h4. make sure your related BTS is configured to use a channel combination with CBCH

For using a combined CCCH with SDCCH/4 and CBCH you can use the following example snippet as part of osmo-bsc.cfg:
    

network

 bts 0

  trx 0

   timeslot 0

    phys_chan_config CCCH+SDCCH4+CBCH