5G Terminal (UE) MICO Connection Mode

During the initial registration or mobility registration update process, the 5G terminal (UE) will initiate a connection with the network, which is the MICO (Mobile Initiated Connection Only) connection mode; where:

I. The MICO mode allows the AMF to determine whether to allow the UE to use MICO mode and indicate this to the UE during the registration process, based on local configuration, expected UE behavior and/or network configuration parameters (if available from the UDM), UE indicated preferences, UE subscription information, and network policies, or any combination thereof.

• If NWDAF is deployed, the AMF may also use UE mobility and/or UE communication analysis data generated by NWDAF (see TS 23.288 [86]) to determine MICO mode parameters.
• If the UE does not indicate its preference for MICO mode during the registration process, the AMF should not activate MICO mode for that UE.

II. The UE and AMF renegotiate the MICO mode during each subsequent registration process; when the UE is in the CM-CONNECTED state, the AMF can deactivate the MICO mode by triggering a mobility registration update process; this process is performed through the UE configuration update process as described in Section 4.2.4 of TS 23.502 [3]; where:

• During the registration process, the AMF assigns a registration area to the UE. When the AMF indicates that the UE is in MICO mode, the registration area is not limited by the paging area size. If the AMF's service area covers the entire PLMN, the AMF may decide to provide the UE with a "full PLMN" registration area based on local policies and user information. In this case, re-registration due to mobility within the same PLMN is not applicable. If mobility restrictions are applied to a UE in MICO mode, the AMF needs to assign an allowed area/disallowed area to the UE as specified in Section 5.3.4.1.
• When the AMF indicates MICO mode to the UE, if the UE's CM state in the AMF is CM-IDLE, the AMF always considers the UE unreachable.
• For a UE in MICO mode and whose CM state in the AMF is CM-IDLE, the AMF will reject any downlink data transmission requests and provide the corresponding rejection reason. For NAS-based MT-SMS, the AMF will notify the SMSF that the UE is unreachable and then execute the mobile terminal SMS sending failure handling procedure described in TS 23.502 [3, Section 4.13.3.9].

III. Delayed Location Services: The AMF will enable delayed location services, allowing mobile terminal data or signaling communication only for UEs in MICO mode and only when they are in the CM-CONNECTED state.

IV. CM-IDLE State: UEs in CM-IDLE state do not need to listen for paging. UEs in MICO mode can stop any access layer procedures in the CM-IDLE state until the UE initiates a transition from CM-IDLE to CM-CONNECTED due to one of the following trigger conditions:

• The UE undergoes a change (e.g., configuration change) requiring an update of its registration information in the network.
• The periodic registration timer expires.
• MO signaling is pending (e.g., an SM procedure has been initiated).

If the registration area assigned to a UE in MICO mode is not the "all PLMNs" registration area, the UE will determine whether it is within that registration area when it has MO data or MO signaling. If the UE is not within the registration area, before initiating MO data or MO signaling,

V. UE and Emergency Services: The UE will perform a mobility registration update; a UE initiating emergency services shall not indicate MICO preference during the registration process. When MICO mode is activated in the UE, the UE and AMF locally disable MICO mode after the successful completion of the emergency service PDU session establishment process. The UE and AMF shall not enable MICO mode until the AMF accepts the use of MICO mode during the next registration process. To enable emergency callback, the UE should wait for a UE implementation-specific duration after the emergency PDU session release before requesting the use of MICO mode.

VI. MT Mode: To achieve energy saving for mobile terminal (UE) MT reachability (e.g., for cellular IoT), enhancements to the MICO mode are specified in the following clauses:

MICO mode with extended connection time;

MICO mode with active time;

MICO mode with periodic registration timer control.