[Catchercatcher] (no subject)

Luca Melette luca at srlabs.de
Fri Jan 6 15:55:57 CET 2012


Hello,
 
> I just tried your patch after viewing your presentation on 28c3. I'm
> wondering because I always get the "red" status and I dont have a
> clue why. Your application was run in a resedential area in Berlin on
> different days. See the attached output from the catcher cather
> application.

This is a known issue, given by the cell selection instability.
Since we consider "multiple LAC change" a big problem, you can see here:

>   cell monitoring
>     camped:    0
>     MCC:       610 (610, 0)
>     MNC:       31 (31, 0)
>     LAC:       213 (213, 13)
>     CID:       [removed]

(LAC change count is 13)

that your osmocom mobile is jumping many times from one cell to another,
based on signal reception, making our monitoring code show a RED flag.
Your "problem" is to be in the middle of different LACs, and there is no
single cell with "very good signal". For now, you can fix this, allowing
the osmocom mobile to just stay on particular frequencies of same LAC.
See the file osmocom-bb/src/host/layer23/src/mobile/gsm322.c

#if 1
        /* set supported frequencies in cell selection list */
        for (i = 0; i <= 1023+299; i++)
                if ((ms->settings.freq_map[i >> 3] & (1 << (i & 7))))
                        cs->list[i].flags |= GSM322_CS_FLAG_SUPPORT;
#else
        cs->list[688].flags |= GSM322_CS_FLAG_SUPPORT;
#endif

the "#if 1" and the number 688 can be changed to "#if 0" and the ARFCN
you prefer to lock the mobile to a specific frequency.

This problem will be fixed in a proper way soon,
and the MCC/MNC parsing too.

Cheers,

LM


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