code: public static boolean isSystemBroadcast(final CEMI frame) {
  		if (frame.getMessageCode() == CEMILData.MC_LDATA_IND && frame instanceof CEMILData) {
  			final CEMILData ldata = (CEMILData) frame;
  			final KNXAddress dst = ldata.getDestination();
  			return ldata.isSystemBroadcast() && dst instanceof GroupAddress && dst.getRawAddress() == 0;
  		}
  		return false;
  	}
docs: with a secure APDU or sync.req/res, the SBC currently has to be checked at an upper layer