Not an issue: trying to understand how gr-gsm works.

[Mortific]

Hello! I am trying to wrap my head around gr-gsm, GSM standards and how it works. Please delete this post if it is in the wrong place.

When scanning with with grgsm_scanner I get data about a certain BTS (ARFCN and a frequency amongst other things)

Q1: Is the detected frequency uplink or downlink for the BTS?

Of what I could find, with my limited programming skills and reading GSM standards, I would guess it is the downlink.

Q2: If it is the downlink, when is the IMSI-number transmitted from the BTS?

I have read a couple of different books on the subject and my head is still not any clearer. Of what I have found is that TIMSI is transmitted but not the IMSI on the downlink. If you have any references on the subject I would appricate them gladly.

Regards //Mort