Section: 5.2.5 Access control and barring
Content: When the UE needs to transmit an initial NAS message, the UE shall request to establish an RRC Connection first and the NAS shall provide the RRC establishment related information to the lower layer. The RAN handles the RRC Connection with priority during and after RRC Connection Establishment procedure, when UE indicates priority in Establishment 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[ Service requirements for the 5G system ]  [2], TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47] and TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [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[ Service requirements for the 5G system ]  [2] and TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47]. The NG-RAN may broadcast barring control information associated with Access Categories and Access Identities as specified in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [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[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [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[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47], TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [28], TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [51]. If the UE supports both N1 and S1 modes NAS and, as defined in TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [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[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [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[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47]. The access control for the Disaster Roaming is described in TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [17] and TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47].