asterisk users - Jan 2010 - DTMF detection on dahdi with b4xxp (again, some more details)

Hi,

I tried again getting DTMF detection on my ISDN devices with dahdi going 
again. I used the channel debug to see whether asterisk sees the frames 
and detects them as DTMF.

Interestingly here's what works:

1. GSM phone -> chan_dahdi g1 -> asterisk -> can_sip -> SIP phone

Both the GSM phone and the SIP phone can issue DTMF that will be 
detected as features (transfer)

2. GSM phone -> chan_dahdi g1 -> asterisk -> chan_dahdi g4 -> ISDN
phone

The GSM phone can issue DTMF that will be detected. The ISDN phone 
won't. (That's my issue.) I don't see any messages of asterisk 
recognizing the DTMF frames when pressing the keys. I do hear the DMTF 
sound on both phones.

3. ISDN phone -> chan_dahdi g4 -> asterisk -> chan_dahdi g1 -> GSM
phone

The ISDN phone can issue DTMF that will be recognized and so does the 
GSM phone.

So. When the ISDN phone is receiving a call on g4 its DTMF sounds won't 
be recognized. OTOH when the GSM phone on g1 is being called it's sounds 
are recognized.

Sounds like a configuration issue to me. Does anybody have an idea what 
to look out for?

Thanks in advance,
Christian

-- 
Christian Theune ? ct at gocept.com
gocept gmbh & co. kg ? forsterstra?e 29 ? 06112 halle (saale) ? germany
http://gocept.com ? tel +49 345 1229889 0 ? fax +49 345 1229889 1
Zope and Plone consulting and development

Hi,

Am Dienstag, den 05.01.2010, 15:38 +0100 schrieb Christian
Theune:
> Hi,
> 
> I tried again getting DTMF detection on my ISDN devices with dahdi going 
> again. I used the channel debug to see whether asterisk sees the frames 
> and detects them as DTMF.
> 
> Interestingly here's what works:
> 
> 1. GSM phone -> chan_dahdi g1 -> asterisk -> can_sip -> SIP
phone
> 
> Both the GSM phone and the SIP phone can issue DTMF that will be 
> detected as features (transfer)
> 
> 2. GSM phone -> chan_dahdi g1 -> asterisk -> chan_dahdi g4 ->
ISDN phone
> 
> The GSM phone can issue DTMF that will be detected. The ISDN phone 
> won't. (That's my issue.) I don't see any messages of asterisk 
> recognizing the DTMF frames when pressing the keys. I do hear the DMTF 
> sound on both phones.
> 
> 3. ISDN phone -> chan_dahdi g4 -> asterisk -> chan_dahdi g1 ->
GSM phone
> 
> The ISDN phone can issue DTMF that will be recognized and so does the 
> GSM phone.
> 
> So. When the ISDN phone is receiving a call on g4 its DTMF sounds won't
> be recognized. OTOH when the GSM phone on g1 is being called it's
sounds
> are recognized.
I *think* there are two possibilities to transfer DTMF on ISDN:
- as audio on B-Channel
- as Key-Press events (Info-Elements) on D-Channel

DTMF on GSM can not be signalled as audio (because of codec with high
compression). I guess in case GSM => asterisk via "chan_dahdi g1"
in
Your example, the DTMF is signalled as Info-Elements on D-Channel.

I guess in the cases where Your DTMF is not working, audio path is used.
In this case DTMF detection is done by DSP-Software. Look for the
relaxdtmf statement (in case of zaptel this worked for me in a simmilar
scenario).

HTH,

Karsten