Section: 9.2.1.3 State Transitions
Content: The following figure describes the UE triggered transition from RRC_IDLE to RRC_CONNECTED (for the NAS part, see TS 23.502[ Procedures for the 5G System (5GS) ]  [22]): Figure 9.2.1.3-1: UE triggered transition from RRC_IDLE to RRC_CONNECTED 1. The UE requests to setup a new connection from RRC_IDLE. 2/2a. The gNB completes the RRC setup procedure. NOTE: The scenario where the gNB rejects the request is described below. 3. The first NAS message from the UE, piggybacked in RRCSetupComplete, is sent to AMF. 4/4a/5/5a. Additional NAS messages may be exchanged between UE and AMF, see TS 23.502[ Procedures for the 5G System (5GS) ]  [22]. 6. The AMF prepares the UE context data (including PDU session context, the Security Key, UE Radio Capability and UE Security Capabilities, etc.) and sends it to the gNB. 7/7a. The gNB activates the AS security with the UE. 8/8a. The gNB performs the reconfiguration to setup SRB2 and DRBs for UE, or SRB2 and optionally DRBs for IAB-MT. 9. The gNB informs the AMF that the setup procedure is completed. NOTE 1: RRC messages in step 1 and 2 use SRB0, all the subsequent messages use SRB1. Messages in steps 7/7a are integrity protected. From step 8 on, all the messages are integrity protected and ciphered. NOTE 2: For signalling only connection, step 8 is skipped since SRB2 and DRBs are not setup. The following figure describes the rejection from the network when the UE attempts to setup a connection from RRC_IDLE: Figure 9.2.1.3-2: Rejection of UE triggered transition from RRC_IDLE 1. UE attempts to setup a new connection from RRC_IDLE. 2. The gNB is not able to handle the procedure, for instance due to congestion. 3. The gNB sends RRCReject (with a wait time) to keep the UE in RRC_IDLE.