[asterisk-users] Using voice modem as poor man's FXO in Asterisk 1.8

[Steve Underwood]

On 02/28/2011 10:12 AM, Stuart Longland wrote:
> Hi all,
>
> I've tried researching this, and so far, have struggled to find any
> contemporary information on the issue, so I do apologise if asking this
> irritates people who have answered this before.
>
> I have managed to set up Asterisk 1.8 on the web server here.  I have
> two softphones (Ekiga) able to communicate with it.  So far so good.
> I'm now curious to see if I can link it with the PSTN phone line here.
>
> The web server in question is an Intel Atom system with a Mini-ITX
> motherboard.  Its one and only PCI slot is occupied by a PCI ethernet
> card.  So FXO card is not an option even if it were within budget.
>
> My options therefore look to be an external FXO device of some
> description (Ethernet or USB), or to use a voice modem.  I fear external
> FXOs are going to be even more expensive than internal FXO cards.
>
> Now, I have here an old Maestro JetStream 56k modem here that does
> amongst other things, voice comms, and I have used it in the past as a
> telephone by plugging a headset into the front of it (and it was full
> duplex too if I recall correctly).  I have also used it as an answering
> machine, with the audio being transmitted digitally over the RS232
> link.  So that to me suggests it is possible to get audio in to and out
> of the modem, either via a sound card or using the serial port.  The web
> server has a sound card too (hard not to buy a motherboard with one
> these days).
>
> Apart from the lack of any hardware signal processing, it seems all the
> components are there.  The server isn't particularly heavily loaded, and
> thus I see no reason why the machine wouldn't theoretically be able to
> handle the DSP in software … I've seen lesser hardware do quite
> sophisticated DSP in real-time.
>
> Now, I've hunted high and low for where this is configured.  Some
> mailing list threads point me to the nonexistant
> /etc/asterisk/modems.conf.  One points me to /etc/asterisk/phone.conf,
> but nothing there jumps out at me as being an obvious means for
> configuring a modem — nor can I find where it's documented on the
> Asterisk wiki.
>
> Where abouts should I look for documentation on configuring these modules?
>
> Regards,
There is no requirement for DSP. There is a requirement for getting 
duplex audio in and out of the PC. *Very* few full blown external modems 
will do that. The very simple USB winmodems will, but nobody has 
produced drivers to make it work for any of the common chips used in 
those devices. Its not hard to do, though. Source code exists which is 
not a million miles from that required to hook a USB winmodem into DAHDI.

Steve