OJ`S CELL PHONE

[Phil Karn]

>Technicians in the tracking station can, if necessary, track a
>particular call back to the cell site from which it originates.  But the
>monitoring can not be done unless the phone is in use. [ Is that true? ]

There is an optional mechanism called "registration" by which the
system can keep track of your approximate location even though you're
not actually making calls. The intent is not really to track your
location, although it could certainly be used for that purpose. It's
intended to minimize the amount of "flood paging" that goes on.

When somebody calls you on a cell phone and the system doesn't know
where you are, it has to broadcast the page (the message announcing
the call) on every cell in the system. In large busy systems, this can
cause quite a bit of congestion on the paging channels. So the system
has the option of asking the users to transmit occasionally so the
system can keep track of their location and direct incoming pages to
the last known cell, at least as a first try.

Think of the system as a large bridged Ethernet and you won't be far
off, at least on the concept. On the other hand, the fact that most
cell phones see very little use, and the use that they do see is
predominantly mobile originated, means that registration actually
doesn't buy that much in practice. It can even be counterproductive
because of all that non-revenue generating registration traffic that
takes up capacity on the access and paging channels. This probably
explains why registration isn't often used in practice, as far as I
know.

The best way to make sure it isn't occurring, of course, is to turn
off your phone.

Phil