Section: 5.5.2.2.6 Abnormal cases in the UE
Content: The following abnormal cases can be identified: a) Lower layer failure or release of the N1 NAS signalling connection before reception of DEREGISTRATION ACCEPT message. The de-registration procedure shall be aborted and the UE proceeds as follows: 1) if the de-registration procedure was performed due to disabling of 5GS services, the UE shall enter the 5GMM-NULL state; or 2) if the de-registration type "normal de-registration" was requested for reasons other than disabling of 5GS services, the UE shall enter the 5GMM-DEREGISTERED state. b) The lower layers indicate that the access attempt is barred. The UE shall not start the de-registration signalling procedure. The UE stays in the current serving cell and applies the normal cell reselection process. Receipt of the access barred indication shall not trigger the selection of a different core network type (EPC or 5GCN). The UE may perform a local de-registration either immediately or after an implementation-dependent time. The de-registration signalling procedure is started, if still needed, when the lower layers indicate that the barring is alleviated for the access category with which the access attempt was associated. ba) The lower layers indicate that: 1) access barring is applicable for all access categories except categories 0 and 2 and the access category with which the access attempt was associated is other than 0 and 2; or 2) access barring is applicable for all access categories except category 0 and the access category with which the access attempt was associated is other than 0. If the DEREGISTRATION REQUEST message has not been sent, the UE shall proceed as specified for case b. If the DEREGISTRATION REQUEST message has been sent, the UE shall proceed as specified for case a. c) T3521 timeout. If the de-registration procedure was performed based on conditions specified in 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [5] annex C, on the expiry of timer T3521 the de-registration procedure shall be aborted and the UE shall locally release the established N1 NAS signalling connection and enter the 5GMM-DEREGISTERED state. Otherwise, on the first four expiries of the timer, the UE shall retransmit the DEREGISTRATION REQUEST message and shall reset and restart timer T3521. On the fifth expiry of timer T3521, the de-registration procedure shall be aborted and the UE proceeds as follows: 1) if the de-registration procedure was performed due to disabling of 5GS services, the UE shall enter the 5GMM-NULL state; or 2) if the de-registration type "normal de-registration" was requested for reasons other than disabling of 5GS services, the UE shall enter the 5GMM-DEREGISTERED state. d) De-registration procedure collision. De-registration containing de-registration type "switch off": - If the UE receives a DEREGISTRATION REQUEST message before the UE-initiated de-registration procedure has been completed, this message shall be ignored and the UE-initiated de-registration procedure shall continue. Otherwise: - If the UE receives a DEREGISTRATION REQUEST message before the UE-initiated de-registration procedure has been completed, it shall treat the message as specified in subclause 5.5.2.3.2 with the following modification: - If the DEREGISTRATION REQUEST message received by the UE contains de-registration type "re-registration required", and the UE-initiated de-registration procedure is with de-registration type "normal de-registration": - If the access type included in the DEREGISTRATION REQUEST message sent by the UE is same as access type sent by the network, the UE need not initiate the registration procedure for initial registration; or - If the access type included in the DEREGISTRATION REQUEST message sent by the UE is not same as access type sent by the network, the UE shall initiate the registration procedure for initial registration for the access type not indicated in the DEREGISTRATION REQUEST message sent by the UE but indicated by the network. e) De-registration and 5GMM common procedure collision. De-registration containing de-registration type "switch off": - If the UE receives a message used in a 5GMM common procedure before the de-registration procedure has been completed, this message shall be ignored and the de-registration procedure shall continue. Otherwise: - If the UE receives a message used in a 5GMM common procedure before the de-registration procedure has been completed, both the 5GMM common procedure and the de-registration procedure shall continue; or - If the UE receives a DL NAS TRANSPORT message containing payload container type "Service-level-AA container" before the de-registration procedure has been completed, this message shall be ignored and the de-registration procedure shall continue. f) Change in the current TAI. If that the current TAI is not in the stored TAI list before the UE-initiated de-registration procedure is completed, the UE proceeds as follows: 1) if the de-registration procedure was initiated for reasons other than removal of the USIM, the UE is to be switched off or due to the last Tsor-cm timer expiry or stopped (see 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [5]), the de-registration procedure shall be aborted and re-initiated after successfully performing a registration procedure for mobility or periodic update used for mobility (i.e. the 5GS registration type IE set to "mobility registration updating" in the REGISTRATION REQUEST message); or 2) if the de-registration procedure was initiated due to removal of the USIM or the UE is to be switched off or due to the last Tsor-cm timer expiry or stopped (see 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [5]), the UE shall abort the de-registration procedure, perform a local de-registration and enter the state 5GMM-DEREGISTERED. g) Transmission failure of DEREGISTRATION REQUEST message indication with change in the current TAI. If the current TAI is not in the TAI list, the UE proceeds as follows: 1) if the de-registration procedure was initiated for reasons other than removal of the USIM ,the UE is to be switched off or due to the last Tsor-cm timer expiry or stopped (see 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [5]), the de-registration procedure shall be aborted and re-initiated after successfully performing a registration procedure for mobility or periodic update; or 2) if the de-registration procedure was initiated due to removal of the USIM or the UE is to be switched off or due to the last Tsor-cm timer expiry or stopped (see 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [5]), the UE shall abort the de-registration procedure, perform a local de-registration and enter the state 5GMM-DEREGISTERED. If the current TAI is still part of the TAI list, the UE shall restart the de-registration procedure. h) Transmission failure of DEREGISTRATION REQUEST message indication without change in the current TAI. The UE shall restart the de-registration procedure. i) The lower layers indicate that the RRC connection has been suspended. De-registration containing de-registration type "switch off": - The UE may perform a local de-registration either immediately or after an implementation-dependent time. Otherwise: - The UE shall wait for an implementation-dependent time and shall restart the de-registration procedure, if still needed, upon expiry of the implementation-dependent time. For the cases a, f, g and i: - Timer T3521 shall be stopped if still running.