procedure is successful, the AMF replies with NG Setup Response, carrying the list of Globally Unique AMF IDs (GUAMIs), the list of PLMNs supported by the AMF, and some additional information. If some of the information conveyed during the NG Setup pro- cedure changes in either gNB or AMF, each node can notify the other about such changes using RAN Configuration Update and AMF Configuration Update procedures, respectively. Those procedures can also be used to add or remove additional SCTP associations. If an AMF experiences overload, it can request the NG-RAN to reduce signaling traffic UEs may generate toward it. This is performed using the Overload Start procedure, which also carries the information about which traffic an AMF is requesting to reject. For example, an AMF may request to reject all RRC connection requests or allow only emergency ser- vices. The Overload Stop procedure is used to indicate that the AMF can now accept all signaling traffic. Interface management messages use non-UE-associated signaling. 3.3.3.1.2 NAS Transport and UE Context Management When a UE connects to the network, for example, during the registration procedure, a gNB selects an AMF for the UE and establishes a UE association between the two network nodes. This is performed using the Initial UE Message (which is part of the NAS transport NG-AP messages category) and Initial UE Context Setup Request/Response (which are part of the UE context management NG-AP messages category). NAS transport messages are: Initial UE message Downlink/Uplink NAS transport Others (NAS Non-Delivery Indication, Reroute NAS request). UE context management messages are: Initial Context Setup Request/Response/Failure messages UE Context Release Request/Command/Complete messages UE Context Modification Request/Response/Failure messages RRC Inactive transition report message. 3 5G System Overview UE in RRC_IDLE CM-IDLE 1. RRC connection establishment UE in RRC_CONNECTED CM-IDLE 2. INITIAL UE MESSAGE UE in RRC_CONNECTED CM-CONNECTED 3. DOWNLINK NAS TRANSPORT