Channel info

Bogdan Alecu b.alecu at
Sun Jan 30 17:20:28 UTC 2011

Hi Mad,
Thanks for explaining me this. The case of the TMSI is different from network to network: some operators change it for every x minutes, others after a powercycle (at least here). You say that gsm tries to avoid sending out IMSIs but still some are sent. If I would send an SMS to the phone - so it will get a paging request - I should see the IMSI also in that list?

--- On Sun, 1/30/11, mad at <mad at> wrote:

From: mad at <mad at>
Subject: Re: Channel info
To: "Bogdan Alecu" <b.alecu at>
Cc: baseband-devel at
Date: Sunday, January 30, 2011, 3:54 PM

On Sun, 30 Jan 2011 03:42:43 -0800 (PST), Bogdan Alecu wrote:
> Hello,
> I noticed that when I start the mobile application, after the phone
> chooses a specific channel I get different messages regarding IMSI
> saying that it's not for us. What are these messages? Phones that camp
> on this channel? If so, I tried turning off/on a phone from the same
> operator but I can't see my IMSI showing up.

These are paging requests for phones in your location area. As osmocombb
receives them and checks them for its own imsi/tmsi, it discards those
ones you observed.
The imsi of your other phone should not ever be seen on the paging channel as
gsm trys to avoid sending out imsis as much as possible. Instead the network
attaches a tmsi to the imsi on your phones first network login (location update)
and uses that from there on for addressing the phone. This tmsi is kept by
storing on the sim card even over powercycle.


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