ITU-T Recommendations

Telecommunications relay services enable persons who have hearing or speech disabilities, and who otherwise would be unable to engage in voice telecommunications, to make voice telephone calls to other people. In all forms of relay services, persons with disabilities connect to a communication assistant via a communications medium that is accessible to them. The communication assistant acts as an intermediary in the telephone call and converts between the accessible communication medium and voice, which is relayed from and to the person on the other end of the call.

This Recommendation provides a functional description of four common types of relay services in use today: text relay, video relay, captioned telephone service relay and speech-to-speech relay. Additionally, it lays out specific functional requirements of relay services pertaining to equipment, call setup, call experience, emergency communications, and message retrieval.