Covers requirements for modems and associated call setup equipment for connection at an NTTP or through an NTTP port to the British Telecommunications public switched telephone network (PSTN). Applies to self contained modems and to modems incorporated within terminal equipment (integral modems) to provide intercommunication facilities over the PSTN. Does not apply to apparatus approved under Section 16(2) of the British Telecommunications Act (1981) before this standard comes into effect, nor to apparatus connected with the consent of British Telecommunications to any British Telecommunications network for development purposes or when under test.