From: Bill Stewart <bill.stewart@pobox.com>
Date: Wed, 7 Jan 1998 13:22:52 +0800
To: Alexandre Maret <rp@rpini.com>
Subject: Re: Location Escrow anyone ?
In-Reply-To: <c=AU%a=TELEMEMO_%p=TAFENSW%l=ISF10-980102034537Z-4222@ixf2m1.isd.tafensw.edu.au>
Message-ID: <3.0.5.32.19980106184201.00832180@popd.ix.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain



Tracking your position in real time is one thing - recording the tracks
is quite another.    The system does need to know, in real time,
the cell for each phone that's currently talking,
and needs to know quickly where any phone that's being called is
(could be implemented either by constantly tracking every phone,
or by sending out requests when the call is made,
probably starting with the usual suspect locations and then
branching out farther, or using some kind of roaming notification.)

But does it need to know where you've been?  It wouldn't be surprising
if the telco recorded location (at least cell site) at the beginning
of each call, to resolve billing disputes with customers,
and of course they record minutes of use and roaming information
for users who make calls outside their home territory.
They probably also record calls per cell site and handoff information,
but probably not by user.

For police purposes, if you want to find somebody right now,
and the cellphone system can only give you precise locations right now,
just call them - "Hey, Suspect!  We know where you are,
and it's costing you money for us to call you and tell you!
Have a nice day!" - and the system knows even if they don't answer.

At 02:42 PM 01/03/1998 +0100, Alexandre Maret wrote:
>If they store the location of your phone every 3 secs, for 6 month,
>this means 5'241'600 locations. Printed on 70 lines/page paper,
>this means 74'880 A4 pages. Do you think they'd be happy to print
>and send you 74'880 pages for 300SFrs ?

They could probably deliver it on industry-standard 9-track tape :-)
5 bytes is enough to locate you within 62m anywhere on Earth
- 16 bits gets you 1km of lat or long on a 40000km planet),
though 4 bytes is probably enough to identify a cell plus
some precision bits since the whole planet doesn't have cell sites.
So it's really only 20-25MB of data per user to track that much data,
and it compresses extremely well (e.g. 1 byte/sample is plenty for
phones that are moving, and run-length coding radically reduces the
location of the phones that aren't moving, which probably
covers 23 hours a day for most people.)  Call it 250KB/day, max?
I'd be surprised if they really kept that much, and the economics are bad,
but they could do it, and they'll be much happier to mail you a floppy
of compressed data for your 300 francs, or print it in very tiny print...

				Thanks! 
					Bill
Bill Stewart, bill.stewart@pobox.com
PGP Fingerprint D454 E202 CBC8 40BF  3C85 B884 0ABE 4639