On Sat, Nov 03, 2018 at 12:06:33PM +0000, Snehasish Kar wrote:
> I have read that silent-calls in GSM can be used to make a call to a target
> MS and listen to it

Not listen to it in terms of audio. You can't eavesdrop on an MS with a slient
call.

You *can* open a channel and receive measurement reports from it, so that you
see which other cells it sees at which receive levels, and how far it is from
the current cell (TA). From that you could derive its position.

The silent call has been one of the earliest features in Osmocom, but until
recently has been broken in osmo-msc. IIUC it is now fixed again in current
master, but might not be in a release yet.

There's also the APDU a.k.a. the RR App Info (I hope I got the names right),
which may or may not contain GPS positioning data that the MS is sending to the
core net.

In both cases the owner of the MS has no explicit idea that they are sharing
any details on their position.

~N