ssage: REGISTRATION REQUEST to the gNB. The message contains the identifier of the mobile (SUPI/SUCI or 5G-TMSI), the previous TAI if it exists, the expected S-NSSAI slices, the capacity of the mobile and the list of PDU sessions if it exists: - the REGISTRATION REQUEST message is carried by the RRC SetupComplete request on the radio interface NR, and by the NGAP Initial UE Message on the NG-C interface; - the NGAP Initial UE Message contains user location information, such as the NCGI cell identifier (NR Cell Global Identifier) and the identity of the TAI location area of the mobile. 2) When the AMF function receives the REGISTRATION REQUEST message, it either contacts the UDM entity (if the mobile has transmitted its private SUCI or SUPI identifier) or the AMF function that the mobile was previously registered on (if the mobile has transmitted its 5G identifier ng-GUTI): - if the mobile was already registered on the network, it sends its 5G-GUTI identifier instead of the SUCI or SUPI. From 5G-GUTI, the gNB entity transmits the registration request to the AMF function that the mobile was previously NG-RAN and 5G-NR registered on. If this AMF function cannot be reached, the gNB entity chooses another AMF function. This new AMF function will contact the previous AMF function that the mobile was previously registered on. The goal is to be able to recover the SUCI or SUPI identifier. If the AMF function removed the context of the mobile, then the AMF is no longer able to provide the SUPI or SUCI identity. In this case, the AMF function requests that the mobile provides its private identity IMSI by using the NAS IdentityRequest request. This message is carried by the RRC DLInformation Transfer request on the radio interface NR, and by the NGAP DL NAS Transport message on the NG-C interface; - the mobile sends its private identity in the NAS IdentityResponse request carried by the RRC ULInformation Transfer request on the radio interface NR, and by the NGAP UL NAS Transport message on the NG-C interface. At the end of