Core Network 5G Terminal MM (Mobility Management) Capabilities

MM (Mobility Management) is a key system in wireless networks for handling terminal (UE) mobility; in the 5G service-based architecture (SBA), it is handled by the AMF (Access and Mobility Management Function) unit to support ultra-high-speed, low-latency services; the 3GPP definition of 5GC handling of terminal (UE) mobility is as follows:

I. Core Network Capabilities In the 5G system, the core network capabilities of the terminal (UE) are divided into: S1 UE network capabilities (mainly used for E-UTRAN access-related core network parameters) and UE 5GMM core network capabilities (mainly including other UE capabilities related to 5GCN or EPS interworking); TS 24.501 [47] defines and includes non-radio-related capabilities (such as NAS security algorithms), where:

• S1 UE network capabilities are transmitted between all CN nodes, including AMF to AMF, AMF to MME, MME to MME, and MME to AMF handovers.
• UE 5GMM core network capabilities are only transmitted during AMF to AMF handovers.

II. AMF and MM To ensure that the UE MM core network capability information stored in the AMF remains up-to-date, such as when the USIM is moved to another device when out of coverage, and the original device does not send a detach message, and in the case of cross-RAT registration area updates, the UE should send the UE MM core network capability information to the AMF via NAS messages during initial registration and mobility registration update processes.

• The AMF should always store the latest UE MM core network capability information received from the UE; when the UE provides UE MM core network capabilities through registration signaling, any UE MM core network capability information received by the AMF from the old AMF/MME will be replaced.
• If the UE's MM core network capability information changes (whether in CM-CONNECTED state or CM-IDLE state), the UE should perform a mobility registration update process the next time it returns to NG-RAN coverage (see clause 4.2.2 of TS 23.502 [3]).

III. MM Capabilities of 5G Terminals include:

• Attaching to EPC with request type "handover" in the PDN connection request message (see clause 5.3.2.1 of TS 23.401 [26]);
• EPC NAS;
• Sending SMS via NAS;
• LCS;
• 5G SRVCC from NG-RAN to UTRAN (as described in TS 23.216 [88]);
• Radio Capability Signalling Optimization (RACS);
• Network slice-specific authentication and authorization;
• Receiving WUS assistance information (E-UTRA) - see clause 5.4.9;
• Paging subgroup support indication (NR) - see clause 5.4.12;
• CAG - see clause 5.30.3.3;
• Subscription-based network slice simultaneous registration restriction - see clause 5.15.12;
• NSAG support - see clause 5.15.14;
• Minimizing Service Interruption (MINT) - clause 5.40.

IV. Multi-SIM Card Scenario: If a UE operates two or more USIMs and supports and intends to use one or more multi-USIM functions in a PLMN (see clause 5.38), the UE shall indicate its support for these one or more multi-USIM functions in the UE 5GMM core network capabilities for that USIM in that PLMN and include the following indications:

• Support for connection release;
• Support for voice service paging cause indication;
• Support for rejecting paging requests;
• Support for paging restriction;

Otherwise, a UE with multi-USIM capabilities but not intending to use them shall not indicate support for these one or more multi-USIM functions.