From: tmkk@uiuc.edu (Khan)
Subject: Re: The Zen of CID
Organization: University of Illinois at Urbana
Date: Thu, 15 Oct 1992 14:05:42 GMT


In article <1bi7fsINN8eh@iskut.ucs.ubc.ca> pdivine@unixg.ubc.ca (Patrick Devine) writes:
>
>CID is conceptualy very easy.  Party 1 picks up his or her phone and
>decides to make a phone call to Party 2.  After the phone has been dialed,
>it connects to the main office (or switching network, or whatever).  The
>main office computer has a list of all of its subscribers/whatever.  The
>computer database figures out Party 1's phone number, and then patches the
>call through to Party 2, and places the data packet with the CID
>information on the end of the ring.  Party 2's CID machine interprets the
>information sent and can figure out who is calling beforehand.

OK so far.

>>Is it possible to make a little "black box" that will allow you to 
>>put any CID on your outgoing call and noone will ever discover it?
>
>masking you phone number is very plausible, and I'm sure there are box
>schematics out there to do it.  I'm sure you could even mask your phone
>number well enough that your phone company does not even know who is
>placing the call.  (free long distance calls?)

Please explain how this is possible.

You've already stated that the CNID data orignates at the CO switch, NOT
from your phone at home. How can you prevent the switch from "knowing"
which pair of wires your call is coming in on (and therefore knowing
what CNID info to put into the data packet)?

Analogy time:
Your phone is connected to the CO by a pair of wires called the local
loop. These wires are like a water pipe; whatever you put into the pipe
at your end comes out the pipe at the other end. No matter what your
"black box" does to the signal coming through the pipe, that signal
still comes out of the other end of the same pipe, and the CO end of the pipe
has your number on it.

You can dye your water green, you can make it into Jell-O, you can mix
it with mud, you can do whatever you want to the stuff before you send
it down the pipe, but whatever it is it still comes out of the pipe with
your phone number printed on it. I suppose you *could* mix the water with
quick-hardening concrete; that would certainly block the pipe, but that
might defeat the whole purpose of the exercise. ;-)

The point is, in order to "mask" your number, you would somehow have to
make your water go into your end of the pipe and magically teleport into
a different pipe so that it would enter the CO through a pipe with a
different number printed on it. Please tell me the secret of your
teleportation magic; I'd love to know about it.

Currently, the only way to "mask" CNID information (on systems which
don't allow blocking) is to call a service like 1-900-STOPPER. This
service has nothing to do with the phone company; it's a privately run
service which charges a certain amount per minute. You dial that number,
and their machine answers. Your CNID is delivered to the machine, which
promptly discards the information. You then enter the number you wish to
call. The machine dials that number on a separate line, and when the
connection is made, the machine bridges the two lines together. The
called party still receives CNID, but it's the ID of the STOPPER phone
machine, not *your* number.

This is the best you can do with the current telephone technology. You
still claim it's "plausible"? OK, prove it. Show me some plans for a
black box that will mask my number from the phone company CO on my local
loop.

For more information on how CNID really works and why you can't block it
with some "black box," check out comp.dcom.telecom.