Modem taps/Caller ID

The recent discussions of tapping modem transmissions reminds me of
a scrap of data I saw about Caller ID [the service provided by the 
phone company that displays the caller's phone number whenever your
phone rings]. Supposedly, the phone company transmits the caller's 
number as a burst of 1200 or 2400 baud ASCII between the first and
second rings; if your modem is set up 'just right,' you can capture
the number with a PC.

[Sorry there is so little data to go on; this tidbit appeared on a 
PC bulletin board and there was no follow-up discussion.]

Does anyone here know more about this? I would dearly love to set up a
program on the PC in my basement that could capture Caller ID data and
log it in a database. Obnoxious callers (Olan Mills, local telemarketers,
etc.) could be identified easily, and I could program the modem to pick
up / hang up on those calls. Then, I could ignore the phone until the
third ring; my PC would automatically dispose of nuisance callers as soon
as the Caller ID data was processed. Also, I'd build up a database of 
names and phone numbers important to me - maybe I'd spend less time 
scrounging my pile of Post-It notes looking for phone numbers.

........................................................................
Philippe D. Nave, Jr.   | The person who does not use message encryption
pdn@dwroll.dw.att.com   | will soon be at the mercy of those who DO...
Denver, Colorado USA    | PGP public key: by arrangement.

> 
> The recent discussions of tapping modem transmissions reminds me of
> a scrap of data I saw about Caller ID [the service provided by the 
> phone company that displays the caller's phone number whenever your
> phone rings]. Supposedly, the phone company transmits the caller's 
> number as a burst of 1200 or 2400 baud ASCII between the first and
> second rings; if your modem is set up 'just right,' you can capture
> the number with a PC.

The number is transmitted in ascii at 1200 bits per second.  The
standard used to transmit the data is not the "normal" 1200 bps
mode of your modem.  Normally 1200 bps is accomplished by sending
300 symbols per second where each symbol conveys 4 bits of information.
The caller ID info is transmitted at 1200 bps by sending 1200 symbols
per second where one symbol conveys 1 bit of information.  The method
used is FSK,  one frequency is sent for a 1 bit, and another for
a zero bit.  I dont have the frequencies on me, but if you are 
really interested I can get them to you later.

I have no idea how you would get your modem to go into the right
mode (and how it would react to data on the line before it goes
off hook). 

> Philippe D. Nave, Jr.   | The person who does not use message encryption
> pdn@dwroll.dw.att.com   | will soon be at the mercy of those who DO...
> Denver, Colorado USA    | PGP public key: by arrangement.

Philippe Nave" <pdn@dwroll.dw.att.com> asked:

> Does anyone here know more about this? I would dearly love to set up a
> program on the PC in my basement that could capture Caller ID data and
> log it in a database. Obnoxious callers (Olan Mills, local telemarketers,
> etc.) could be identified easily, and I could program the modem to pick
> up / hang up on those calls.

Supra offers CallerID as an option on their high speed modems.