47 C.F.R. § 67.1 : Telecommunication — FEDERAL COMMUNICATIONS COMMISSION — COMMON CARRIER SERVICES — REAL-TIME TEXT — Definitions

(a) Authorized end user device means a handset or other end user device that is authorized by the provider of a covered service for use with that service and is able to send, receive, and display text.
(b) CMRS provider means a CMRS provider as defined in §20.18(c) of this chapter.
(c) Covered service means a service that meets accessibility requirements by supporting RTT pursuant to part 6, 7, 14, 20, or 64 of this chapter.
(d) RFC 4103 means IETF's Request for Comments (RFC) 4103 (incorporated by reference, see §67.3 of this part).
(e) RFC 4103-conforming service or user device means a covered service or authorized end user device that enables initiation, sending, transmission, reception, and display of RTT communications in conformity with RFC 4103.
(f) RFC 4103-TTY gateway means a gateway that is able to reliably and accurately transcode communications between (1) RFC 4103-conforming services and devices and (2) circuit-switched networks that support communications between TTYs.
(g) Real-time text (RTT) or RTT communications means text communications that are transmitted over Internet Protocol (IP) networks immediately as they are created, e.g., on a character-by-character basis.
(h) Support RTT or support RTT communications means to enable users to initiate, send, transmit, receive, and display RTT communications in accordance with the applicable provisions of this part.

47 C.F.R. § 67.1

82 FR 7707, 1/23/2017