[VoIP] Questions about payphones (was Re: CAMA and UK billing)

[Mark Rudholm]

Jayson Smith wrote:

>      So what you're saying is, a standard four-wire phone cord would do the
> trick as far as all phone service and coin relay control is concerned? So
> could I have him just run a four-wire modular jack or plug, connecting all
> relevant wires, and have all my bases covered?

Yes.  When in real service, these phones are connected to Tip and
Ring from the CO, and a local earth ground.  This way, they are able
to operate on a single wire pair, just like any other phone.

They're quite easy to wire up yourself.  Just buy a modular cord
that has spade lug terminals on one end.  The terminals are clearly
marked "T", "R", and "G", which correspond to Green, Red, and
Yellow, respectively.  But I suppose Phil can do that for you if
you're buying a phone from him.

>      That's what I thought about initial deposit. So, have him set that to
> five cents, so it never becomes an issue.

Yep.  Again, this isn't hard to do yourself.

>      How are you thinking of pulling this off in software? Will there be a
> configuration file with rates and time limits specified? Or will an
> extension need to call an application and specify what rate to charge for
> how long, and if no application call is ever made, the call is free?

I don't intend for this to be a commercially useful project.  To
be commercially useful, you'd want to take an entirely different
approach --like out-of-band coin deposit and control signaling
within the IAX2 or SIP protocol itself, not in-band tones.  One
wouldn't want to repeat the mistakes of Ma Bell :)

I haven't addressed the software configuration issue yet.  DTMF
and MF decoding is done in dsp.c via some simple goertzel analyses.
What I had in mind was to add a fifth row and column to the DTMF
tone set for 1700 and 2200Hz.  This would basically give me another
"digit" to use in the dialplan.  Coin return/collect would be
handled with a shell or PERL script called via AGI.  I was planning
on relying on the functions of features.conf to give me the
ability to detect "buttons" in-call ("buttons" in this case
would be the 1700+2200Hz coin tones).  Beyond that, I haven't
solved it...

Ultimately, I would be able to publish a schematic, some assembly
instructions, a patch set for Asterisk, as well as some
instructions and examples of how to write the conf files.