| A telecommunications device for the deaf | | | | |
| (TDD) is an electronic device for text | | | | Micon produced over 1,000 MCMs per month |
| communication via a telephone line, used when | | | | resulting in approximately 50,000 MCMs being |
| one or more of the parties has hearing or | | | | disseminated into the deaf community. Before |
| speech difficulties. Other names for TDD | | | | he left Micon in 1980, Michael Cannon |
| include TTY (telephone typewriter or | | | | developed several computer compatible |
| teletypewriter), textphone (Common in Europe) | | | | variations of the MCM and a portable, battery |
| and minicom (United Kingdom). | | | | operated printing TDD, but they were never as |
| | | | popular as the original MCM. Newer model TDDs |
| About The typical TDD is a device about the | | | | could communicate with selectable codes that |
| size of a small laptop computer with a QWERTY | | | | allow communications at a higher bit rate on |
| keyboard and small screen that uses | | | | those models similarly equipped. |
| light-emitting diodes or an LCD screen to | | | | |
| display typed text electronically. In | | | | However, the lack of true computer interface |
| addition, TDDs commonly have a small spool of | | | | functionality spelled the demise of the |
| paper on which text is also printed — | | | | original TTY and its clones. During the |
| old versions of the device had only a printer | | | | mid-1970s other so-called portable telephone |
| and no screen. The text is transmitted live, | | | | devices were being cloned by other companies, |
| via a telephone line, to a compatible device, | | | | and this was the time period when the term |
| i.e. one that uses a similar communication | | | | "TDD" began being used largely by those |
| protocol. In certain countries there are | | | | outside the deaf community. The deaf |
| Telecommunications Relay Services, so that a | | | | community, interestingly, does not usually |
| deaf person can communicate with a hearing | | | | use the term "TDD" but instead prefers "TTY." |
| person on an ordinary voice phone using a | | | | Protocols There are many different textphone |
| human relay operator. There are also | | | | standards. The original standard used by TDDs |
| "carry-over" services, enabling people who | | | | is the Baudot code implemented asynchronously |
| can hear but cannot speak ("hearing | | | | at either 45.5 or 50 baud, 1 start bit, 5 |
| carry-over"), or people who cannot hear but | | | | data bits, and 1.5 stop bits. Baudot is a |
| are able to speak ("voice carry-over") to use | | | | common protocol in the US. In Europe, |
| the telephone. | | | | different states use different protocols. For |
| | | | example, V.21 is found in the UK and several |
| History APCOM (Applied Communications) | | | | Scandinavian countries. Other protocols used |
| located in the San Francisco Bay area | | | | for text telephony are EDT, DTMF, V.23, etc. |
| developed the acoustic coupler, or modem. | | | | |
| Couplers were cabled to TTYs enabling the | | | | The TDD/TTY protocols are generally |
| Bell Telephone company standard "500 handset" | | | | incompatible with standard Hayes-compatible |
| to couple, or fit, into the rubber cups on | | | | modems. In 1994 the ITU approved the V.18 |
| the coupler, thus transmitting and receiving | | | | standard. V.18 is a dual standard. It is both |
| a unique set of tones generated by the | | | | an umbrella protocol that allows recognition |
| different corresponding TTY keys. | | | | and interoperability of some of the most |
| | | | commonly used textphone protocols, as well as |
| The entire configuration of teletype machine, | | | | offering a native V.18 mode, which is an |
| acoustic coupler, and telephone set became | | | | ASCII full- or half-duplex modulation method. |
| known as the TTY. The acoustic coupler modem | | | | |
| was the invention of deaf physicist Robert | | | | Computers can, with appropriate software and |
| Weitbrecht in 1964. The actual mechanism for | | | | modem, emulate a V.18 TDD. Some voice modems, |
| TTY communications was accomplished | | | | coupled with appropriate software, can now be |
| electromechanically through frequency shift | | | | converted to TDD modems by using a |
| keying (FSK) allowing only one-way (simplex) | | | | software-based decoder for TDD tones. |
| communication. In 1973 the MCM (Manual | | | | |
| Communications Module), which was the world's | | | | In the UK, a virtual V.18 network, called |
| first electronic portable TDD (Telephone | | | | TextDirect, exists as part of the Public |
| Device for the Deaf) allowing two-way | | | | Switched Telephone Network, thereby offering |
| telecommunications, premiered at the CAD | | | | interoperability between textphones using |
| (California Association of the Deaf) | | | | different protocols. |
| convention in Sacramento, California. | | | | |
| | | | The platform also offers additional |
| Enlarge The battery-powered MCM was invented | | | | functionality like call progress and status |
| and designed by Michael Cannon in conjunction | | | | information in text and automatic invocation |
| with physicist Art Ogawa and deaf interpreter | | | | of a relay service for speech-to-text calls. |
| Kit Patrick Corson. It was manufactured by | | | | |
| Michael Cannon's company, Micon Industries, | | | | In addition to regular Baudot, the UltraTec |
| and initially marketed by Kit Corson's | | | | company implements another protocol known as |
| company, Silent Communications. In order to | | | | Enhanced TTY, which it calls "Turbo Code," in |
| be compatible with the existing TTY network, | | | | its products. |
| the MCM was designed around the five-bit | | | | |
| Baudot code established by the older TTY | | | | Turbo Code has some advantages over Baudot |
| machines instead of the ASCII code used by | | | | protocols, such as a higher data rate, full |
| computers. The MCM was an instant success | | | | ASCII compliance, and full-duplex capability. |
| with the deaf community despite the drawback | | | | However, Turbo Code is proprietary, and |
| of a $599 cost. Within six months there were | | | | UltraTec only gives its specifications to |
| more MCMs in use by the deaf and hearing | | | | parties who are willing to license it. |
| impaired than TTY machines. After a year | | | | |
| Micon took over the marketing of the MCM and | | | | Devices In addition to TDD, there are a |
| subsequently concluded a deal with Pacific | | | | number of pieces of additional equipment that |
| Bell (who coined the term "TDD") to purchase | | | | can be coupled to telephones to improve their |
| MCMs and rent them to deaf telephone | | | | utility. For those with hearing difficulties |
| subscribers for $30 per month. After Micon | | | | the telephone ring and conversation sound |
| formed an alliance with APCOM, Michael | | | | level can be amplified or pitch adjusted, |
| Cannon, Paul Conover (Micon), and Andrea Saks | | | | ambient noise can also be filtered. The |
| (APCOM) successfully petitioned the | | | | amplifier can be a simple addition or through |
| California Public Utilities Commission (CPUC) | | | | an inductive coupler to interact with |
| resulting in a tariff that paid for TDD | | | | suitable hearing aids. The ring can also be |
| devices to be distributed free of cost to | | | | supplemented with extension bells or a visual |
| deaf persons. | | | | call indicator. |