[asterisk-users] Handling DTMF for number 4

[Gareth Blades]

Alejandro Cabrera Obed wrote:
> Dear all, I have Asterisk 1.4.23 implemented with an IVR wainting for
> mobile phone calls coming from a GSM Gateway.
> 
> All the components are set up in DTMFMODE = RFC2238, and so when the
> caller from mobile touches the IP phone LAN extension, the call is
> succesfully established. Everything is OK except for the DTMF for
> number 4, because if the caller from mobile dial 1004 or 1014
> extensions -which have the number 4- the calls are errouneosly
> established with extension 1000.
> 
> I live in Argentina, but I don't know if the DTMF frequencies are the
> same than other countries or I have to make a change in somewhere.
> 
> Can be a problem with the detection of DTMF for number 4 in Asterisk ???
> 
> Thanks a lot
> 
> Alejandro
> 

The gsm gateway would be performing the DTMF detection and just sending 
on what it detected as you have the DTMFCODE set as RFC. Maybe if you 
set the DTMF mode to INBAND it may pass the audio straight through and 
allow asterisk to detect it.
The problem is that mobile calls are heavily compressed so any entered 
digits are converted to tones once the information reaches the network 
operator. As the call is gong back over a mobile connection the DTMF is 
compressed which results in unreliable detection.