Hi Shawn!
This splits into a technical (what do do) and a commercial / use case
(why do that) discussion.
On the technical aspect:
> So the GSM module must provide some AT
> commands to access whatever you need in order to implement SIM access
> profile, right?
Well, that's exactly the question. GSM modules don't necessarily know
anything about Bluetooth, do they? So I wonder if *any* GSM module would
support these commands or if I need a specially equipped GSM module for
that. But you're right, looking up the respective spec from the
Bluetooth SIG would make sense.
On the use case aspect:
> Another idea would be to use a GSM module with an Asterisk server.
That's what I am looking for; among others.
> But then you could also buy VOIP termination service, to virtualize it
> completely... so how is it better to use GSM?
Not better, cheaper. In Germany everyone can buy a SIM card which will
make you pay 0,09 EUR / minute for calls terminating on any GSM phone in
Germany, no matter which of the 4 network operators that would be. With
some luck you can even buy a SIM which will make you pay only 0,05 EUR /
minute. But there is no VoIP termination service that charges less than
~ 0,20 EUR for terminating in the mobile networks.
The other aspect would be just the opposite: VoIP originating on the
mobile network. Say you want to receive calls to your GSM phone number
in country X while you are in country Y. So you might want to have a GSM
-> VoIP gateway.
But both is easily doable (I guess) with current FIC hardware, as none
of that usecases requires to use more than one SIM or required to remote
the SIM.
I am looking at virtualizing / remoting SIMs more for Dual-SIM,
Tripe-SIM, etc. scenarious, i.e. you have a SIM from your employer and
maybe one or more personal SIMs but you want to carry just one handset.
If you employer would be so nice to pay GPRS traffic for you, you'd use
his SIM in the phone and remotely access your personal SIM sitting back
home on your server over GPRS; for example.
One thing is for sure, though: If the network operators would offer a
bit more flexibility with certain things, all this would not be needed.
But they don't necessarily have any incentive to spoil their business,
do they?
Regards,
Torsten
Shawn Rutledge schrieb:
On Dec 14, 2007 8:04 AM, Torsten Schlabach <[EMAIL PROTECTED]> wrote:
There is for example somthing in Bluetooth called "SIM access profile"
which is a mean to share a SIM card over Bluetooth. This is used by some
built-in car phones (not to mix up with simple hands-free sets, which
just transmit the audio over the Bluetooth connection) which read the
SIM card of the mobile in your pocket when you enter the car.
I was looking at implementing whatever mechanism where I could host a
SIM card that I legally own on a server and communicate with that SIM
card over whatever network connection (WiFi if available, maybe UMTS,
Bluetooth, ...).
If it can be done via SIM access profile, it could also be done on a
server as you suggest. So the GSM module must provide some AT
commands to access whatever you need in order to implement SIM access
profile, right? They probably consider that as long as the card is
"live" (actually connected to a card reader) and the exchange of
information (challenge/response) is the same as it would be if the
card were physically connected to the radio that is using it, then the
security is preserved. The communications with the card are not
secret, but the key which the card stores is the secret, and the
communication stream does not reveal it.
So why don't you investigate how to do that? First figure out how to
implement SIM access profile (specs for that from the Bluetooth SIG
would probably explain how.) Then you have code which would work just
as well on a server that has a GSM module connected via serial line,
and a Bluetooth dongle for the SIM access. (You can buy a GSM module
from SparkFun for that, and probably connect it via one of those
DLP-232 USB-to-serial cables.) Then, maybe figure out how to do the
same communications with the SIM card, with a simple USB SIM card
reader, so that the extra GSM module is not required (since it's only
being used as a card reader, effectively).
But as I cannot hook the communication between the GSM modem and the SIM
card (which is some kind of serial line connection) I have no means of
doing that.
Not directly with existing FIC hardware, but you could get out your
spectrum analyzer and monitor the communications. But it's
cryptography... it's not meant to be easy to crack. But if you only
want to provide a "wireless extension cable" to the physical SIM,
that's already sanctioned.
Another idea would be to use a GSM module with an Asterisk server.
Then you could use that virtual phone from anywhere that you have
network access to reach the server. (But then you could also buy VOIP
termination service, to virtualize it completely... so how is it
better to use GSM?) If you wanted to use it remotely, without a
pre-existing network connection, it's a chicken/egg problem... you
need the network in order to access the SIM remotely, but you're not
going to have GPRS until you access the SIM.
