Henry VIII wrote:

> John, that was extremely helpful. Thank you very much.
>
> One final question, that I now realize I should have asked
> earlier but didn't think it would be an issue.
>
> The purpose of obtaining the cell ID is so that we can
> determine approximate location of the tower and our client
> connected to it. I was just told, however, that the networks
> keep tower locations secret. If that's true we would be
> unable to determine tower location even if we have the cell
> ID. Do you know if this is the case?

For the USA, I don't know if you can look up that info anywhere.

If you're working in a limited area, some GSM devices can help
you find cell locations for yourself. I have Siemens phones,
and Wavecom and Falcom (Wavecom engine) modems which let me
read TA (timing advance). This will give distance to the cell
with an accuracy of about 550 metres. Do some intensive
automated logging with GPS correlation from a moving device,
and you can quickly build up a good picture of where the cells
are.

Here's a Wavecom modem, using "AT+CREG=2" to tell me about cell
ID changes, and "AT+CCED=1,4" (a Wavecom proprietary command)
to tell me the last-negotiated TA value:

+CREG: 1,"1030","639E"

AT+CCED=1,4
OK

+CCED: 8

TA = 8, so I'm about 4 to 4.5 km from this cell.

Now I'll do a free "supplementary services" command to force the
modem to interact with the network. This automatically
refreshes the TA value (the distance to the cell).

AT+CLIP?
+CLIP: 0,1

OK

I didn't get a fresh "+CCED:" unsolicited result, so the TA
value remains at 8 (valid TA range is 0 through 63).

+CREG: 1,"1030","1401"

We've had a change of serving cell, so I'll do:

AT+CLIP?
+CLIP: 0,1

OK

and get

+CCED: 4

discovering from this that this new cell is about 2 km away.

Unfortunately, there isn't a GSM standard command for reading
TA, so you're reliant on your device manufacturer providing
one. On the Siemens phone, I use a variant of the Siemens
proprietary "AT^SSTK" command.

John