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Harald Welte laforge at gnumonks.orgHi all,
based on some more traces taken from a different Racal 6113 in RBS2000 mode,
there is a consistent observation:
> 1) the BSC applies some magic pattern (0xaa / 0xff)
> 2) the BSC establishes the LAPD session for OML TEI/SAPI
> 3) there is no L2ML, contrary to lots of Ericsson Abis documentation
> that you can find online.
The 0xAA /0xFF pattern is only applied once at the very start-up of the
6113. After that, the 6113 loops in sending SABM (SAPI=62/TEI=62)
messages in a lot of 0x7E LAPD idle pattern.
So my assumption is that the initial 0xAA / 0xFF is more like an artefact
of the 6113 starting up or initializing its A-bis timeslots, whereas the
repeated SABM messages are what the BTS/RBS locks onto.
However, using a small demo program (rbs_sabm.c) sending the exact same
SABM messages (utilizing the in-kernel DAHDI HDLC in dslot=1) does not
trigger any response from the RBS. The RBS just simply continues to send
its 0x7F pattern on all timeslots.
The physical connection is definitely fine, i.e. if we enable TNOM on TS 24
of the RBS, we can clearly see valid HDLC traffic on TS24 - but of course
only for this TNOM and not for OML.
Also, if the RBS boots, the 0x7F pattern disappears for some time.
I'm right now really out of ideas. Applying the 0xAA / 0xFF pattern at the
very beginning is difficult using any standard DAHDI/mISDN HDLC implementation,
as you can either switch the line into raw mode and then transmit that pattern,
or switch into d-channel mode where the driver will do the HDLC framing but
generate the default 0x7E idle pattern only. And as indicated, I really don't
believe it will make any difference, as it only happens on 6113 start, but
not during the lopp while it waits for the RBS connection to establish.
Regards,
Harald
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
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