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 multifrequency signalling.