[Rack] Modem over VoIP Experimentation

Jonathan Lassoff jof at thejof.com
Sun Nov 28 08:09:50 UTC 2010

On Sat, Nov 27, 2010 at 10:24 PM, Jake <jake at spaz.org> wrote:
> can't you just simulate the modem data in software and pretend to be a
> "modem" with the VoIP client?  Actually that sounds like a bit of work..

That would be way cool and a nifty hack. At lower bauds, I'm sure it's
pretty do-able. There is a similar modem implemented for amateur radio
in Linux called soundmodem that's pretty cool. Since most of the AX.25
stuff is only 300, 1200, or 9600 baud doing the processing on a CPU
capturing digital sound is pretty doable.

>> So far, I'm having trouble getting data to/from dial-up BBSes so far.
>> It'll detect a carrier and connect, but I'm not seeing any prompts.
> maybe it has something to do with the firewall?  I have been unable to get
> any connections through the firewall to the robot even though someone very
> kindly allocated an IP for it...

I think any firewall interference is unlikely. It's all on the local
network and the media stream is getting established, it's something to
do with the actual negotiation between the modem and the coupler.

I opened up the acoustic coupler, and it doesn't seem like there's
much in the way of smarts in there. I suspect it's just a dumb modem
-- in the literal sense of the word. In which case, I think it can
only make calls out and can't answer them. Still pretty useful for my
purposes on the "telecom shelf".


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