5.2.5 Access control and barring

When the UE needs to transmit an initial NAS message, the UE shall request to establish or resume an RRC Connection first and the NAS shall provide the RRC establishment or resume related information to the lower layer. The RAN handles the RRC Connection with priority during and after the RRC Connection Establishment procedure or RRC Connection Resume procedure, when UE indicates priority in Establishment or Resume related information

Under high network load conditions, the network may protect itself against overload by using the Unified Access Control functionality for 3GPP access specified in TS 22.261 [2], TS 24.501 [47] and TS 38.300 [27] to limit access attempts from UEs. Depending on network configuration, the network may determine whether certain access attempt should be allowed or blocked based on categorized criteria, as specified in TS 22.261 [2] and TS 24.501 [47]. The NG-RAN may broadcast barring control information associated with Access Categories and Access Identities as specified in TS 38.300 [27].

The NG-RAN node may initiate such Unified Access Control when:

• AMFs request to restrict the load for UEs that access the network by sending OVERLOAD START message containing conditions defined in clause 5.19.5.2, or
• requested by OAM, or
• triggered by NG-RAN itself.

If the NG-RAN node takes a decision to initiate UAC because of the reception of the N2 interface OVERLOAD START messages, the NG-RAN should only initiate such procedure if all the AMFs relevant to the request contained in the OVERLOAD START message and connected to this NG-RAN node request to restrict the load for UEs that access the network.

If the UE supports both N1 and S1 modes NAS and, as defined in TS 23.401 [26], the UE is configured for Extended Access Barring (EAB) but is not configured with a permission for overriding Extended Access Barring (EAB), when the UE wants to access the 5GS it shall perform Unified Access Control checks for Access Category 1 on receiving an indication from the upper layers as defined in TS 24.501 [47], TS 38.331 [28], TS 36.331 [51].

If the UE supports both N1 and S1 modes NAS and, as defined in TS 23.401 [26], the UE is configured with a permission for overriding Extended Access Barring (EAB), when the UE wants to access the 5GS it shall ignore Unified Access Control checks for Access Category 1 on receiving an indication from the upper layers, as defined in TS 24.501 [47].

NOTE: UE signalling of Low Access Priority indication over N1 in 5GS is not supported in this release of the specification.

Operator may provide one or more PLMN-specific Operator-defined access category definitions to the UE using NAS signalling and the UE handles the Operator-defined access category definitions stored for the Registered PLMN, as specified in TS 24.501 [47].

The access control for the Disaster Roaming is described in TS 23.122 [17] and TS 24.501 [47].