[MLB-WIRELESS] Free P2P phones will pressure telcos
tlangdon at atctraining.com.au
Wed Nov 12 16:06:02 EST 2003
> Well, it would partly work, but you wouldn't be able to dial
> (afaik) as the
> soundcard input doesn't detect DTMF (afaik). You'd still need
> to dial via
> the software phone.
Hmm, perhaps the IRLP style approach (but with phone handsets and hardware
based line simulators, instead of radios) is the way to setup a VoIP IP
ohone network. The idea is actually quite simple in concept.
1. Define a numbering scheme. This can be a simple "flat" scheme like ICQ
(basically the ham VoIP apps work this way), or something more complex using
international prefixes and the like. I prefer KISS, we're not billing here.
2. Setup some form of address resolution. This could use DNS
(12345.freeipphone.org, etc), or some specialised server based scheme (the
ham systems have their own schemes for address resolution).
3. Define some sort of hardware interface to connect the phone to the PC.
The interface would need to generate ring voltage (80V AC - oscillator,
audio power amp and a transformer should do), and all the necessary voltages
and signalling to make an ordinary POTS handset work. The interface could
also include a DTMF decoder chip so it can perform this function as well.
Alternatively, you could write this function into the software (I have seen
both approaches used, but the hardware one works best). Hardware decoding
also makes it easy to script in special functionity that can be accessed
whenever the phone is off hook, regardless of whether it's on a call or not
(a la IRLP).
3. Start with some existing piece of open source software. Hack it to work
with the above interface for call establishment and termination, so all the
user has to do is treat it like a normal phone - just pick it up and dial
(or answer). For our application, probably one of the SIP based VoIP
packages would be most appropriate.
4. Build on extra functionality outside the package. Shell scripting can
work well here, and make the package very "hackable". That's one of the
strengths of IRLP in the radio world. If the functionality is not there,
chances are you can add it in. :)
Of course, the hardest part will be getting the hardware out there. Now, if
any of us is involved in electronic manufacturing, that would help. Good
thing is it won't need Austel/ACA approval, as it's not interfacing to the
phone line, just your PC. :-)
Might also be a good project for mags like Silicon Chip. :)
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