Writing phone
A writing telephone (often referred to as a Telescrit in Switzerland ) is a telecommunications device that only transmits and receives characters or text instead of spoken sounds . It is used for telecommunication for deaf and hard of hearing people.
In contrast to the teleprinter , the typeface is structurally smaller and not intended for paper printouts in the standard format. Functionally, it is an isolated solution , as there is no compatibility with other telecommunications terminals.
history
In 1964, the deaf orthodontist James C. Marsters sent from Pasadena , California , the deaf physicist Robert Weitbrecht in Redwood City , California, to a teletype. Weitbrecht realized that the device was suitable for telecommunications for deaf people. He constructed a modem with which the teletype could be operated on the telephone network. This created the first writing telephone, albeit in a bulky and expensive form.
The first German writing telephone, developed in 1975 by Michael Krause from Münster , had a letter keypad and a metal-coated paper strip onto which the consecutive letters of the message text were burned. Newer models have multi-line LC - screens on which the written and received text to appear.
Due to newer technologies, the writing telephone is now considered out of date; its importance is steadily declining, as its purpose is also fulfilled with services and devices such as instant messaging , SMS , fax machines , e-mail and also with images using videophones and webcams .
Technical
The signals were usually transmitted through an acoustic coupler , newer models also offered a direct connection to the telephone line parallel to the acoustic coupler. The acoustic coupler was included in many devices so that they could be taken with you on trips (e.g. in hotels).
Transmission protocols
The writing telephones were rarely cross-border compatible .
The first write telephones in the USA used the Baudot code for transmission , later the ASCII code. In the German-speaking countries, on the other hand, the EDT protocol ( European Deaf Telephone ) was used. In the Netherlands and Denmark, on the other hand, multi-frequency dialing was used , with one letter corresponding to two keys (consisting of 0–9, * and #). The transmitted tones were coded or decoded by special devices with the help of a QWERTY keyboard and displayed on a screen.
In France, the online service Minitel, which is widespread there, was often used with the associated devices for text communication, while in Sweden, Norway and Finland communication was again via the V.21 protocol. As a result, many users turned to personal computers and modems for this. The advantage was that the call participants did not need a precisely defined device type. The disadvantage, however, was that both subscriber devices had to be connected to the network and ready for operation at an agreed time for a functioning connection. In principle, spontaneous phone calls were not possible.
European Deaf Telephone (EDT)
In the German-speaking countries, Italy, Spain and Malta, the proprietary EDT protocol ( European Deaf Telephone ) was used, which is based on the ITU V.21 protocol ( frequency shift keying ).
EDT is operated at 110 baud , half duplex . A 7-bit character set, the ITU-T.50 code, was used for character transmission. Many devices use the NAK command (Code 21) for the backspace function, which moves the cursor or the current processing position back one position and deletes the character located there. This proprietary protocol had the disadvantage that it was not possible to communicate with computer modems, due to the implementation of additional protocols in the later models of writing phones, e.g. B. that of the manufacturer ghe-ces Wald, this could be avoided.
harmonization
Harmonization was sought in the 1990s, and in 1994 the International Telecommunication Union (ITU) issued a recommendation ( ITU V.18). ITU V.18 ensures downward compatibility with the common written telephone protocols such as EDT, but in view of newer technologies with text transmission in telecommunications, corresponding devices have hardly been produced.
function
As in a normal telephone conversation, the caller dials the number of the respective interlocutor and places the telephone receiver in the recess provided for this purpose in the writing telephone. Now he waits for the answer from the called party. The conversation is similar to instant messaging , with the difference that you can "interrupt" the conversation partner and text entry and transmission are "live". To signal to your counterpart that you have finished your speech, you type certain special characters. Depending on the device, these are ** or ## .
Sample conversation
(The interlocutors use different devices)
HALLO HIER (Name) **
HALLO HIER (Name), WANN WIRST DU HEUTE ABEND HIER SEIN? ##
ICH DENKE MAL SO GEGEN ACHT. **
ALLES KLAR, BIS DANN. ## TSCHUESS ** ## ##
See also
Web links
Individual evidence
- ↑ a b c Telecommunications Industry Association: Baseline and Enhancements for handling text conversations in an IP network, TR30.1 / 03-02-004.
- ↑ a b c d Zagler, Wolfgang. 2012: Communication technology for disabled and old people (PDF; 10.4 MB). Center for Applied Assistive Technologies, Institute for Design and Impact Research, TU Vienna.
- ↑ a b ITU: V.18 Operational and interworking requirements for DCEs operating in the text telephone mode (11/2000) Online .
- ^ A b Commission of the European communities, 1991: COST 220. If I call, who can answer? Text telephone system in use in Europe - A way forward to compatibility.
- ↑ Telescrit 2002/2108 writing telephone with direct connection to the telephone network PDF