atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telephone Repairs & Equipment Viking AR-1 (autoattendant) incompatibility with cellphone gateway

I did a little sniffing around, and apparently to carry DTMF over digital networks (e.g. cell and VOIP), there's a protocol called RTP (Real Time Protocol, e.g. RFC-4733) that traffics voice data, and within that protocol, there's a special handling for "DTMF events", which to ensure DTMF survives intact over networks where the voice compression might be too high, it is instead *parsed* by the analog-to-digital equipment, converted into a separate digital representation of the DTMF digit, transmitted as a small digital data packet, and the audio frequencies are clipped out of the A-to-D conversion, and are converted back to audio at the D-to-A end of the connection, in this case presumably at the cell phone end of things.

So it seems clear that an analog line's DTMF tones are passed as audio over the analog circuit, but at the telco, when the sounds are converted to digital (for transmission over the cellular/wireless network), the tones are first recognized, converted to a digital representation of the DTMF digit, passed as a special RTP packet representation of that digit, and the tone "sound" is /not/ transmitted as a sound frequencies (i.e. clipped out of the analog conversion).

Then presumably at the other end, when the digital data is converted back to analog so as to be "heard" by the analog equipment (e.g. the speaker in your cell phone), the RTP digital version of the DTMF code is supposed to be "regenerated" and inserted back into the voice circuit, so as to be heard as very clear tones.

So the fact the tones aren't making it through from the remote phone to the cell phone, I'm not sure if the cell phone is simply not regenerating the RTP encoded digital version of the DTMF events, or if the cell service (e.g. AT&T) is simply capturing the DTMF events for itself (such as for remote access voice mail features, or to prevent the remote caller from accidentally accessing DTMF oriented features as a security measure).

Either way, this seems to be eclipsing the DTMF sounds from being "heard" by the Xlink, and Viking AutoAttendant.

So I'm not sure, but this actually sounds like it might be an issue for AT&T to weigh in on, or possibly the cellphone (Apple iphone).

Anyway, "ugh", I guess I should take this question now to a cell phone/VOIP oriented forum or take it to AT&T itself, it's not really a phone equipment problem.