Section: 5.6.1.8 Abnormal cases on the network side
Content: The following abnormal cases can be identified: a) Lower layer failure. If a lower layer failure occurs before a SERVICE REJECT message has been sent to the UE or the service request procedure has been completed by the AMF, the AMF enters/stays in 5GMM-IDLE. b) Protocol error. If the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message is received with a protocol error, the AMF shall return a SERVICE REJECT message with one of the following 5GMM cause values: #96 invalid mandatory information; #99 information element non-existent or not implemented; #100 conditional IE error; or #111 protocol error, unspecified. The AMF stays in the current 5GMM mode. c) More than one SERVICE REQUEST message or CONTROL PLANE SERVICE REQUEST message received before the procedure has been completed (i.e., before SERVICE REJECT message has been sent or service request procedure has been completed). - If one or more of the information elements in the SERVICE REQUEST message or CONTROL PLANE SERVICE REQUEST message differs from the ones received within the previous SERVICE REQUEST message or CONTROL PLANE SERVICE REQUEST message, the previously initiated service request procedure shall be aborted, and the new service request procedure shall be progressed; - If the information elements do not differ, then the AMF shall continue with the previous service request procedure and shall not treat any further this SERVICE REQUEST message or this CONTROL PLANE SERVICE REQUEST message. d) REGISTRATION REQUEST message received with "initial registration" or "emergency registration" in the 5GS registration type IE before a SERVICE REJECT message has been sent or the service request procedure has been completed. If a REGISTRATION REQUEST message with "initial registration" or "emergency registration" in the 5GS registration type IE is received and the service request procedure has not been completed or a SERVICE REJECT message has not been sent, the AMF may initiate the 5GMM common procedures, e.g. the primary authentication and key agreement procedure. The AMF may e.g. after a successful primary authentication and key agreement procedure execution, abort the service request procedure, delete the 5GMM context, indicate towards the SMF that the 5GMM context has been deleted and progress the new REGISTRATION REQUEST message. e) REGISTRATION REQUEST message received with "mobility registration updating" or "periodic registration updating" in the 5GS registration type IE received before the service request procedure has been completed or a SERVICE REJECT message has been sent. If a REGISTRATION REQUEST message with "mobility registration updating" or "periodic registration updating" in the 5GS registration type IE is received and the service request procedure has not been completed or a SERVICE REJECT message has not been sent, the AMF may initiate the 5GMM common procedures, e.g. the primary authentication and key agreement procedure. The AMF may e.g. after a successful primary authentication and key agreement procedure execution, abort the service request procedure and progress the new REGISTRATION REQUEST message. f) If a CONTROL PLANE SERVICE REQUEST message with Control plane service type indicating "mobile originating request" is received after the AMF initiated a paging procedure, the AMF shall treat this CONTROL PLANE SERVICE REQUEST as a paging response and handle the message according to subclauses 5.6.1.4 and 5.6.1.5. g) CONTROL PLANE SERVICE REQUEST message received with the Data type field indicates "control plane user data" in the CIoT small data container IE or received with Payload container type IE set to "CIoT user data container" and: 1) the AMF does not have a PDU session routing context for the PDU session ID and the UE; or 2) the AMF unsuccessfully attempted to forward the user data container and the PDU session ID, then the AMF may send back to the UE the CIoT user data container or control plane user data which was not forwarded as specified in subclause 5.4.5.3.1 case l1) or case l2). h) Based on operator policy, if the service request from a UE not supporting CAG is rejected due to CAG restrictions, the network shall reject the service request with a 5GMM cause value other than the 5GMM cause #76 (Not authorized for this CAG or authorized for CAG cells only). NOTE: 5GMM cause #7 (5GS services not allowed), 5GMM cause #11 (PLMN not allowed), 5GMM cause #27 (N1 mode not allowed), 5GMM cause #73 (Serving network not authorized) can be used depending on the subscription of the UE and whether the UE roams or not. i) CIoT user data received for a PDU session ID which is inactive in the network. If a CONTROL PLANE SERVICE REQUEST message is received with CIoT user data for a PDU session that is inactive in the network, the AMF shall discard the CIoT user data. The AMF shall send the SERVICE ACCEPT message and indicate that this PDU session ID is inactive using the PDU session status IE.