Payphones have a line reversal to instruct it to commence metering and 3
seconds after this it will be expecting a metering pulse.  (Here a metering
pulse can be a 50hz burst, or a 12khz burst depending on how the payphone
gets back to the exchange.)

I also think that one of the products offered by our carrier is and here is
the spiel
"Customer Loop Metering - keeping track of call costs

Customer Loop Metering (CLM) allows customers to determine the cost of a
call, so that they can charge users of their phones for any calls made. It's
useful for hotels and motels, PayPhones, shared households and the
professional services sector." Telstra

Justin
-----Original Message-----
From: Dipperstein, Michael [mailto:mdippers@HARRIS.COM]
Sent: Friday, 14 December 2001 07:48
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC] Telephone charge system


> 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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