[Blink] DTMF not supported

Andreas Sikkema ASikkema at office.unet.nl
Thu Jul 22 18:29:05 CEST 2010

> Dtmf is sent as signaling in the rtp stream. It does not have a 
> 'duration' only inband dtmf (you can enable it in blink, it plays a 
> wav file) can have a duration. The equipment you mention must read 
> dtmf from the rtp stream, and it seems it does not do it properly. 

RFC2833, 4.4, payload format:
The payload contains the following fields:
      duration: The duration of the tone, measured in timestamp units.
           The tone begins at the instant identified by the RTP
           timestamp and lasts for the duration value.

It is a little arcane but I have seen it being used (Asterisk 1.0 IIRC) 
and I'm sure the gateways into PSTN will honour the values. Sending 
RFC2833 events can be quite a lot more complicated than just sending a 
single message ;-)

Andreas Sikkema

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