Embodiments include method performed at a network node of a communication network, as well as network nodes configured to perform such methods. These methods include selecting, for a terminal device, a protocol data unit session identity (PDU) session identifier (ID) from a group of PDU session IDs that are not allocated to the terminal device by the communication network. In some embodiments, the group of PDU session IDs are not selectable by terminal devices. In some embodiments, the group of PDU session IDs are exclusive of a second group of PDU session IDs that are selectable by terminal devices. In some embodiments, the PDU session ID may be selected based on an evolved packet system (EPS) bearer ID and one of various mappings.