covert@covert.enet.dec.com (John R. Covert 09-Jun-1990 1015) (06/09/90)
>A friend of mine wants to have two cellular telephones in two >different cars with the same telephone number. Of course, he will use >only one at a time. The telco won't set this up for him. This really isn't technically possible. Even if he promises to never turn power on to both of them at the same time, accidents do happen. If power were on to both units at the same time, both units would respond to commands from the cells, and bad things would happen, which would generate trouble reports and possibly disturb other calls in the system due to co-channel interference. Although a single ESN may have an infinite number of telephone numbers, each telephone number can have at most one ESN. This is an immutable part of the design of the AMPS system. Although the moderator suggests that the way around this would be to convince the cellular carrier to not do its usual serial number check as part of handling his calls, this has all the problems mentioned above, plus the problem of making the roamer validation system not work. Mr. Cantor would be subject to fraud from anyone anywhere in the U.S. or Canada who knew that his phone number had no ESN. The only option is to have a portable which is carried from car to car. Some portables, especially NEC and Motorola portables, are designed such that you can install a complete set of 3 watt electronics in each car which are activated only when the portable, which contains the number and ESN, are plugged into the socket in the car. This way, someone who drives two cars can have a single phone number for each car. Or, better yet, two people who share two cars can each have their own portable and their own number will always be active in the car they are driving. /john [Moderator's Note: Actually, Mr. Covert's suggestion, re use of portables, makes a lot of sense. There are so many varieties now, and the price has come down so much, it seems far more efficient to simply transfer a hand-held unit from one vehicle to another ... and carry it when you leave the vehicle, as I do. A couple portable units, combined with call-forwarding as needed should be adequate. PT]
rees@dabo.ifs.umich.edu (Jim Rees) (06/11/90)
In article <8827@accuvax.nwu.edu>, "John R. Covert 09-Jun-1990 1015" <covert@covert.enet.dec.com> writes: > >A friend of mine wants to have two cellular telephones in two > >different cars with the same telephone number. Of course, he will use > >only one at a time. The telco won't set this up for him. > The only option is to have a portable which is carried from car to > car. What I envision is a smart-card that contains your ESN, phone number, and billing info. When you slide it in to any cell phone, that phone becomes your phone. It answers calls to your number and lets you make outgoing calls which then get billed to you. The same card could also be used at a payphone. You could have it demand a PIN for each use if you were security conscious. On a related subject, I hope that when European unity comes we can dispense with all those different phone cards and have one card that works anywhere on the continent. Unfortunately this doesn't seem very likely, since the cards all seem to be physically different from each other, at least the ones I've examined. Can anyone tell me how the British card works? On the French card you can see the electrical contacts, but the British one doesn't seem to have any. Is it done electromagnetically? Or with mirrors?
covert@covert.enet.dec.com (John R. Covert 12-Jun-1990 0939) (06/12/90)
>What I envision is a smart-card that contains your ESN, phone number, ...
For those of you who have read the description of the German C-Netz
system which I translated and posted to the Digest a year ago, this is
already known. That system provides exactly what you're suggesting.
Unfortunately, the AMPS protocol can't do what it really takes to make
this secure. The German system has two serial numbers -- one for the
smart card and one for the phone itself. If either the phone or the
card is stolen, it can be blocked from making further calls.
With the single ESN built into the AMPS protocol, if the smart card
contained the ESN, a stolen phone would have full market value. If
the phone contained the ESN, you would have to change your phone
number (and never reuse it, using up numbers permanently) if the card
were lost, stolen, or damaged.
Since the U.S. seems to be firmly wedded to the AMPS protocol, so much
so that we'll not be adopting the CCITT standard Group Special Mobile,
which would have allowed U.S. <-> Europe roaming, you won't see any
changes that would require protocol changes.
But _hopefully_ our system will continue to get cheaper, both in the
cost of phones, calls, and cell-site construction, such that smaller
and smaller pocket portables can be expected to operate well enough
that the smart-card idea won't ever be necessary. Why have a heavy 3
Watt phone when there's always a cell close enough to reach it with
600 mW or less?
/johnjohns@happy.uk.sun.com (John Slater) (06/14/90)
In article <8865@accuvax.nwu.edu>, rees@dabo.ifs.umich.edu (Jim Rees) writes: >Can anyone tell me how the British card works? On the French card you >can see the electrical contacts, but the British one doesn't seem to >have any. Is it done electromagnetically? Or with mirrors? I used to know this. I seem to remember it's got something to do with application of heat to the card. The card itself is read magnetically, but when a particular 10p unit has been used it is disabled either by a laser or by local heating. I may be totally wrong. I'm sure someone will correct me if I am. John Slater Sun Microsystems UK, Gatwick Office