[Catchercatcher] (no subject)

Karsten Nohl nohl at virginia.edu
Fri Jan 6 17:49:03 CET 2012


On Jan 6, 2012, at 15:55 , Luca Melette wrote:

> 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:

Thanks for reporting the two instances were this caused problems.
The severity and definition of 'multiple LAC changes' will be changed to:
'multiple different LACs' (ie, not just alternating between two)
'red flag' -> 'yellow flag'

Thanks again,

     -Karsten

>>  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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