Voice support methods in contemporary modems

[Marcin Szewczyk]

Hi,

sorry for writing on a devel group but I really did not find any better
place to ask. I am working on a phone-like device that could make a
voice call and sometimes send some data over the internet. I am
confused, probably because most of documentation on voice modems is from
another century.

At first I thought that modems can use the serial interface to send
audio data the same way they do with internet data (TCP/IP). Was it ever
true?  Internet remembers things like FCLASS=8, AT+VTX, AT+VRX and
switching between modes with pause, +++, pause.

I thought that maybe mPCIe modem could do things like that using ttyUSB.

Then I found a thread on the Tizen bugtracker and some documentation on
Sierra and Telit modems. They seem to have an I2S interface on reserved
mPCIe pins.  Is it correct to assume that there is no other way but to
have a motherboard with I2S hardware support or an external ADC/DAC? Can
a regular Atom motherboard do things like that? Is there a de-facto
standard on using some specific pins for I2S on mPCIe and some
motherboards support that by forwarding sound to their Intel HDA for
example?

Then I have also read about QMI and MBIM protocols. Some of articles
mention voice in that context. Are there any devices supporting audio
transfer using just software without any soldering of I2S pins?

Are there any modems that emulate an ALSA sound card?

What are the options with voice support as far as contemporary (mainly
mPCIe) modems are concerned? I know that is a lot of questions but maybe
there is a good read you could provide me with?

Regards,

-- 
Marcin Szewczyk
http://wodny.org