Teletex

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Teletex terminal TTX-11
Terminal adapter for connecting a Teletex terminal to ISDN

The Teletex service was an internationally standardized text communication service for the transmission of texts at a speed of up to 2400 bit / s.

Teletex was offered in Germany from 1981 to 1993, and Datex-L , Datex-P and ISDN were used as the transmission network .

The teletex service was a further development of the telex or telex service and was largely compatible with it.

Instead of the 5-bit telex character set , which recognizes no difference between uppercase and lowercase letters, a character set consisting of 332 characters, represented in 8 bits, was used, with which all languages ​​used in Europe can be spelled correctly, which at the time of its introduction (1981 ) used the Latin writing system. This character set was standardized by the ISO as ISO 6937 , by the CCITT as the ITU as CCITT T.61 .

history

Teletex (abbreviation: Ttx) was to generally replace the telex service, which was no longer fast at around 50 bit / s. Teletex terminals were a combination of electronic telex and typewriter in one device. In Germany, the service was introduced by the Deutsche Bundespost in 1981 and stopped again in 1993. At the beginning of 1986 there were around 12,600 Teletex subscribers in the Federal Republic of Germany. With a Teletex-Telex converter (TTU) the service transition for the transmission of messages between Teletex and Telex connections was possible. This means that messages could be sent from a telex machine or teletype to a teletex machine and vice versa.

The Teletex service has not caught on in the market for several reasons:

  • Although the advertising promised an office machine, you could only write in portrait mode and not create tables.
  • When using text attributes, the full line length could not be used. How much was to be deducted was not stated anywhere.
  • The combined characters were made using the type "." created. As a result, the typeface was inconsistent. After a while the type broke off.
  • The typewriters specializing in teletex were expensive. Instead of these devices, PCs are becoming increasingly popular . However, these PCs or intermediate receiving boxes had to meet high requirements, e.g. B. be accessible day and night, which also made this variant expensive.
  • Fax machines made it possible to transmit any message as an image. This removed the restrictions of the character set . Existing items could be sent (including forms and brochures) and nothing had to be typed. The devices were affordable, fax traffic became the standard in business and was also used by those who would never have bought a teleprinter.
  • From the end of the 1980s, e-mail began its triumphal march as a means of communication, initially hesitantly, but in widespread use from the early 1990s. It meant significantly lower costs and equipment costs compared to Teletex as well as a rapidly increasing range of functions such as file attachments even up to sound and video (the Commodore Amiga had been on sale as a "multimedia computer" since 1986), which Teletex could not offer.

Teletex terminals

The most widely used Teletex terminal in Germany was the T4200 from Siemens AG with several thousand units . The device combined the functions of a normal typewriter, a memory typewriter with removable storage and screen, a teletex terminal and a teleprinter.

The company Commodore also brought out a Teletex-capable system in Germany consisting of a Commodore computer , a connection box with a built-in control computer, a specially expanded word processor and an adapted type wheel printer CBM 8229 . Sales did not even reach 20 and the project was soon discontinued.

The Olivetti ET 351 TTX was a word processing machine based on a type wheel typewriter of the first generation of the Olivetti ET series with two 5.25-inch floppy disk drives . One started the machine's proprietary operating system and could be used to save word processing documents, the other was reserved for teletex reception and not accessible to the user. In contrast to the normal version , the ET 351 , the ET 351 TTX was mostly equipped with a continuous printing paper tractor. This machine had a starting price of over 14,000 DM in 1982, which was about the purchase price of a mid-range car. The basic fee was 200 DM, plus transmission costs. Since the device was not allowed to be switched off, it heated the room like three people.

Teletex terminals are standardized in the CCITT recommendation T.60.

Differences Between Teletex and Telex Service

The conception of the Teletex service provided for the following performance features:

  • Instead of the Telex character set ( Baudot code ), a Teletex character set was defined that could correctly display texts in practically all European languages. Unlike in the family of 8-bit character sets defined in ISO 8859 , which provide a different coding for each group of languages, the Teletex character set T.61 provides a total of 14 combining characters that do not advance the writing position the following characters are combined with this diacritical mark. A total of 332 characters can be displayed.
  • Teletex-capable typewriters could have mostly single-line text displays or a screen , editing options and intermediate storage and could automatically send the Teletex messages at definable times. They could get the form of a typewritten letter, which was not possible with the telex service.
  • Teletex terminals such as the Olivetti ET 351 TTX also carried out a text conversion between currency symbols that cannot be printed for telex terminals into their abbreviations consisting of letters, e.g. B. "$" to "USD" or "£" to "GBP".
  • The teletex messages were sent at a much higher transmission rate than the telex messages . Teletex devices could send and receive each other at a speed of 2400 bit / s. This corresponded to the transfer of a DIN A4 page in approx. 10 seconds.
  • The error rate was 10 times better than the telex service.

literature