MDL-Error in case of OsmocomBB+OpenBTS
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.
> > 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.
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