Hi Harald,
Have some good news.
I managed to bootstrap the UltraSite to on air, what I did was this:
https://github.com/dchard/osmo-bsc/commit/9be89196930f72f4f19d6c0bf512d68bda...
Just moved the RSL bootstrap to the NOKIA_MSG_CONF_COMPLETE part so Osmo-BSC waits for it to start the bootstrap. I was not able to test it with a call yet, but the site was on air and the phones where able to find it. Of course I am not sure how this affects possible error or exception handling.
I have no idea how this affects MetroSite or Insite, but hopefully their protocol stack is not that different and this can be a generic solution.
I also fixed a typo in the code:
https://github.com/dchard/osmo-bsc/commit/f3554f78985b339ea0d440ea38386c1d57...
Any and all input are welcome.
Regards, Csaba