The invention relates to a signaling method for GSM/GPRS communication systems. The status of a core interface between two core subnetworks is measured in the core network (S2), preferably through a keep-alive mechanism (S1). A status indication message is then sent to the radio network (S3). In this way, the BSS becomes aware of possible interface problems and failures, and can take appropriate actions, such as changing the network operating settings related to the NOM and/or allocated channel types (S4). The invention enables secure operation of NOM-I systems with P-channels irrespective of the Gs interface status.