TDD

Guest Post: The Deaf Use the Phone?

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UPDATED: March 29, 2016 Title has been renamed to reflect the original submission.

I received a submission of a guest post from Jason from Montana, edited by your humble curator kinda out of the blue. I did a pretty brief post on TTY a couple weekends ago and was surprised that I’d get a response, and got more insight to the TDD use of TTY. I’ve been meaning to post this subject for a while. Anyways the rest of the post is from him.

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Yup, it’s true, the deaf can use the phone. And ironically, they’ve been able to for many years.  The Telecommunications Act of 1982 “allows states to require carriers to continue providing subsidies for specialized equipment needed by persons with impaired hearing, speech, vision, or mobility”.

 The TTY device introduced in the 1970’s used the Baudot protocol to transmit text over standard telephone lines.  They’re actually primitive modems in the sense that TTY’s use Frequency Shift Keying to have a tone match the character typed on the keyboard.  Baudot runs very slow by comparison at only 50 baud.  Most TTY’s have a character buffer so one can type faster than 50 baud, and the TTY will transmit as fast as it can. For someone who types 120 wpm, reading or typing a TTY conversation is painfully slow.  By comparison, excluding compression, at the end of the dial up internet era most modems could do 56k, or 56000 baud.  On the other hand, the phone lines don’t need to be very clean or clear to keep up with Baudot.  Also, the conversation was simplex, meaning only one party could communicate at a time. TTY didn’t have any advanced algorithms to enforce this, so it was up to the users to clearly delineate when they were done typing by using the phrase SK (stop keying).  This Wikipedia article (use with caution) has 3 fairly believable sample conversations.

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Telephony 101: Teletypewriter/TTY/TDD

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A teletypewriter is a special device that was typically known as the Telecommunications Device for the Deaf or TDD. These devices act as typewriters that can carry special signals to provide text based communications over voice telephone lines. This was the beginning of using data over the telephone lines.

This technology was invented in the 1960s, nearly a century after Alexander Graham Bell attempted to invent the telephone for this audience, which obviously went for the masses who could speak or hear. The Teletypewriter (known as TTY) was initially referred to leased line that provided automatic printing such as news wire services or even for a console access to mainframes. (In fact, if a customer was very frugal dumb terminals for some were too expensive so computing would result in the typewriter that would automatically “printout” what was coming off the “screen”. A user would respond to commands by typing it into the typewriter which then would relay it to the computer.)

TDD/TTY uses a standardized protocol that basically sends various tones through the telephone lines so the other end would receive the message. According to Wikipedia (use with caution) the change to IP in the traditional phone cloud, would make these devices unusable (including the 500 Rotary telephones) because the complexity of converting landline networks to work in “native” cyber (or packet) worlds. While VOIP enables some analog communications, the move to IP would be easier to service providers to tell users to just send iMessages, SMS, Tweet, IM or other text based technologies instead.

According to various sources, TDD is separate from TTY in the technological sense, and speech impaired users that may have acquired brain disorders; a non verbal, but high functioning form of the autism spectrum disorder; cerebral palsy or other types of speech disorders) are basically non existent users. Or so you think. It’s not to say that people who aren’t deaf can’t use this technology and people with speech impairments have ether used TTY or all the other IP based communications like IM, Web, social media and text messaging.

Because of the similarities of the two platforms, here at The Museum, I believe the term should be referred as TTY as non verbal people are actually disabled users to any telephony technologies as well. Using “TTY” in the generic sense would enable inclusion to all disabled users of this technology.