5.5.1.3.8 Abnormal cases on the network side

The following abnormal cases can be identified:

• Lower layer failure

If a lower layer failure occurs before the message REGISTRATION COMPLETE has been received from the UE and timer T3550 is running, the AMF shall abort the procedure, enter 5GMM-IDLE mode.

If a new 5G-GUTI was assigned to the UE in the REGISTRATION ACCEPT message, the AMF shall consider both, the old and new 5G-GUTIs as valid until the old 5G-GUTI can be considered as invalid by the AMF. If a new TAI list was provided in the REGISTRATION ACCEPT message, both the old and new TAI lists shall also be considered valid until the old TAI list can be considered invalid by the AMF. If the old 5G-GUTI was allocated by an AMF other than the current AMF, the current AMF does not need to retain the old 5G-GUTI.

If the REGISTRATION ACCEPT message includes:

• Negotiated PEIPS assistance information IE:
• containing a new PEIPS assistance information and the UE is previously assigned a different PEIPS assistance information then, the AMF shall consider both, the old and new PEIPS assistance information as valid until the old PEIPS assistance information can be considered as invalid by the AMF; or

NOTE 0: If the UE was not previously assigned a PEIPS assistance information by the AMF, then AMF informs RAN about the new PEIPS assistance information, i.e. paging subgroup ID and it is up to RAN how to handle the old information at RAN and new information from AMF so that the paging is not missed.

• containing no PEIPS assistance information, then the AMF shall delete any old PEIPS assistance information stored in the 5GMM context of the UE.
• Negotiated WUS assistance information IE:
• containing a new UE paging probability information value and the UE is previously assigned a different UE paging probability information value then, the AMF shall consider both, the old and new UE paging probability information values as valid until the old UE paging probability information value can be considered as invalid by the AMF; or
• containing no UE paging probability information value, then the AMF shall delete any old UE paging probability information value stored in the 5GMM context of the UE.
• Negotiated LP-WUSPS assistance information IE:
• containing a new LP-WUSPS assistance information and the UE is previously assigned a different LP-WUSPS assistance information then, the AMF shall consider both, the old and new LP-WUSPS assistance information as valid until the old LP-WUSPS assistance information can be considered as invalid by the AMF; or

NOTE 0A: If the UE was not previously assigned a LP-WUSPS assistance information by the AMF, then AMF informs RAN about the new LP-WUSPS assistance information, i.e. LP-WUSPS paging subgroup ID and it is up to RAN how to handle the old information at RAN and new information from AMF so that the paging is not missed.

• containing no LP-WUSPS assistance information, then the AMF shall delete any old LP-WUSPS assistance information stored in the 5GMM context of the UE.
• LP-WUS status IE containing a new LP-WUS status and the UE was previously assigned old LP-WUS status then the AMF shall consider both the old LP-WUS status and the new LP-WUS status as valid until the old LP-WUS status can be considered as invalid by the AMF.

If the REGISTRATION ACCEPT message does not include:

• Negotiated PEIPS assistance information IE, then the AMF shall delete any old LP-WUSPS assistance information stored in the 5GMM context of the UE;
• Negotiated WUS assistance information IE, then the AMF shall delete any old UE paging probability information value stored in the 5GMM context of the UE;
• Negotiated LP-WUSPS assistance information IE, then the AMF shall delete any old LP-WUSPS assistance information stored in the 5GMM context of the UE; and
• LP-WUS status IE then the AMF shall delete any old "LP-WUS disabled" stored in the 5GMM context of the UE.

During this period:

• if the new 5G-GUTI is used by the UE in a subsequent message, then:
• the AMF shall consider the old 5G-GUTI as invalid and, additionally, the old TAI list as invalid if a new TAI list was provided with the new 5G-GUTI in the REGISTRATION ACCEPT message;
• if the AMF assigns a new PEIPS assistance information to the UE in the Negotiated PEIPS assistance information IE in the REGISTRATION ACCEPT message, then, the AMF shall consider the new PEIPS assistance information in the Negotiated PEIPS assistance information IE as valid and the old PEIPS assistance information sent as part of old Negotiated PEIPS assistance information IE, if any, as invalid;

iii) if the AMF assigns a new UE paging probability information value in the Negotiated WUS assistance information IE to the UE in the REGISTRATION ACCEPT message, then, the AMF shall consider the new UE paging probability information value as valid and the old UE paging probability information value, if any, as invalid;

• if the AMF assigns a new LP-WUSPS assistance information to the UE in the Negotiated LP-WUSPS assistance information IE in the REGISTRATION ACCEPT message, then, the AMF shall consider the new LP-WUSPS assistance information in the Negotiated LP-WUSPS assistance information IE as valid and the old LP-WUSPS assistance information sent as part of old Negotiated LP-WUSPS assistance information IE, if any, as invalid; and
• if the AMF assigns a new LP-WUS status to the UE in the LP-WUS status IE in the REGISTRATION ACCEPT message then the AMF shall consider the new LP-WUS status in the LP-WUS status as valid and the old the LP-WUS status sent as part of old the LP-WUS status IE, if any, as invalid. If the new LP-WUS status is "LP-WUS disabled", the AMF shall store "LP-WUS disabled" in the 5GMM context of the UE. If the new LP-WUS status is "LP-WUS disabled", the AMF shall delete "LP-WUS disabled" in the 5GMM context of the UE, if any.
• if the old 5G-GUTI is used by the UE in a subsequent message, the AMF may use the identification procedure followed by a generic UE configuration update procedure.

If the AMF in the REGISTRATION ACCEPT message assigns a new PEIPS assistance information for NR paging subgrouping to the UE then, the AMF shall include the new PEIPS assistance information in the Updated PEIPS assistance information IE and initiate the generic UE configuration update procedure.

If the AMF in the REGISTRATION ACCEPT message assigns a new LP-WUSPS assistance information for LP-WUSPS paging to the UE then, the AMF shall include the new LP-WUSPS assistance information in the Updated LP-WUSPS assistance information IE and initiate the generic UE configuration update procedure; and

If the AMF in the REGISTRATION ACCEPT message assigns a new LP-WUS status to the UE then the AMF shall include the new LP-WUS status in the LP-WUS status IE and initiate the generic UE configuration update procedure; and

• if the UE needs to be paged:
• if in the REGISTRATION ACCEPT message a new Paging subgroup ID in the Negotiated PEIPS assistance information IE is assigned to the UE:
• that previously has no Paging subgroup ID assigned for NR paging subgrouping then, the AMF shall use the new Paging subgroup ID for paging the UE;
• that is same as the old Paging subgroup ID for NR paging subgrouping then, the AMF shall use the same Paging subgroup ID for paging the UE; or
• that is different than the old Paging subgroup ID for NR paging subgrouping then, the AMF may first use the old Paging subgroup ID for NR paging subgrouping followed by the new Paging subgroup ID for NR paging subgrouping for paging the UE.

i1) if in the REGISTRATION ACCEPT message a new LP-WUSPS paging subgroup ID in the Negotiated LP-WUSPS assistance information IE is assigned to the UE:

• that previously has no LP-WUSPS paging subgroup ID assigned for LP-WUSPS paging then, the AMF shall use the new LP-WUSPS paging subgroup ID for paging the UE;
• that is same as the old LP-WUSPS paging subgroup ID for LP-WUSPS paging then, the AMF shall use the same LP-WUSPS paging subgroup ID for paging the UE; or
• that is different than the old LP-WUSPS paging subgroup ID for LP-WUSPS paging then, the AMF may first use the old LP-WUSPS paging subgroup ID for LP-WUSPS paging followed by the new LP-WUSPS paging subgroup ID for LP-WUSPS paging the UE.

i2) if in the REGISTRATION ACCEPT message a new LP-WUS status in the LP-WUS status IE is assigned to the UE:

• that is same as the old LP-WUS status then the AMF shall use the same LP-WUS status for paging the UE; or
• that is different than the old LP-WUS status then the AMF may first use the old LP-WUS status for paging the UE followed by the new LP-WUS status for paging the UE.
• if in the REGISTRATION ACCEPT message a new UE paging probability information value in the Negotiated WUS assistance information IE is assigned to the UE:
• that previously has no UE paging probability information value assigned then, the AMF shall use the new UE paging probability information value for paging the UE;
• that is same as the old UE paging probability information value then, the AMF shall use the same UE paging probability information value for paging the UE; or
• that is different than the old UE paging probability information value then, the AMF may first use the old UE paging probability information value followed by the new UE paging probability information value for paging the UE.

iii) the AMF selects the 5G-GUTI and TAI list as follows:

• the AMF may first use the old 5G-S-TMSI from the old 5G-GUTI for paging within the area defined by the old TAI list for an implementation dependent number of paging attempts using the selected Paging subgroup ID for NR paging, the selected LP-WUSPS paging subgroup ID for LP-WUSPS paging, the selected UE paging probability information value in the WUS assistance information IE, or the selected LP-WUS status. If a new TAI list was provided in the REGISTRATION ACCEPT message, the new TAI list should also be used for paging. Upon response from the UE, the AMF may initiate the generic UE configuration update procedure. If the response is received from a tracking area within the old and new TAI list, the network shall initiate the generic UE configuration update procedure. If in the REGISTRATION ACCEPT message a new PEIPS assistance information for NR paging was assigned to the UE that is different than the old PEIPS assistance information for NR paging, a new LP-WUSPS assistance information for LP-WUS paging was assigned to the UE that is different than the old LP-WUSPS assistance information for LP-WUS paging, or a new LP-WUS status was assigned to the UE that is different than the old LP-WUS status, then the network shall initiate the generic UE configuration update procedure; and
• if no response is received to the paging attempts using the old 5G-S-TMSI from the old 5G-GUTI and the old Paging subgroup ID for NR paging, the old LP-WUS paging subgroup ID for LP-WUS paging or the old UE paging probability information value in the WUS assistance information IE, the AMF may use the new 5G-S-TMSI from the new 5G-GUTI and the new Paging subgroup ID for NR paging, the new LP-WUS paging subgroup ID for LP-WUS paging, the new UE paging probability information value in the WUS assistance information IE, or the new LP-WUS status for paging, if any, for paging, for an implementation dependent number of paging attempts. In this case, if a new TAI list was provided with the new 5G-GUTI in the REGISTRATION ACCEPT message, the new TAI list shall be used instead of the old TAI list.
• Protocol error.

If the REGISTRATION REQUEST message has been received with a protocol error, the AMF shall return a REGISTRATION 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.

• T3550 time out.

On the first expiry of the timer, the AMF shall retransmit the REGISTRATION ACCEPT message and shall reset and restart timer T3550. The retransmission is performed four times, i.e. on the fifth expiry of timer T3550, the registration procedure for mobility and periodic registration update procedure is aborted.

During this period the AMF acts as described for case a) above.

• REGISTRATION REQUEST with 5GS registration type IE set to "mobility registration updating" or "periodic registration updating" received after the REGISTRATION ACCEPT message has been sent and before the REGISTRATION COMPLETE message is received, if the REGISTRATION COMPLETE message is expected.
• If one or more of the information elements in the REGISTRATION REQUEST message differ from the ones received within the previous REGISTRATION REQUEST message, the previously initiated registration procedure for mobility and periodic registration update shall be aborted if the REGISTRATION COMPLETE message has not been received and the new registration procedure for mobility and periodic registration update shall be progressed; or
• if the information elements do not differ, then the REGISTRATION ACCEPT message shall be resent and timer T3550 shall be restarted. In that case, the retransmission counter related to timer T3550 is not incremented.
• More than one REGISTRATION REQUEST message with 5GS registration type IE set to "mobility registration updating" or "periodic registration updating" received and neither REGISTRATION ACCEPT message nor REGISTRATION REJECT message has been sent.
• If one or more of the information elements in the REGISTRATION REQUEST message differs from the ones received within the previous REGISTRATION REQUEST message, the previously initiated registration procedure for mobility and periodic registration update shall be aborted and the new registration procedure for mobility and periodic registration update shall be progressed; or
• if the information elements do not differ, then the network shall continue with the previous registration procedure for mobility and periodic registration update and shall not treat any further this REGISTRATION REQUEST message.
• Lower layers indication of non-delivered NAS PDU due to handover.

If the REGISTRATION ACCEPT message or REGISTRATION 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 REGISTRATION ACCEPT message or REGISTRATION REJECT message. If a failure of the handover procedure is reported by the lower layer and the N1 NAS signalling connection exists, the AMF shall retransmit the REGISTRATION ACCEPT message or REGISTRATION REJECT message.

• DEREGISTRATION REQUEST message received before REGISTRATION COMPLETE message is received, if the REGISTRATION COMPLETE message is expected.

If the De-registration type IE is set to "switch off":

The AMF shall abort the signalling for the registration procedure for mobility and periodic registration update towards the UE and shall progress the de-registration procedure as described in clause 5.5.2.2.

NOTE 1: Internally in the AMF, before processing the de-registration request, the AMF can perform the necessary signalling procedures for the registration procedure for mobility and periodic registration update before progressing the de-registration procedure.

If the De-registration type IE is set to other type than "switch off":

The AMF shall proceed with registration procedure for mobility and periodic registration update and shall progress the de-registration procedure after successful completion of the registration procedure for mobility and periodic registration update.

• If the REGISTRATION REQUEST message with 5GS registration type IE indicating "periodic registration updating" is received by the new AMF which does not have the 5GMM context data related to the subscription, the new AMF may send the REGISTRATION REJECT message with 5GMM cause #10 "implicitly de-registered".
• Based on operator policy, if the mobility and periodic registration update request from a UE not supporting CAG is rejected due to CAG restrictions, the network shall reject the mobility and periodic registration update request with a 5GMM cause value other than the 5GMM cause #76 (Not authorized for this CAG or authorized for CAG cells only).

NOTE 2: 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.