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.
—
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.