[Asterisk-Users] RFC 2833 and SIP? DTMF? What am I not getting?

[Martin Joseph]

On Mar 16, 2006, at 12:36 PM, Martin Joseph wrote:

So, I am answering my own post (bad form I know)...
>
> I am trying to get my DTMF to use RFC 2833 rather then inband, so that 
> I can utilize lower bandwidth codecs through my FXO.
Ok,  I have given up on this.  There seems to be some kind of deal 
breaker issue with the RFC 2833 support either on the wellgate 3701A or 
somewhere between it and asterisk.

I also figured out that I don't need the gateway to use RFC2833 for me 
to achieve my goals.
>
> After much tinkering I was able to get my gateway (wellgate 3701A) 
> configured to a point where I have some success,  but no real joy.
>
> I have configured the RTP Payload type (or RFC2833 Payload type) to 
> 101.  I don't have a clue what this means,  but I took the 101 from my 
> AG168V ATA's configuration screen, as I know that device seemed to 
> work fine through the old HT-488 fxo(via rfc2833).
>
> I then changed my asterisk extensions for both the FXS and FXO on the 
> wellgate to include dtmfmode=rfc2833.
I now have changed the dtmfmode= in both the wellgate FXS and FXO SIP 
extensions to be "inband".

This seems to work fine.
>
> This has brought me to a point where both my hardphones (ATA's) and my 
> softphones (IAXcomm, or JackenIAX) work perfectly with comedian mail.
Now I realize that Asterisk can handle my off site hardphones via RFC 
2833 and my softphones via IAX2 just fine, and when the tones come from 
those sources(via RFC 2833) asterisk handles the conversion to inband 
and that works ok too.
>
> To me this means that asterisk is properly getting the RFC2833 events 
> from the user agents.
>
> BUT, if I try to dial out the FXO, none of my phones (hard or soft) 
> produce working touchtones for a PSTN based voicemail system.
>
> Even stranger to me, is the fact that from the phone connected to the 
> FXS on the wellgate I can hear tones(listening on a called line), but 
> they sound kind "rough" at the edges.  From the AG168V  I hear no 
> tones,  but what seems to be "blown out" tones (ie overdriven volume). 
>  From the IAX softphones I hear no tones at all just clicks!
>
> Now I would have guessed that the FXO would be doing the conversion of 
> the RFC2833 to inband (for PSTN), so that I thought all the tones 
> should sound the same from any phone?  Apparently this isn't the case 
> at all.
>
> Thanks to all of you for any help understanding and or debugging this 
> mess.
>
I would still love to hear an explanation for the variety of results I 
saw above?  Even a broken wellgate RFC 2833 implementation doesn't seem 
to adequately explain it.  I am sure it's my problem understanding how 
this works?

Thanks,
Marty