Nokia InSite multiple BTSs with OpenBSC

Dear Members, As I previously mentioned, I have two Nokia InSite BTS units that I want to set up for my university. One GSM900 and one GSM1800 unit, and I want to share some findings that can be useful for other users too. First, the informations about the DAHDI configuration at the end of the building page: http://openbsc.osmocom.org/trac/wiki/Building_OpenBSC It sais the following for system.conf: dchan=1 bchan=2-30 I wanted to point out that it is not necessary to define a dchan, because with BTSes this is not a traditional E1 line configuration where you share timeslots and you have to signal it via the traditional E1 signaling channel (dchan), because for every BTS there are dedicated timeslots for OMUSIG, TRXSIG and TCHs etc, that cannot be used by anybody else. And because we are not using that dchan, it is a waste of capacity to allocate it. My DAHDI system.conf looks like this: span=1,0,0,ccs,hdb3,crc4 bchan=1-31 and it works perfectly without a configured dchan (well its far from perfect but at least the problem is not with the E1 configuration). Because every BTS works like this, it would be wise the update that information. For T1 lines and other framing configurations (cas, ami etc.) it is the same. The second thing is that Nokia InSite units (probably others too) can be daisy chained. It is possible to share the first BTS units E1 connection for the daisy chained units with the integrated HDSL cross-connection interface. With this technique it is possible to share one E1 connection between 5 BTSes. But there is a slight problem. I figured out if the BTS is not connecting to the E1 directly, but via this HDSL interface, it needs more time before it can be configured via OML,RSL. So in bts_nokia_site.c the #DEFINE RESET_INTERVAL have to be raise from the current 15 seconds to at least 25 seconds, otherwise the unit is not going to came up. With this modification I was able to use the unity via this HDSL cross-connection interface. The third thing is multiple BTS operation. As I mentioned I want to use two InSite units with OpenBSC. But at the beginning of bts_nokie_site.c there is a big warning: I most certainly going to have problems with multi BTS operation. Despite the warning I tried with two units, and found an interesting thing: if I try to start the two units, only one of the two units are going to came up. But if I start the daisy chained unit first, then stop openbsc and immediately start openbsc again but now with the two unit config file, both BTSes are came up just fine, the phones can camp on both units. I don't know the real reason behind this behavior, but I have log and PCAP traces about the working and non-working scenarios. If someone interested in it I can share the results. Although a possible reason is that in bts_nokia_insite.c the shutdown routine is completely missing. It is not a good solution, but at least we should reset the BTS(es) and all the signalling channels in the shutdown state (like with BS11), until we figure out some proper way of shutting Nokia BTSes down. BR, Csaba