IVE state (see below) when not in active communication. In these states, a UE is just performing cell reselection to camp on the best cell, staying up to date with System Information Broadcast information, and monitoring Paging for downlink data and Public warning messages. 3.4 NR Protocol Stack RRC_CONNECTED Release with Suspend Resume Release Reject RRC_INACTIVE Setup Release RRC_IDLE Figure 3.4.9 RRC states and state transitions. NR introduces a new RRC state called INACTIVE, which is similar to the IDLE state in terms of the UE actions. A UE in this state keeps a copy of the previous RRC configuration, including the security configuration before it went into the INACTIVE state. The UE con- figuration, context, and the connection to the core network are also maintained in the gNB. These configurations are kept suspended. Figure 3.4.9 shows the transitions between different RRC states. The procedures to trigger state transitions are discussed in the following subsections. 3.4.5.2 RRC Procedures and Functions NR RRC defines a set of procedures that are functionally and procedurally similar to LTE. RRC connection control is a set of procedures that support the establishment and release of the RRC connection. It covers the procedures responsible for UE initial access to the network and the set up of security in the AS. 3.4.5.2.1 RRC Connection Establishment The RRC Connection establishment procedure is used to move the UE from RRC state IDLE to CONNECTED in order to communicate with the network. From the core network per- spective, this procedure may also involve registration with the 5GC to obtain 5G services. An example AS message flow for registration is shown in Figure 3.4.10. 1. A UE in IDLE that intends to perform a NAS registration procedure to attach to the network initiates a RACH procedure with a RACH preamble. 2. The gNB responds with a RAR message providing the timing advance and resources to use for the subsequent uplink message. These messages are defined in MAC specifica- tion (3GPP TS 38.321). 3. T