[asterisk-users] Double DTMF digits

[Remi Quezada]

I wonder if the your hardware is doing the actual DTMF detecting.   What 
hardware are you using?  I'm using the  TE205P and I believe that the 
DTMF detection is being done in the software. 

Remi

Steve Davies wrote:
> On 5/3/07, Ken Leland III <k3leland at monmouth.com> wrote:
>> When dtmfmode is set to inband for SIP, and i originate a call from sip
>> out to the PSTN, I can hear the DTMF digit twice in the audio stream.
>> Once very briefly and once for normal duration.
>>
>> Our Theory: While Asterisk is parsing the DTMF, for a fraction of a
>> second, while the end user generated DTMF is being detected, the DTMF is
>> passed inband. Once the DTMF is detected Asterisk silences it and
>> regenerates it. Sensitive machines like auto attendants pick up both the
>> brief end user generated tone as well as the full length asterisk
>> generated tone and ultimately perceive each digit twice.
>>
>> Is anyone else experiencing this?
>>
>> I have reproduced this in an environment
>>     * with one asterisk server that is both the feature server and the
>> media gateway, and is timing off of network T1s
>>     * with two servers, one feature server (timing off of ztdummy) and
>> one media gateway (timing off of network T1s) using IAX as the inter
>> asterisk protocol
>>
>> It is pretty easy to reproduce:
>> -Dial a PSTN number(like your cell) from a sip phone using inband DTMF,
>> and configured in asterisk sip.conf with dtmfmode=inband.
>> -Answer the PSTN end.
>> -Press and hold a digit on the sip phone. On the PSTN phone you will
>> hear a very brief, end user generated, tone.
>> -Let go of the digit on the sip phone. On the PSTN phone you will hear
>> the asterisk generated tone.
>>
>> Can anyone else hear the brief initial tone?  Any help is greatly
>> appreciated!
>
> Yes, we have a similar issue, but do not normally use inband DTMF
> because SIP phones very  cleanly generate rfc2833 RTP packets directly
> and remove this issue.
>
> On the other hand, asterisk is not alone dealing with this issue in
> SIP. The Linksys ATAs have exactly the same issue.
>
> Strangely, I do not have a problem receiving inband DTMF through
> Zaptel, which I believe uses the same DSP code for DTMF detection...
> Or does it?
>
> Steve
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