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Text telephones guide

A telecommunications device for the deaf
(TDD) is an electronic device for textMicon produced over 1,000 MCMs per month
communication via a telephone line, used whenresulting in approximately 50,000 MCMs being
one or more of the parties has hearing ordisseminated into the deaf community. Before
speech difficulties. Other names for TDDhe left Micon in 1980, Michael Cannon
include TTY (telephone typewriter ordeveloped 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 thecould communicate with selectable codes that
size of a small laptop computer with a QWERTYallow communications at a higher bit rate on
keyboard and small screen that usesthose  models  similarly  equipped.
light-emitting diodes or an LCD screen to
display typed text electronically. InHowever, the lack of true computer interface
addition, TDDs commonly have a small spool offunctionality 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 printermid-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 areoutside the deaf community. The deaf
Telecommunications Relay Services, so that acommunity, interestingly, does not usually
deaf person can communicate with a hearinguse the term "TDD" but instead prefers "TTY."
person on an ordinary voice phone using aProtocols There are many different textphone
human relay operator. There are alsostandards. The original standard used by TDDs
"carry-over" services, enabling people whois the Baudot code implemented asynchronously
can hear but cannot speak ("hearingat either 45.5 or 50 baud, 1 start bit, 5
carry-over"), or people who cannot hear butdata bits, and 1.5 stop bits. Baudot is a
are able to speak ("voice carry-over") to usecommon 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 areafor  text telephony are EDT, DTMF, V.23, etc.
developed the acoustic coupler, or modem.
Couplers were cabled to TTYs enabling theThe TDD/TTY protocols are generally
Bell Telephone company standard "500 handset"incompatible with standard Hayes-compatible
to couple, or fit, into the rubber cups onmodems. In 1994 the ITU approved the V.18
the coupler, thus transmitting and receivingstandard. V.18 is a dual standard. It is both
a unique set of tones generated by thean 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 becameASCII full- or half-duplex modulation method.
known as the TTY. The acoustic coupler modem
was the invention of deaf physicist RobertComputers can, with appropriate software and
Weitbrecht in 1964. The actual mechanism formodem, emulate a V.18 TDD. Some voice modems,
TTY communications was accomplishedcoupled with appropriate software, can now be
electromechanically through frequency shiftconverted 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'sIn the UK, a virtual V.18 network, called
first electronic portable TDD (TelephoneTextDirect, exists as part of the Public
Device for the Deaf) allowing two-waySwitched Telephone Network, thereby offering
telecommunications, premiered at the CADinteroperability 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 inventedfunctionality like call progress and status
and designed by Michael Cannon in conjunctioninformation in text and automatic invocation
with physicist Art Ogawa and deaf interpreterof  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'scompany implements another protocol known as
company, Silent Communications. In order toEnhanced 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 TTYTurbo Code has some advantages over Baudot
machines instead of the ASCII code used byprotocols, such as a higher data rate, full
computers. The MCM was an instant successASCII compliance, and full-duplex capability.
with the deaf community despite the drawbackHowever, Turbo Code is proprietary, and
of a $599 cost. Within six months there wereUltraTec only gives its specifications to
more MCMs in use by the deaf and hearingparties  who  are  willing  to  license  it.
impaired than TTY machines. After a year
Micon took over the marketing of the MCM andDevices In addition to TDD, there are a
subsequently concluded a deal with Pacificnumber of pieces of additional equipment that
Bell (who coined the term "TDD") to purchasecan be coupled to telephones to improve their
MCMs and rent them to deaf telephoneutility. For those with hearing difficulties
subscribers for $30 per month. After Miconthe telephone ring and conversation sound
formed an alliance with APCOM, Michaellevel can be amplified or pitch adjusted,
Cannon, Paul Conover (Micon), and Andrea Saksambient noise can also be filtered. The
(APCOM) successfully petitioned theamplifier 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 TDDsuitable hearing aids. The ring can also be
devices to be distributed free of cost tosupplemented with extension bells or a visual
deaf  persons.call indicator.



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