Are there any 'pay phones' that use ISDN loops
to signal the local serving 'switch' - and also
receive signalling from the local switch indicating
'call state' and 'call progression'?

By using ISDN - you would receive notfication and send
control in digital to/from the local 'switch' which is
your interafce into the telco network. The ISDN I/F
would notify you (as it does for all phases of a call)
if the far end picked up on the call, as the call's
*voice circuit* is not cut through (this saves the LD
network provider money) until a call is actually picked
up on the far end ... unless the far-end 'terminating'
switch is something old that doesn't speak SS7 back
into the network ...

Jim


----- Original Message -----
From: "Larry Williams" <wizzzard@BELLSOUTH.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, December 13, 2001 11:18 PM
Subject: Re: [PIC] Telephone charge system


> Assuming you are making product for the US, having worked in the
> payphone manufacturing and design, I can say that it is simple, yet can
> be frustrating. To detect an answer, a teltone M980 can detect the click
> when the called party answers. However, the M982 and M984 are used for
> precise ring, busy, and intercept tone detection.  Current day phone
> switches will give the caller the "This number is busy" message which is
> impossible to detect from a true answer.  You could spend a lot of time
> just revising the software for the different rings you will encounter.
> Some switches give a battery reversal on answer and hangup.  There are
> so many oddball rings and busy signals from small independent phone
> companies that you will never be able to get 100% accuracy in
> detection.  You can get operator screening on the line to prevent
> collect and third party billing to you number.  Hook flash for call
> waiting and three way calls CAN be detected.  We did it for prison
> phones.  For that, we used a dial click detector, the same one used to
> read a rotary dialed number from the far end for collect calls.  On
> answer detect, simply put, look for a ring, then after one ring, start
> looking for a pop, when the circuit connects through, then for voice,
> using the M980. If no pop or noise, don't forget to look for second or
> subsequent ring after the apparent answer. Timing of rings, normally
> 2sec on 4 sec off, BUT, non standard rings CAN, and sometimes ARE, a
> little off on timing.
> A truly accurate answer detect circuit would be worth a fortune to the
> developer. Even the ultra modern cellular companies use call duration to
> start the call billing.  Some long distance companies do the same
> because answer detect for the destination phone company may not be
> transferred to the company where the call originated.
> GOOD LUCK!
> Dipperstein, Michael wrote:
> >
> > > From: XARA Telecomunicaciones [mailto:xara@velocom.com.ar]
> > >
> > > Hi,
> > > I'm developing a PIC based telephony rate system
> > > I need to identify when the called party pickup the phone
> > > any Ideas?
> >
> > I think you might have a little trouble here.  Generally, there is no
signaling
> > to the calling party that the called party has answered the phone
(unless you
> > count "hello").
> >
> > There are all kinds of call progress signals that indicate that the
called party
> > has not answered the call, and maybe you can use their absence as an
indication
> > of an answer.  Unfortunately, most of those signals are in the audio
band, and
> > probably need to be analyzed in the frequency domain (maybe with a
dsPIC).
> >
> > Just off the top of my head, the following signals mean that the call
was not
> > answered:
> > - Calling party hangs up
> > - Ringback (ringing caller hears)
> > - Busy
> > - Fast busy
> > - Intercept (tones followed by message)
> >
> > There are also some nasty scenarios that you need to be able to handle
to get a
> > good count:
> >
> > 1. Conference calling (three-way calling).  Here someone can call you,
and you
> > can call someone else without ever hanging up.  You will be billed for
the
> > outgoing call.
> >
> > 2. Call someone, then receive a call on call waiting.  Switch to the
other call,
> > and some time later the person on the first call hangs up.  You will
only be
> > billed for the time the first person stayed on the line.
> >
> > 3. Receive a call with reversed charges.  You will be billed, but didn't
make a
> > call.
> >
> > 4. Receive an automatic call back when a busy number that you were
trying to
> > reach became unbusy.  I think you get charged for the call back.
> >
> > I'm sure that I left several conditions out.  I know that in the good
old days
> > people made equipment that did what you're trying to do, but I don't
know if I'm
> > over looking something, or the network has become more complicated since
those
> > days.
> >
> > -Mike
> >
> > --

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