Re: DTMF info required
DTMF Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the voice-frequency band to the call switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone, and is standardised by ITU-T Recommendation Q.23. A different version is used for signaling internal to the telephone network.
DTMF is an example of a multifrequency shift keying (MFSK) system. Today DTMF is used for most call setup to the telephone exchange, at least in developed regions of the world, and trunk signalling is now done out of band using the SS7 signaling system. The in band trunk signalling tones were different from the DTMF tones known as Touch-Tone, with a two out of six code being used rather than a square matrix.