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V.18: New Modem Standard with TTY Capacity


V.18:  the New Standard for Modems with TTY Capacity


The text telephone, known in the deaf community as the TTY, was developed by a deaf physicist in the mid-1960s from existing teletype technology. The TTY network grew in the deaf community because the technology, although old and slow, is dependable and works well in a voice environment. Unfortunately, the TTY uses a code, frequencies, and data transmission speed that are different from those used by computers.

In Europe, text telephony was addressed later than in the U.S. Unlike the U.S., text telephony tended to develop through design and decree by central authorities of the various European countries. As a result, there are several different and incompatible communication protocols used for TTYs in Europe. People who use TTYs do not have the same high level of connectivity that people who use voice communications have: They cannot call text telephones in most other countries.

Dick Brandt, a data communications expert and member of several standards bodies, became interested in these problems when he began consulting with the Technology Assessment Program on how to improve American TTY standards in such a way as to improve interworking between TTYs and computers. Brandt immediately recognized the need for an international specification that could lead to inclusion of TTY protocols in conventional data modems.

Brandt developed an interworking scheme to permit a conventional modem to communicate with several TTY protocols, and this scheme--now standardized as V.18--was studied and ultimately approved by Study Group 14 of the International Telecommunication Union/Telecommunication Standards Bureau (formerly called CCITT).

The development of V.18 was assisted with design specification from Gallaudet's Technology Assessment Program, with input from U.S. TTY manufacturers, and with the assistance of European researchers. The consumer group Telecommunications for the Deaf, Inc. co-sponsored American meetings to discuss V.18 development. Gallaudet's work was sponsored by the U.S. Department of Education/NIDRR through a Rehabilitation Engineering and Research Center on Hearing Enhancement and Assistive Devices.

ITU Recommendation V.18 specifies interworking with the following TTY protocols:

  • Baudot @ 45.45 baud (U.S. TTYs)
  • Baudot @ 50 baud (used in England, Australia, and some other countries; also known as "international" Baudot)
  • V.21/text telephone version (used in Sweden, Norway, and Finland).
  • DTMF (used in Denmark, Holland, and some other countries)
  • EDT ("European Deaf Telephone," used in Germany, Austria, Switzerland, and several other countries)

Implications of V.18

V.18 is the first telecommunication standard that has recognized the technological ghettoization of TTY users. It was a breakthrough to have a standards group address this issue, and a first step toward universal design for accessibility of telecommunication products. It will spawn new products, both in the modem and TTY markets. However, V.18 is not a requirement that all new modems be TTY-compatible. It is a "reference" standard that tells industry how to achieve compatibility. In the U.S., standards are voluntary. We are hopeful, however, that modem manufacturers will want to improve the marketability of their modems, here and in Europe, by making them TTY-compatible.

For example, government purchasers of modems may require V.18, as a way of enhancing compliance with the Americans with Disabilities Act (ADA). Telephone relay services and 911 centers will benefit from V.18 modems. And businesses that are purchasing modems will see V.18 as a way to get a TTY for ADA compliance.

V.18, if implemented in U.S. modems, will first appear in high-end, high-speed modems. Specifically, V.18 would be expected to appear in new V.34 modems. Lower-speed modems, which typically are not the focus of new design and development, probably will not carry V.18.

Modem manufacturers that include V.18 will mark their products as such. This means that a buyer can check a modem's box to determine whether TTY compatibility is built- in.

If V.18 is successful for allowing communication with a wide variety of TTYs, it should generate a new type of TTY (as well as computer modem) that can handle international calls.

It is important to note that V.18 has yet to be tested with real-world products. There probably will be bugs to be ironed out. Gallaudet hopes to take an active role in testing and cooperating with European centers testing V.18.

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