A question for the techies:

When you press the DTMF keys during a call on a GSM mobile, do the
tones get sent in-band in the audio stream (not very reliable with
compressed codecs), or are they sent as event packets in a simlar
way to RFC2833 and SIP INFO on VoIP?

The reason I'm asking is that I have an Asterisk box taking SIP calls
from a PSTN->VoIP gateway run by a telco in Singapore. If I call the
Singapore access number from a UK landline, DTMF is correctly detected
and passed over SIP and/or RTP to Asterisk. If I call instead from my
Orange mobile (Nokia 6310i), the DTMF seems to get lost and never
reaches Asterisk.

I was wondering whether it is trying to travel in-band all the way to
Singapore, or being converted to out-of-band somewhere.

Cheers
Tony
--
Tony Mountifield
Work: [email protected] - http://www.softins.co.uk
Play: [email protected] - http://tony.mountifield.org


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