On 4th August 1998 the European Council Decision regarding the CTR 21 has
been published in the Official Journal of the EC. The CTR 21 applies to all non
voice terminal equipment with DTMF-dialling which is intended to be connected
to the analogue PSTN (Public Switched Telephone Network).
CTR 21 (Common Technical Regulation) for the attachment requirements for
connection to the analogue public switched telephone networks of terminal
equipment (excluding terminal equipment supporting the voice telephony
justified case service) in which network addressing, if provided, is by means of
dual tone multi-frequency signalling.