Dual Tone Multi-Frequency (DTMF)

Dual-tone multifrequency (DTMF), also known as Touch Tone, is used for telephone signalling over the line in the voice frequency band to the local exchange. Prior to DTMF the phone systems had used a system known as pulse dialling to dial numbers, which works by rapidly disconnecting and connecting the calling party's phone line, like turning a light switch on and off.

The multi-part ETSI Standard ES 201 235 specifies how to apply the Dual Tone Multi-Frequency (DTMF) signalling system to transmitters and receivers. It conforms to the International Telecommunication Union (ITU-T) Recommendation Q.23: 'Technical features of push-button telephone sets', and it provides a complete set of requirements for all applications intending to use DTMF signalling.

The level of detail enables manufacturers of telecommunications equipment incorporating DTMF signalling to design the equipment such that it facilitates highly reliable signalling. It applies to DTMF signalling in the local access network, in which the transmission path between transmitter and receiver corresponds to a 2-wire analogue subscriber line, as well as to DTMF signalling over an end to end transmission path in the telecommunication network.

The European Standard EN 300 659 specifying the subscriber line protocol over the local loop for display (and related) services includes an annex which specifies the DTMF based subscriber line protocol for the support of PSTN display services at the Terminal Equipment (TE).

ETSI Standard ES 200 778 specifies the electrical characteristics and the functional characteristics for TE connecting to the Network Termination Points (NTP) of a Public Switched Telephone Network (PSTN) interface and providing the protocols based on EN 300 659 over the local loop for display and related services.

The following is a list of recently published and frequently downloaded standards. Please use the ETSI Work Programme to find further related standards.