Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: telephone Caller ID
Message-ID: <1991Jan3.163735.23511@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <1991Jan2.183802.13412@amd.com>
Date: Thu, 3 Jan 91 16:37:35 GMT

In article <1991Jan2.183802.13412@amd.com> lpdjb@brahms.amd.com (Jerry Bemis) writes:
>How is the caller ID encoded on the phone lines?

If you subscribe to caller ID, and the caller is ID-able (i.e. not calling
from the other side of an ancient non-computerized exchange), you get a
burst of modem tones between (as I recall) the first and second ring.
It's one of the old 1200-baud modem encodings, I think.  You get it only
once, and there is no parity or other error detection/correction.

Note that you must subscribe to, and pay for, caller ID.  Contrary to some
mistaken rumors, it is not automatically provided on all phones.  On old
exchanges, it is not available at all.

>Is there an answering machine that records it on the market?

I'm not aware of one, but if it doesn't already exist, I'm sure people
are working on it.

>Is there a simple way to display the callers phone number?

Nothing trivial, given that you need half a modem to even decode the tones.
-- 
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu   utzoo!henry