International call progress tones for IP-PBX and VoIP telephony

Telephone Line Signalling

Tone dialing

  • Tone dialing uses DTMF tones. The acronym DTMF stands for dual-tone multi-frequency.
  • Duration is typically 100 ms with an interruption of 100 ms.
  • DTMF signals consists of a pair of tones, one from the low group (697,770,852,941), and one from the high group (1209,1336,1477,1633), yielding 16 combinations.
  • Nominal levels are -9 dBm for the higher frequency tone and -11 dBm for the lower frequency tone. The difference in level is known as 'twist'.

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Related product: CPT-Master tone generator app