ation of the UE context to the AMF function with the NGAP Initial Context Setup Response message. This step follows the successful securing of the radio link. RRC SetupRequestComplete (NAS Registration Request, Registration Type, 5G Id, Last TAI NGAP Initial UE Message Requested S-NSSAI, UE Capability, List of PDU Sessions) Optional: NGAP DL NAS TRANSPORT Optional: RRC DL Information Transfer NAS Identity Request NAS Identity Request Optional: RRC UL Information Transfer Optional: NGAP UL NAS TRANSPORT NAS - Identity Response SUCI NAS Identity Response NGAP DL NAS TRANSPORT RRC DL Information Transfer NAS - Authentication Request (RAND, AUTN, ngKSI, ABBA) NAS - Authentication Request (RAND, AUTN, ngKSI, ABBA) RRC UL Information Transfer NGAP UL NAS TRANSPORT NAS - Authentication Response (RES) NAS - Authentication Response (RES) NGAP DL NAS TRANSPORT RRC DL Information Transfer NAS - Security Mode Command NAS Security Mode Command RRC UL Information Transfer NAS - Security Mode Complete NGAP UL NAS TRANSPORT NAS - Security Mode Complete Figure 3.9. Registration procedure: authentication and the NAS secure mode. For a color version of this figure, see www.iste.co.uk/launay/5g.zip NG-RAN Network - Procedures NGAP Initial Context Setup Request RRC : SecurityModeCommand UE Context RRC : SecurityModeComplete RRC : Reconfiguration (NAS Registration Request, Meas Config, SCell) RRC : ReconfigurationComplete NGAP Initial Context Setup Response Figure 3.10. Registration procedure - service access and registration. For a color version of this figure, see www.iste.co.uk/launay/5g.zip 3.2.3.4. The AMF function reallocation procedure The NG interface management procedure allows NG-C interoperability information to be exchanged between the NG-RAN node and the core network. The network node interrogates the AMF function via the NG SETUP REQUEST, in order to find out the S-NSSAI network slices supported by the AMF function on a TA (tracking area). The AMF informs the NG-RAN node in the NG SETUP RESPONSE (Figure 3.11). NG SETUP R