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