36 CFR Part 1194 - Information and Communication Technology (ICT) Final Standards and Guidelines (with amendments issued through Jan. 2018)

TTY.

Equipment that enables interactive text based communications through the transmission of frequency-shift-keying audio tones across the public switched telephone network. TTYs include devices for real-time text communications and voice and text intermixed communications. Examples of intermixed communications are voice carry over and hearing carry over. One example of a TTY is a computer with TTY emulating software and modem.