BS-11 multidrop E1 status update

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Harald Welte laforge at gnumonks.org
Mon Aug 3 22:53:38 UTC 2009


Hi!

I've been experimenting for the last couple of hours with two BS-11 in
a multi-drop configuration.

The connection looks like this:

HFC-E1 connects to BTS A Y01/Y02, just like normal.
BTS-A Y03/Y04 connect to BTS-B Y01/Y02.

BTS-A LI object is configured as multi-drop
BTS-B LI object is configured normal (star)

BTA-A is configured to use TEI 25 on TS 1 for OML (normal)
BTS-B is configured to use TEI 26 on TS 10 for OML (differnt)

If I put the MA-10 A-bis signal analyzer between BTS A and BTS, I can see
* that the E1 physical layer is up and there are no alarms
* BTS-B sends TEI requests on timeslot 10, as requested

however, there is no response.  Looking at TS 10 between BTS-A and BSC, 
I can see that there are no TEI requests or any other data.

GSM 12.21 specifies a "CONNECT MULTI-DROP LINK" message, using which you can
map two E1 timeslots on two interfaces to each other.  I've done this (mapping
port 0, TS 10 to port 1, TS 10) - but it seems the BS-11 does not support this
message.  The MA-10 also calls it an "unknown message".

I'm Sending this message to object class 0xa5 (SiemensHW) and to the LI object
in that class (object instance 7, 0, 0).  The BS-11 does not respond with ACK
and not with NACK. It seems it is simply ignored silently.

Does anyone have an idea how to proceed?  Or does anyone have an A-bis trace
from a working multi-drop configuration?

Thanks.
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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