR whenever required.
Telex served as the forerunner of modern fax, email, and text
messaging — both technically and stylistically. Abbreviated English
(like "CU L8R" for "see you later") as used in texting originated with
telex operators exchanging informal messages in real time[citation
needed] — they became the first "texters" long before the
introduction of mobile phones.
Telex users could send
the same message to several places around the world at the same time,
like email today, using the
Western Union InfoMaster Computer. This
involved transmitting the message via paper tape to the InfoMaster
Computer (dial code 6111) and specifying the destination addresses for
the single text. In this way, a single message could be sent to
Telex and TWX machines as well as delivering the same
message to non-
Telex and non-TWX subscribers via Western Union
Operation and applications
Telex messages are routed by addressing them to a telex address, e.g.,
"14910 ERIC S", where 14910 is the subscriber number, ERIC is an
abbreviation for the subscriber's name (in this case
Telefonaktiebolaget L.M. Ericsson in Sweden) and S is the country
code. Solutions also exist for the automatic routing of messages to
different telex terminals within a subscriber organization, by using
different terminal identities, e.g., "+T148".
A major advantage of telex is that the receipt of the message by the
recipient could be confirmed with a high degree of certainty by the
"answerback". At the beginning of the message, the sender would
transmit a WRU (Who aRe yoU) code, and the recipient machine would
automatically initiate a response which was usually encoded in a
rotating drum with pegs, much like a music box. The position of the
pegs sent an unambiguous identifying code to the sender, so the sender
could verify connection to the correct recipient. The WRU code would
also be sent at the end of the message, so a correct response would
confirm that the connection had remained unbroken during the message
transmission. This gave telex a major advantage over group 2 fax which
had no inherent error-checking capability.
The usual method of operation was that the message would be prepared
off-line, using paper tape. All common telex machines incorporated a
5-hole paper-tape punch and reader. Once the paper tape had been
prepared, the message could be transmitted in minimum time. Telex
billing was always by connected duration, so minimizing the connected
time saved money. However, it was also possible to connect in "real
time", where the sender and the recipient could both type on the
keyboard and these characters would be immediately printed on the
Telex could also be used as a rudimentary but functional carrier of
information from one IT system to another, in effect a primitive
forerunner of Electronic Data Interchange. The sending IT system would
create an output (e.g., an inventory list) on paper tape using a
mutually agreed format. The tape would be sent by telex and collected
on a corresponding paper tape by the receiver and this tape could then
be read into the receiving IT system.
One use of telex circuits, in use until the widescale adoption of
Internet email, was to facilitate a message handling system,
allowing local email systems to exchange messages with other email and
telex systems via a central routing operation, or switch. One of the
largest such switches was operated by
Royal Dutch Shell
Royal Dutch Shell as recently as
1994, permitting the exchange of messages between a number of IBM
Digital Equipment Corporation
Digital Equipment Corporation
ALL-IN-1 and Microsoft
Mail systems. In addition to permitting email to be sent to telex,
formal coding conventions adopted in the composition of telex messages
enabled automatic routing of telexes to email recipients.
Teletypewriter Exchange Service (TWX)
The Teletypewriter Exchange Service (TWX) was developed by the
AT&T Corporation in the United States. It originally transmitted
at 45.45 baud or approximately 60 words per minute, using five level
Baudot code. AT&T began TWX on November 21, 1931. AT&T
later[when?] developed a second generation of TWX called "four row"
that used the 110 baud, using eight level
ASCII code. TWX was offered
in both "3-row" Baudot and "4-row"
ASCII versions up to the late
TWX used the public switched telephone network. In addition to having
separate area codes (510, 610, 710, 810 and 910) for the TWX service,
the TWX lines were also set up with a special Class of Service to
prevent connections from POTS to TWX and vice versa.
The code/speed conversion between "3-row" Baudot and "4-row"
service was accomplished using a special Bell "10A/B board" via a live
operator. A TWX customer would place a call to the 10A/B board
operator for Baudot –
ASCII – Baudot calls and also
TWX Conference calls. The code / speed conversion was done by a
Western Electric unit that provided this capability. There were
multiple code / speed conversion units at each operator position.
AT&T published the trade magazine TWX, related to the
Teletypewriter Exchange Service from 1944 to 1952. It published
articles that touched upon many aspects of the technology.
Western Union purchased the TWX system from AT&T in January
1969. The TWX system and the special US area codes (510, 710, 810
and 910) continued until 1981, when
Western Union completed the
conversion to the
Telex II system. Any remaining "3-row"
Baudot customers were converted to
Telex service during
the period 1979 to 1981.
Bell Canada retained area code 610 until
1992; its remaining numbers were moved to non-geographic area code
The modem for this service was the
Bell 101 dataset, which is the
direct ancestor of the
Bell 103 modem that launched computer
time-sharing. The 101 was revolutionary because it ran on ordinary
unconditioned telephone subscriber lines, allowing the Bell System to
run TWX along with POTS on a single public switched telephone network.
Telex II was the name for the TWX network after it was acquired from
AT&T by Western Union. It was re-acquired by AT&T in 1990 in
the purchase of the
Western Union assets that became AT&T EasyLink
Western Union started to build a telex network in the United
States. This telex network started as a satellite exchange located
in New York City and expanded to a nationwide network. Western Union
chose Siemens & Halske AG, now Siemens AG, and ITT to supply
the exchange equipment, provisioned the exchange trunks via the
Western Union national microwave system and leased the exchange to
customer site facilities from the local telephone company. Teleprinter
equipment was originally provided by Siemens & Halske AG and
later by Teletype Corporation. Initial direct international telex
service was offered by Western Union, via W.U. International, in the
summer of 1960 with limited service to London and Paris. In 1962,
the major exchanges were located in New York City (1), Chicago (2),
San Francisco (3), Kansas City (4) and Atlanta (5). The telex
network expanded by adding the final parent exchanges cities of Los
Angeles (6), Dallas (7), Philadelphia (8) and Boston (9) starting in
The telex numbering plan, usually a six-digit number in the United
States, was based on the major exchange where the customer's telex
machine terminated. For example, all telex customers that
terminated in the New York City exchange were assigned a telex number
that started with a first digit "1". Further, all Chicago-based
customers had telex numbers that started with a first digit of "2".
This numbering plan was maintained by
Western Union as the telex
exchanges proliferated to smaller cities in the United States. The
Telex network was built on three levels of
exchanges. The highest level was made up of the nine exchange
cities previously mentioned. Each of these cities had the dual
capability of terminating telex customer lines and setting up trunk
connections to multiple distant telex exchanges. The second level of
exchanges, located in large cities such as Buffalo, Cleveland, Miami,
Newark, Pittsburgh and Seattle, were similar to the highest level of
exchanges in capability of terminating telex customer lines and
setting up trunk connections. However, these second level exchanges
had a smaller customer line capacity and only had trunk circuits
connected to regional cities. The third level of exchanges, located in
small to medium-sized cities, could terminate telex customer lines and
had a single trunk group running to its parent exchange.
Loop signaling was offered in two different configurations for Western
Telex in the United States. The first option, sometimes called
local or loop service, provided a 60 milliampere loop circuit from the
exchange to the customer teleprinter. The second option, sometimes
called long distance or polar was used when a 60 milliampere
connection could not be achieved, provided a ground return polar
circuit using 35 milliamperes on separate send and receive wires. By
the 1970s, under pressure from the Bell operating companies wanting to
modernize their cable plant and lower the adjacent circuit noise that
these telex circuits sometimes caused,
Western Union migrated
customers to a third option called F1F2. This F1F2 option replaced the
DC voltage of the local and long distance options with modems at the
exchange and subscriber ends of the telex circuit.
Western Union offered connections from
Telex to the AT&T
Teletypewriter eXchange (TWX) system in May 1966 via its New York
Information Services Computer Center. These connections were
limited to those TWX machines that were equipped with automatic
answerback capability per CCITT standard.
Telex users could send the same message to several places
around the world at the same time, like email today, using the Western
Union InfoMaster Computer. This involved transmitting the message via
paper tape to the InfoMaster Computer (dial code 6111) and specifying
the destination addresses for the single text. In this way, a single
message could be sent to multiple distant
Telex and TWX machines as
well as delivering the same message to non-
Telex and non-TWX
Western Union Mailgram.
International Record Carriers
"International Record Carrier" (IRC) was a term created by the Federal
Communications Commission (FCC) in the United States. Bell's original
consent agreement limited it to international dial telephony, and the
Telegraph Company had given up its international
telegraphic operation in a 1939 bid to monopolize U.S. telegraphy by
taking over ITT's
Postal, telegraph and telephone service (PTT)
business. The result was a de-emphasis on telex in the U.S. and the
creation of several international telex and telegraphy companies,
collectively called IRCs:
Telegraph Company developed a subsidiary named Western
Union Cable System. This company was later renamed as Western Union
International (WUI) when it was spun off by
Western Union as an
independent company. WUI was purchased by
MCI Communications (MCI) in
1983 and operated as a subsidiary of MCI International.
ITT's "World Communications" division (later known as ITT World
Communications) was amalgamated from many smaller companies: Federal
Telegraph, All American Cables and Radio, Globe Wireless, and the
common carrier division of Mackay Marine. ITT World Communications was
Western Union in 1987.
RCA Communications (later known as
RCA Global Communications) had
specialized in global radiotelegraphic connections. In 1986, it was
purchased by MCI International.
Before World War I, the Tropical Radiotelegraph Company (later known
as Tropical Radio Telecommunications, or TRT) put radio telegraphs on
ships for its owner, the
United Fruit Company
United Fruit Company (UFC), to enable them to
deliver bananas to the best-paying markets. Communications expanded to
UFC's plantations, and were eventually provided to local governments.
TRT eventually became the national carrier for many small Central
Telegraph Cable Company (later known as FTC Communications,
or just FTCC), which was founded in 1871, was owned by French
investors and headquartered in the United States; it laid
transatlantic cable between the two countries. International telegrams
routed via FTCC used routing ID "PQ", the initials of the company's
Augustin Pouyer-Quertier (1820–1891).
Firestone Rubber developed its own IRC, the Trans-Liberia
Radiotelegraph Company, which operated shortwave from
Akron, Ohio to the rubber plantations in Liberia.
Telex users had to select which IRC to use, and then append the
necessary routing digits. The IRCs converted between TWX and Western
Telegraph Co. standards.
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Telex began in the UK as an evolution from the 1930s
service, appearing in 1932 on a limited basis. This used the telephone
network in conjunction with a
Teleprinter 7B and signalling equipment
to send a message to another subscriber with a Teleprinter, or to the
In 1945 as the traffic increased it was decided to have a separate
Telex traffic and the first manual exchange opened in
London. By 1954, the public inland
Telex service opened via manually
switched exchanges. A number of subscribers were served via automatic
sub-centres which used relays and Type 2 uniselectors, acting as
concentrators for a manual exchange.
In the late 1950s the decision was made to convert to automatic
switching and this was completed by 1961; there were 21 exchanges
spread across the country, with one international exchange in London.
The equipment used the Strowger system for switching, as was the case
for the telephone network. Conversion to Stored Programme Control
(SPC) began in 1984 using exchanges made by Canadian Marconi, with the
last Strowger exchange closing in 1992. User numbers increased over
the following years into the 1990s.
The dominant supplier of the
Telex machines was Creed, a division of
A separate service "Secure Stream 300" (previously Circuit Switched
Data Network) was a variant of
Telex running at 300 baud, used for
telemetry and monitoring purposes by utility companies and banks,
among others. This was a high security virtual private wire system
with a high degree of resilience through diversely routed dual-path
British Telecom stopped offering the
Telex service to new customers in
2004 and discontinued the service in 2008, allowing users to transfer
Telex if they wished to continue to use Telex.
Canada-wide automatic teleprinter exchange service was introduced by
Telegraph Company and CN
Telegraph in July 1957 (the two
companies, operated by rivals
Canadian National Railway
Canadian National Railway and Canadian
Pacific Railway, would join to form
CNCP Telecommunications in 1967).
This service supplemented the existing international telex service
that was put in place in November 1956. Canadian telex customers could
connect with nineteen European countries in addition to eighteen Latin
American, African, and trans-Pacific countries. The major
exchanges were located in
Toronto (02), and Winnipeg
Telex is still in operation but not in the sense described in the
CCITT Blue Book documentation. iTelegram offers "telex" without
subscriber telex lines. Individual subscribers can use Deskmail, a
legacy Windows program that connects to the iTelegram telex network
but this is via IP as the "last mile".,
Telex has been mostly
superseded by fax, email, and SWIFT, although radiotelex, telex via HF
radio, is still used in the maritime industry and is a required
element of the Global Maritime Distress and Safety System.
Telegraphy § 21st-century decline for current status in
Dot matrix printing
^ "Fifty years of telex".
Telecommunication Journal. International
Telecommunication Union. 51: 35. 1984. Retrieved 2017-05-18. Just over
fifty years ago, in October 1933, the Deutsche
Reichspost as it was
then known, opened the world's first public teleprinter network.
^ Roemisch, Rudolf (1978). "Siemens EDS System in Service in Europe
and Overseas". Siemens Review. Siemens-Schuckertwerke AG. 45 (4): 176.
Retrieved 2016-02-04. The inauguration of the first telex service in
the world in Germany in 1933 was soon followed by the development of
similar networks in several more European countries. However, telex
did not enjoy significant and worldwide growth until after 1945.
Thanks to the great advantages of the new telex service, above all in
overcoming time differences and language problems, telex networks were
introduced in quick succession in all parts of the world.
^ "RTTY Software". The DXZone.
^ Anton A. Huurdeman (2003). The worldwide history of
telecommunications. Wiley. p. 302.
^ "Typing From Afar" (PDF).
^ "WU to Buy AT&T TWX".
Western Union News. II (4). January 15,
^ Easterlin, Phillip R. (April 1959). "
Telex in New York". Western
Union Technical Review: 45. ISSN 0096-6452.
^ Easterlin, Phillip R. (October 1960). "
Telex in Private Wire
Western Union Technical Review: 131.
^ Chin, James S.; Gomerman, Jan J. (July 1966). "CSR4 Exchange".
Western Union Technical Review: 142–9.
^ Smith, Fred W. (October 1960). "European Teleprinters". Western
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^ Smith, Fred W. (January 1964). "A New Line of Light-duty
Teleprinters and ASR Sets".
Western Union Technical Review:
^ O’Sullivan, T.J. (July 1963). "TW 56 Concentrator". Western Union
Technical Review: 111–2.
^ Easterlin, Phillip R. (January 1962). "
Telex in the U.S.A.". Western
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^ Jockers, Kenneth M. (July 1966). "Planning
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Western Union Technical Review: 92–95.
^ Jockers, Kenneth M. (July 1966). "Planning
Western Union Telex".
Western Union Technical Review: 94 figure 2.
^ Wernikoff, Sergio (July 1966). "Information Services Computer
Western Union Technical Review: 130.
^ Colombo, C.J. (January 1958). "
Telex in Canada". Western Union
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^ Easterlin, Phillip R. (April 1959). "
Telex in New York". Western
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^ "International Telegram® - Answers to some common questions".
itelegram.com. 2017. Retrieved 2017-05-18.
Western Union closed its
telegram service in January, 2006.
Western Union is now the fastest
way to send money online, and iTelegram is the fastest way to send
telegram messages. Western Union's telex/cablegram network, Mailgram®
service, and Deskmail/Infomaster services are now a part of
^ "International Telegram - Send a telegram to Antarctica".
itelegram.com. 2017. Retrieved 2017-05-18. Delivery: Service by telex
/ fax / e-mail or INMARSAT terminal (sender must provide number or
Pitts, M. K. (May 1950). "International Communications Facilities of
the American Carriers".
RCA Communications, Inc.
Cable protection system
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Timeline of communication technology
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Edwin Howard Armstrong
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Alexander Graham Bell
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