Hi Sipos,
Not sure if it is of help since I never used a Nokia BTS, but you could look at osmo_bsc_main.c inp_sig_cb() which is basically the one applying the config at least for osmo-bts types.
In there, have a look at: """ if (isd->link_type == E1INP_SIGN_RSL) { ... bootstrap_rsl(): } """
In there, the one preparing the BCCH info afair is gsm_bts_trx_set_system_infos().
For osmo-bts (ipaccess type) AFAIR the S_L_INP_TEI_UP event is triggered when the BSC accepts the TCP/IPA RSL conn from the BTS, which usually happens *after* the TRX has been configured (since basically we provide the osmo-bsc local IP address for RSL to the osmo-bts during TRX setup over OML). See bb_transc->mo.rsl_connect_sent and bb_transc->mo.rsl_connect_ack_received.
Not sure if osmo-bsc code to handle nokia bts is actually using any of the "new" nm_*_fsm.c FSMs to set up stuff, I guess it's not?
Regards,