UE Authentication and Mobility Management AMF Interface Usage in 5G

The AMF unit plays a crucial role in the 5G core network; it is responsible for processing NAS messages transmitted transparently through the RAN (gNB) from the terminal (UE). The registration and authentication and mobility management of the terminal (UE) during initial access are completed by the AMF independently or jointly with other relevant network elements, as follows:

I. The order of AMF interface and message usage for 5G terminal authentication is shown in Figure (1);

Figure 1. Message usage order of UE authentication AMF interface in 5G.

• [11] UE authentication request
• [11] UE response
• [17] NRF discovery AUSF
• [25] Initialize SCP NF instance
• [11] NAMF Nausf authentication request
• [11] 5gAKA
• [11] Av5gAka contains authentication vector 5gAKA method
• [11] Amf_ue->SUCI
• [11] 5g AKA confirmation URL
• [11] SEAF starts authentication process
• [11] SUPI and Kseaf
• [11] Authentication successful
• [11] (or) Authentication failed

II. Mobility Management 5G networks provide high-speed and reliable connectivity for mobile users and devices, including vehicles, smartphones, and IoT devices. During mobility, the AMF is responsible for the transmission and processing of terminal-related information. Its interface (protocol) is used as follows;

Figure 2. Order of AMF interface messages used when the UE moves in 5G

• [5] Process registration request
• [5] UE sends initial NAS message to AMF
• [5] Set 5GS registration type: KSI, TSC
• [5] AMF new GUTI
• [5] Copy stream number, NR-TAI, NR-CGI from ran_ue
• [5] Check TAI[5] The algorithm selected by AMF should be the same as the NAS security algorithm
• [5] 5GMM request accepted
• [5] 5GMM processes registration update
• [5] 5GMM processes service request
• [6] The initial NAS service request message should contain security header type, ngKSI, TMSI and security header type
• [6] 5GMM processes service update[17] NRF discovers AUSF
• [25] Initialize SCP NF instance
• [5][6] AMF NAUSF authentication response, then confirm
• [5] Identity response SUCI[6] 5GMM status registered
• [13] NGAP handles path switching request
• [13] NGAP handles switching request
• [13] NGAP handles switching notification
• [13] NGAP handles Ran configuration update
• [5][6] 5GMM handles UL NAS transmission
• [5] 5GMM handles deregistration request
• [5] Set 5GS deregistration type
• [5] AMF sbi release all sessions
• [5] Clear paging information
• [5] Clear SM context
• [5] Unassociate NG with NAS