Howto:How are DTMF signals treated in the media stream?

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FAQ: How are DTMF signals treated in the media stream?



DTMF tones found in the media stream on an analog or ISDN interface is removed from the media stream and sent separately as H.245 userInput, as defined by the standard. This is also true for the innovaphone IP Phones when DTMF tones are detected in the handset.

Reversely, the DTMF tones are regenerated from the H.245 signalling towards the analog or ISDN network.

We currently do not support DTMF transport though the RTP data stream.

Tools clipart.png FIXME: "this informastion is out-of-date and needs a rewrite"


SIP in-band DTMF and

SIP out-of- band DTMF

according to RFC 2833

Known Problems

Sporadic false DTMF detect

Solution: Option added to configure DTMF detection sensitivy. (available since V7 hf16, ip800, ip1200, ip4001, ip6000 only!)


config change AC-DSP0 /dtmf-threshold <val> 

to change the sensitivity.

  • 0 selects -38dBm ( default),
  • 1 selects -28dBm,
  • 2 selects -33dBm,
  • 3 selects -43dBm,
  • 4 selects -48dBm

Related Articles

Support:DTMF interworking between SIP and H.323 fails