5.30.3.4 Network and cell (re-)selection and access control

The following is assumed for network and cell selection and access control:

• The CAG cell shall broadcast information such that only UEs supporting CAG are accessing the cell (see TS 38.300 [27], TS 38.304 [50]);

NOTE 1: The above also implies that cells are either CAG cells or normal PLMN cells. For network sharing scenario between SNPN, PNI-NPN and PLMNs, please see clause 5.18.

• In order to prevent access to NPNs for authorized UE(s) in the case of network congestion/overload, existing mechanisms defined for Control Plane load control, congestion and overload control in clause 5.19 can be used, as well as the access control and barring functionality described in clause 5.2.5, or Unified Access Control using the access categories as defined in TS 24.501 [47] can be used.
• For aspects of automatic and manual network selection in relation to CAG, see TS 23.122 [17];
• For aspects related to cell (re-)selection, see TS 38.304 [50];
• If the UE is accessing a CAG cell and the corresponding entry of the Allowed CAG list configured on the UE is associated with time validity information, the UE may trigger cell reselection and/or network selection procedure if the evaluation of the time validity information changes.
• The Mobility Restrictions shall be able to restrict the UE's mobility according to the Allowed CAG list (if configured in the subscription) and include an indication whether the UE is only allowed to access 5GS via CAG cells (if configured in the subscription) as described in clause 5.30.3.3;
• The AMF shall update the Allowed CAG list in the Mobility Restrictions towards NG-RAN if the evaluation of the time validity information of an entry in the Allowed CAG list changes between true and false, unless the AMF releases the NAS signalling connection to the UE based on operator's policy if the evaluation of the validity condition changes from true to false.
• During transition from CM-IDLE to CM-CONNECTED and during Registration after connected mode mobility from E-UTRAN to NG-RAN as described in clause 4.11.1.2.2 of TS 23.502 [3]:
• The AMF shall verify whether UE access is allowed by Mobility Restrictions:

NOTE 2: It is assumed that the AMF is made aware of the supported CAG Identifier(s) of the CAG cell by the NG-RAN.

• If the UE is accessing the 5GS via a CAG cell and if at least one of the CAG Identifier(s) received from the NG-RAN is part of the UE's Allowed CAG list (for entries with time validity information if any, the evaluation of the condition is true), then the AMF accepts the NAS request;
• If the UE is accessing the 5GS via a CAG cell and if none of the CAG Identifier(s) received from the NG-RAN are part of the UE's Allowed CAG list (for entries with time validity information if any, the evaluation of the condition is true), then the AMF rejects the NAS request and the AMF should include CAG information in the NAS reject message. The AMF shall then release the NAS signalling connection for the UE by triggering the AN release procedure; and
• If the UE is accessing the 5GS via a non-CAG cell and the UE's subscription contains an indication that the UE is only allowed to access CAG cells, then the AMF rejects the NAS request and the AMF should include CAG information in the NAS reject message. The AMF shall then release the NAS signalling connection for the UE by triggering the AN release procedure.
• During transition from RRC_INACTIVE to RRC_CONNECTED state:
• When the UE initiates the RRC Resume procedure for RRC_INACTIVE to RRC_CONNECTED state transition in a CAG cell, NG-RAN shall reject the RRC Resume request from the UE if none of the CAG Identifiers supported by the CAG cell are part of the UE's Allowed CAG list according to the Mobility Restrictions received from the AMF or if no Allowed CAG list has been received from the AMF.
• When the UE initiates the RRC Resume procedure for RRC_INACTIVE to RRC_CONNECTED state transition in a non-CAG cell, NG-RAN shall reject the UE's Resume request if the UE is only allowed to access CAG cells according to the Mobility Restrictions received from the AMF.
• During connected mode mobility procedures within NG-RAN, i.e. handover procedures as described in clause 4.9.1 of TS 23.502 [3]:
• Source NG-RAN shall not handover the UE to a target NG-RAN node if the target is a CAG cell and none of the CAG Identifiers supported by the CAG cell are part of the UE's Allowed CAG list in the Mobility Restriction List or if no Allowed CAG list has been received from the AMF;
• Source NG-RAN shall not handover the UE to a non-CAG cell if the UE is only allowed to access CAG cells based on the Mobility Restriction List;
• If the target cell is a CAG cell, target NG-RAN shall reject the N2 based handover procedure if none of the CAG Identifiers supported by the CAG cell are part of the UE's Allowed CAG list in the Mobility Restriction List or if no Allowed CAG list has been received from the AMF;
• If the target cell is a non-CAG cell, target NG-RAN shall reject the N2 based handover procedure if the UE is only allowed to access CAG cells based on the Mobility Restriction List.
• Update of Mobility Restrictions:
• When the AMF receives the Nudm_SDM_Notification from the UDM and the AMF determines that the Allowed CAG list or the indication whether the UE is only allowed to access CAG cells have changed;
• The AMF shall update the Mobility Restrictions in the UE and NG-RAN accordingly under the conditions as described in clause 4.2.4.2 of TS 23.502 [3].

NOTE 3: When the UE is accessing the network for emergency services the conditions for AMF in clause 5.16.4.3 apply.