[Asterisk-Users] dtmfmode=inband but SDP also indicates rfc2833

[Stagg Shelton]

I answered my own question.  My objective was reached with a simple 
return statement on line 4384 of chan_sip.c in asterisk 1.2.9.1 ftp 
download.  The effect that this has is that asterisk will return a 200 
OK that indicates in the SDP that only inband DTMF is supported.  My 
carrier detects this and their NexTone Session Switch sends out dtmf  
inband.

It sucks having to force asterisk to operate in this manner, but 
hopefully asterisk implementation of rfc2833 will get the bugs worked 
out, if they are in fact bugs, and not design desicions.

Stagg Shelton wrote:

> I'm trying to figure out a way around a problem that I'm having.  My 
> carrier sends me a SIP INVITE that indicates that the dtmf modes 
> available are inband (0), and rfc2833 (101).  My asterisk server 
> (1.2.9.1) sends back a 200 OK message and shows in its SDP Media 
> Description that we accept inband (0) and rfc2833 (101).  My carrier 
> therefore sends all DTMF via rfc2833 which obviously causes problems 
> since asterisk is configured for inband.
>
> I've tried going pure rfc2833 with the carrier, and am having DTMF 
> related problems.  From the research that I have done with my issue it 
> seems to be a problem with the way asterisk sends the rfc2833 packets 
> out at nearly the same time.  Altering the timing that asterisk uses 
> to send the rfc2833 packets seems too deeply seated in asterisk.  I 
> therefore have settled on the idea on using inband for dtmf.  My 
> termination tests using inband have been successful.
>
> So here is what i think will solve my particular problem.  I just want 
> to respond with a 200 OK that does not contain anything about rfc2833 
> in the SDP.  Is this fairly doable.  I've been diging through 
> chan_sip.c and think I could just make a couple of modifications to 
> make asterisk do what I need it to.  I'm hoping to have someone who is 
> familiar with chan_sip.c enlighten me as to whether or not this can be 
> done, and what functions I would need to modify in order to make it 
> happen.
>
> Thank You
> Stagg Shelton
> www.oneringnetworks.com
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