Section: 4.9 Disabling and re-enabling of UE's NB-IoT capability
Content: If the UE supports disabling and re-enabling of UE's NB-IoT capability and the UE in NB-S1 mode is disabling the NB-IoT capability, it should proceed as follows: a) select E-UTRAN, or for the UE which supports CIoT EPS optimization select satellite E-UTRAN via "WB-E-UTRAN(LEO)", "WB-E-UTRAN(MEO)", or "WB-E-UTRAN(GEO)", of the registered PLMN or a PLMN from the list of equivalent PLMNs; b) if E-UTRAN, or for the UE which supports CIoT EPS optimization if satellite E-UTRAN via "WB-E-UTRAN(LEO)", "WB-E-UTRAN(MEO)", or "WB-E-UTRAN(GEO)", of the registered PLMN or a PLMN from the list of equivalent PLMNs cannot be found, select another RAT (GERAN, UTRAN, or NG-RAN if the UE has not disabled its N1 mode capability for 3GPP access as specified in 3GPP TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [54]) of the registered PLMN or a PLMN from the list of equivalent PLMNs; c) if another RAT of the registered PLMN or a PLMN from the list of equivalent PLMNs cannot be found, or the UE does not have a registered PLMN, then perform PLMN selection as specified in 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [6]. As an implementation option, instead of performing PLMN selection, the UE may select another RAT of the chosen PLMN; or d) if no other allowed PLMN and RAT combinations are available, then the UE may re-enable the NB-IoT capability and remain registered for EPS services in NB-IoT of the registered PLMN. If the UE chooses this option, then it may periodically attempt to select another PLMN and RAT combination that can provide non-EPS services. How this periodic scanning is done, is UE implementation dependent. If the NB-IoT capability is disabled, the UE shall re-enable the NB-IoT capability when: - performing a PLMN selection unless the UE has already re-enabled the NB-IoT capability when performing bullet c) or d) above; or - the UE powers off and powers on again or the USIM is removed. If the UE in NB-S1 mode receives an ATTACH REJECT or TRACKING AREA UPDATE REJECT message including both EMM cause #15 "no suitable cells in tracking area" and an Extended EMM cause IE with value "NB-IoT not allowed" after the UE requests access to the NB-IoT, in order to prevent unwanted cell reselection from GERAN, UTRAN, E-UTRAN or NG-RAN to NB-IoT, the UE may: - disable the NB-IoT capability: - indicate the access stratum layer(s) of disabling of the NB-IoT capability; and - memorize the identity of the PLMN where the NB-IoT capability was disabled and use that stored information in subsequent PLMN selections as specified in 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [6]. NOTE: The UE can only disable the NB-IoT capability when in EMM-IDLE mode. If the UE in NB-S1 mode is required to disable the NB-IoT capability and select E-UTRAN radio access technology, and the UE is in the EMM-CONNECTED mode, the UE shall locally release the established NAS signalling connection and enter the EMM-IDLE mode before selecting E-UTRAN radio access technology. As an implementation option, the UE may start a timer for enabling the NB-IoT capability. On expiry of this timer, the UE may enable the NB-IoT capability.