5.6.1.8 Abnormal cases on the network side

The following abnormal cases can be identified:

• 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.

• 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.

• 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.
• 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.

• 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.

• 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 clauses 5.6.1.4 and 5.6.1.5.
• If a 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:
• the AMF does not have a PDU session routing context for the PDU session ID and the UE; or
• 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 clause 5.4.5.3.1 case l1).

g0) If a 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:

• the timer T3447 is running and the UE supports service gap control;
• the UE is not configured for high priority access in selected PLMN; and
• the current N1 NAS signalling connection was not triggered by paging;

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 clause 5.4.5.3.1 case l2).

g1) If a CONTROL PLANE SERVICE REQUEST message received with the Data type field indicates "SMS" in the CIoT small data container IE or received with the Payload container type IE set to "SMS" and:

• the AMF does not have an SMSF address associated with the UE;
• the AMF cannot forward the content of the Payload container IE to the SMSF associated with the SMSF address available in the AMF; or
• the AMF determines that the UE has registered to a PLMN via a satellite NG-RAN cell that is not allowed to operate at the present UE location;

then the AMF may discard the CIoT small data container IE or the Payload container IE.

g2) If a CONTROL PLANE SERVICE REQUEST message received with the Data type field indicates "Location services message container" in the CIoT small data container IE or received with the Payload container type IE set to "Location services message container" and:

• the Additional information IE is included in the CONTROL PLANE SERVICE REQUEST message and the AMF cannot forward the content of the Payload container IE to an LMF associated with the routing information included in the Additional information IE;
• the AMF determines that the UE has registered to a PLMN via a satellite NG-RAN cell that is not allowed to operate at the present UE location;
• the AMF determines that the payload container content is related to PRU and the UE has not a valid PRU subscription information; or
• any combination of bullets 1 to 3,

then the AMF may discard the CIoT small data container IE or the Payload container IE.

g3) If a CONTROL PLANE SERVICE REQUEST message received with:

• the Data type field indicates "SMS" or "Location services message container" in the CIoT small data container IE; or
• the Payload container type IE set to "SMS" or "Location services message container";

and:

• the timer T3447 is running and the UE supports service gap control;
• the UE is not configured for high priority access in selected PLMN; and
• the current N1 NAS signalling connection was not triggered by paging,

then the AMF may discard the CIoT small data container IE or the Payload container IE.

• 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.

• 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.

• Lower layers indication of non-delivered NAS PDU due to handover.

If the SERVICE ACCEPT message or SERVICE REJECT message could not be delivered due to an intra AMF handover and the target TA is included in the TAI list, then upon successful completion of the intra AMF handover the AMF shall retransmit the SERVICE ACCEPT message or SERVICE REJECT message. If a failure of handover procedure is reported by the lower layer and the N1 NAS signalling connection exists, the AMF shall retransmit the SERVICE ACCEPT message or SERVICE REJECT message.