From: azur@netcom.com (Steve Schear)
Date: Tue, 14 Jan 1997 22:53:24 -0800 (PST)
To: Eric Murray <ericm@lne.com>
Subject: Re: Newt's phone calls
Message-ID: <v02140b01af020537992b@[10.0.2.15]>
MIME-Version: 1.0
Content-Type: text/plain


>If the person with the cell phone doesn't move, then they don't
>get handed off to a different cell.  That means that they
>stay on the same frquency.  No need to scan channels if they don't switch.

Wrong Eric, cells are constantly expanding and contracting as subscribers
in motion are transferred in and out.  Thus you can be stationary, holding
a conversation, and assigned to cell A when all of a sudden subscribers
enter from adjacent cells B and C threatening to fill cell A beyond
capacity.  To keep from dropping calls in cell A the MTS will determine
which calls can safely, due to signal strength and adjacent cell capacity,
be transferred to another cell.  If your conversation is selected then off
you go to another, geographically overlapping, cell.  The MTS can't be sure
which subscribers are stationary and which are in motion (it really doesn't
care).

We saw this unexpected phenomenon frequently during development of Cylink's
SecureCell and finally had to recommend our users be stationary during use,
because our modems did not tolerate handoffs well without retraining, in
order to offer the best chance of uninterupted communication.

>
>What Bill's saying is that it is difficult to tap the cell phone of
>a _particular_ person with just a scanner.  However the people
>who taped Newt were just scanning for whatever they could get.  That's easy.

Yes, you need a device which can simultaneously listen to the
paging/controll channels and determine, when a handoff to a monitored
conversation occurs,to  which new channel pair they have been assigned.  I
seem to recall such a device was for sale a few years back using a ISA/EISA
card and some DOS compatible software.  It connected to the ubiquitous and
well characterized Oki 900 cell phone.

>--
>Eric Murray  ericm@lne.com  ericm@motorcycle.com  http://www.lne.com/ericm
>PGP keyid:E03F65E5 fingerprint:50 B0 A2 4C 7D 86 FC 03  92 E8 AC E6 7E 27 29 AF