BS-11 multidrop E1 status update

[Harald Welte]

Hi all,

On Tue, Aug 04, 2009 at 12:53:38AM +0200, Harald Welte wrote:
> 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.

The problem is now solved.  It seems that we need to create the BPORT1 object
on BTS-A, and configure both BPORT0 and BPORT1 into multi-drop mode.  Thanks
to Dieter for his help with that.

I can now see the TEI requests from BTS-B on the E1 link between BSC and BTS-A.

Karsten Keil of mISDN has offeres his help to provide a quick solution in
the hfcmulti driver where we would have two virtual mISDN cards on one physical
HFC-E1 device.  OpenBSC's mISDN input module then needs to be instantiated
twice, it simply looks exactly like the two BTS are connected to two different
E1 cards.

This is actually quite nice, since then the OpenBSC configuration does not
change at all, whether you have two BTS in star topology, using two HFC-E1
boards - or two BTS in multi-drop configuration using one HFC-E1 board.

> GSM 12.21 specifies a "CONNECT MULTI-DROP LINK" message, using which you can

This is not required at all.  It seems the BTS just passes all E1 frames from
BPORT1 to BPORT0, unless that very timeslot is used by the BTS itself.

So if BTS-A is the multi-drop BTS and it uses Timeslot 1 for signalling, all
data from BPORT1 (BTS-B) on Timeslot 1 is discarded.

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