Section: 5.4.1.3 Mobile Initiated Connection Only (MICO) mode
Content: A UE may indicate preference for MICO mode during Initial Registration or Mobility Registration Update procedure. The AMF, based on local configuration, Expected UE Behaviour and/or Network Configuration parameters if available from the UDM, UE indicated preferences, UE subscription information and network policies, or any combination of them, determines whether MICO mode is allowed for the UE and indicates it to the UE during Registration procedure. If NWDAF is deployed, the AMF may also use analytics on UE mobility and/or UE communication generated by NWDAF (see TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [86]) to decide MICO mode parameters. If the UE does not indicate preference for MICO mode during Registration procedure, the AMF shall not activate MICO mode for this UE. The UE and the AMF re- negotiate the MICO mode at every subsequent Registration procedure. When the UE is in CM-CONNECTED, the AMF may deactivate MICO mode by triggering Mobility Registration Update procedure through UE Configuration Update procedure as described in clause 4.2.4 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. The AMF assigns a registration area to the UE during the Registration procedure. When the AMF indicates MICO mode to a UE, the registration area is not constrained by paging area size. If the AMF serving area is the whole PLMN, based on local policy, and subscription information, may decide to provide an "all PLMN" registration area to the UE. In that case, re-registration to the same PLMN due to mobility does not apply. If Mobility Restrictions are applied to a UE in MICO mode, the AMF needs to allocate an Allowed Area/Non-Allowed Area to the UE as specified in clause 5.3.4.1. When the AMF indicates MICO mode to a UE, the AMF considers the UE always unreachable while the UE CM state in the AMF is CM-IDLE. The AMF rejects any request for downlink data delivery for UE in MICO mode and whose UE CM state in the AMF is CM-IDLE with an appropriate cause. For MT-SMS over NAS, the AMF notifies the SMSF that UE is not reachable, then the procedure of the unsuccessful Mobile terminating SMS delivery described in clause 4.13.3.9 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] is performed. The AMF also defers location services, etc. The UE in MICO mode is only reachable for mobile terminated data or signalling when the UE is in CM-CONNECTED. A UE in MICO mode need not listen to paging while in CM-IDLE. A UE in MICO mode may stop any access stratum procedures in CM-IDLE, until the UE initiates transition from CM-IDLE to CM-CONNECTED due to one of the following triggers: - A change in the UE (e.g. change in configuration) requires an update of its registration with the network. - Periodic registration timer expires. - MO data pending. - MO signalling pending (e.g. SM procedure initiated). If a registration area that is not the "all PLMN" registration area is allocated to a UE in MICO mode, then the UE determines if it is within the registration area or not when it has MO data or MO signalling, and the UE performs Mobility Registration Update before the UE initiates the MO data or MO signalling if it is not within the registration area. A UE initiating emergency service shall not indicate MICO preference during Registration procedure. When the MICO mode is already activated in the UE, the UE and AMF shall locally disable MICO mode after PDU Session Establishment procedure for Emergency Services is completed successfully. The UE and the AMF shall not enable MICO mode until the AMF accepts the use of MICO mode in the next registration procedure. To enable an emergency call back, the UE should wait for a UE implementation-specific duration of time before requesting the use of MICO mode after the release of the emergency PDU session. In order to enable power saving for MT reachability e.g. for Cellular IoT, enhancements to MICO mode are specified in clause 5.31.7: - MICO mode with Extended Connected Time. - MICO mode with Active Time. - MICO mode and Periodic Registration Timer Control.