[Asterisk-Users] DTMF Simultaneous Inband and RFC2833 performed by Asterisk => Duplicate tones

[steve at daviesfam.org]

On Wed, 18 Jan 2006, Kevin P. Fleming wrote:

> Max Glucksmann wrote:
> 
> > - RFC2833 standard configured on both end-points.
> 
> If this is the case, but the end sending DTMF _also_ puts it inband, 
> then it is broken. This is an either/or setting; it's either inband or 
> out of band, but not both.
> 
> Asterisk sometimes listens for inband DTMF even when RFC2833 has been 
> specified because the SDP tells us what the peer wants to _RECEIVE_, not 
> necessarily what it will send. There are devices out there that will 
> tell us they want RFC2833 but send only inband... many devices are just 
> broken and/or inconsistent.

Hi Kevin,

I have seen the following effect in Asterisk, though:  where it converts 
an inband DTMF (eg coming off a Zap channel) into an indication, it mutes 
the audio where that tone is.  But sometimes it leaves a teeny bit of the 
tone behind.

If you take such a call over say IAX to somewhere and then back out a Zap 
channel, you end up with the teeny remaining bit of the original tone, 
PLUS the regenerated tone.

If you are very unlucky a remote DTMF receiver can hear two digits.

Steve