The teletypewriter (TTY) was developed in 1964 by deaf inventors James C. Marsters and Robert Weitbrecht to enable deaf and hard-of-hearing individuals to communicate over standard analog phone lines. Using acoustic couplers attached to regular telephones, TTY devices transmitted text via frequency-shift keying and a 5-bit variant of Baudot code at around 45.5–50 baud. Users developed their own shorthand conventions (GA for 'go ahead', SK for 'stop keying'). Telecommunications relay services, first established in 1974, allowed TTY users to communicate with non-TTY users through human operators. While largely superseded by SMS and internet messaging, TTY remains in limited use and compatibility efforts continue especially for emergency services.
Sort: