 4. DLInformation Transfer 5. ULInformation Transfer 6. UPLINK NAS TRANSPORT 7. INITIAL CONTEXT SETUP REQUEST 8. AS security activation, DRBs setup 9. INITIAL CONTEXT SETUP RESPONSE Figure 3.3.4 IDLE to CONNECTED state transition. (Source: Reproduced by permission of © 3GPP). Downlink and Uplink NAS transport procedures are rather self-explanatory - they are used to transfer NAS PDUs to/from a UE, respectively. Additionally, certain information can be piggybacked to them. For example, in the uplink, the NAS transport procedure can carry the UE location information. In the downlink, the message can also carry the mobility restric- tion list, UE aggregate maximum bit rate, and others, in case this information needs to be updated. The usage of some of these procedures can be illustrated by the UE-triggered service request, which is the procedure performed when an idle mode UE has signaling or uplink data to send. The procedure is shown in Figure 3.3.4 in a simplified form, where interactions inside the 5GC are hidden. As a result of this procedure, a UE transitions from RRC_IDLE to RRC_CONNECTED RAN state (and from CM-IDLE to CM-CONNECTED 5GC state), establishes the signaling connection with an AMF, and may send messages. 0. A UE is in RRC_IDLE (from NG-RAN perspective) and in CM-IDLE (from 5GC perspective). 1. If the UE decides to send uplink data, it establishes an RRC connection. When an RRC connection is established, the UE moves from RRC_IDLE to RRC_CONNECTED. 2. In order to notify the core network and to allow e.g. establishment of PDU sessions for the UE, the gNB sends NG-AP Initial UE Message to the AMF, which carries the Service 3.3 NG Radio Access Network Request NAS message received from the UE and other information, such as selected PLMN ID, user location information, etc./4./5./6. Additional NAS messages may be exchanged between UE and AMF (not shown for brevity). 7. The AMF prepares the UE context data and sends it to the gNB in the Initial Context Setup Request. The Initial Context Setup Request typic