MDL-Error in case of OsmocomBB+OpenBTS

Kurtis Heimerl kheimerl at cs.berkeley.edu
Tue Jan 8 14:51:56 UTC 2013


Anything OpenBTS is doing wrong?

On Tuesday, January 8, 2013, Pavel Baturko wrote:

> Thanks for explanations and fast fix! It seems that now all works as
> should be.
>
> Pavel
>
> On Tue, Jan 8, 2013 at 12:58 PM, Sylvain Munaut <246tnt at gmail.com<javascript:_e({}, 'cvml', '246tnt at gmail.com');>
> > wrote:
>
>> The fix Andreas just pushed is what I suspected: A missing 'return'
>> that made the "ignore" casei, not really ignored.
>>
>> What seems to happen is:
>>  - We respond to the assignement a bit fast it seems and OpenBTS
>> doesn't see the first SABM at all (not in the OpenBTS trace at all)
>>  - When OpenBTS sees the SABM, it responds with the UA frame
>>  - OpenBTS doesn't send a new frame until quite a bit later, which
>> means the UA frame is resent several times by OpenBTS transceiver
>> application using it's filling table (which is why we see only 1 UA
>> frame in OpenBTS trace but multiple of them in the OsmocomBB trace)
>>  - OsmocomBB had a bug where it was supposed to ignore the extraneous
>> UA frame but instead was dropping the connection because of a missing
>> "return" inside the switch statement.
>>
>> Cheers,
>>
>>     Sylvain
>>
>
>
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