In some implementations, a method implemented in a first NF may include receiving WTRU context information from a second NF during a PDU session establishment procedure or a PDU session modification procedure, where the first information includes an identifier of a third NF. The method may include storing the first information associated with the PDU session of a WTRU, the PDU session corresponding to the PDU session establishment procedure or the PDU session modification procedure. The method may include receiving a DL data notification and at least one of a plurality of second information from the third NF, or receiving a WTRU context update request from the second NF, and determining a state of the WTRU based on at least one of the DL data notification, the plurality of second information, or the WTRU context update request, the state of the WTRU is one of: reachable, unreachable, connected or idle.