03.143GPPSupport of Dual Tone Multi-Frequency Signalling (DTMF) via the GSM SystemTS
Dual Tone Multi Frequency (DTMF) is an inband one out of four plus one out of four signalling system, primarily used from terminal instruments in telecommunication networks. The international recommendations which apply are CEPT recommendations T/CS 34-08 (sender) and T/CS 46-02 (receiver) as detailed in sections 6.2 and 6.3. For PCS 1900 for North America the Standards which apply are operator specific.
In the GSM system the MSC must support DTMF in the mobile to land direction.
The support of this facility in the land to mobile direction is for further study.
The use of DTMF is only permitted when the speech teleservice is being used or during the speech phase of alternate speech/data and alternate speech/facsimile teleservices. The responsibility for checking this lies in the MS.