EQUEST S-NSSAI list supported by TA NG SETUP RESPONSE S-NSSAI list supported by PLMN NG SETUP REQUEST S-NSSAI list supported by TA NG SETUP RESPONSE S-NSSAI list supported by PLMN Figure 3.11. The NG-C interface configuration procedure If the AMF function should be updated, to ensure interoperability on the NG-C interface, the AMF function informs the NG-RAN nodes of the corresponding S-NSSAI and TAI evolution (Figure 3.12). NG-RAN and 5G-NR RAN CONFIGURATION UPDATE RAN CONFIGURATION UPDATE ACKNOWLEDGE Figure 3.12. Procedure for updating the AMF function The mobile transmits its requested S-NSSAI slices to the gNB in the RRC ConnectionSetupComplete message. The gNB entity selects the AMF function from the NSSAI flag when different AMF are candidates. The gNB entity load balances the source AMF function from among all of the candidates. However, the selection made by the gNB entity is not necessarily optimal. The source AMF function which receives the attachment request first checks the S-NSSAI network slices authorized for the mobile, using the UDN database. From S-NSSAI, the AMF queries the NSSF network slice selection function (Network Slice Selection Function) and the NRF (Network Repository Function) discovery function in order to find out the target AMF function offered by the core network. If the target AMF function for registration is different from the source AMF function, a re-selecting procedure is triggered. The procedure for re-selecting the AMF function is described in Figure 3.13 for option A, and in Figure 3.14 for option B. In the case of option A, depending on the subscription and local policy information, the source AMF decides to send the initial request to the target AMF via the Namf_Communication_N1MessageNotify message carrying the NG-RAN Reroute Message. However, since there can only be one end point N2 between the gNB and the AMF for a given UE, the target AMF will update the end point to the gNB via the NG AMF Configuration message. In the case of option B, depending on the subscription a