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5GS-R1. General Registration
10 of 27 
Signalling flow for TS 23.502 General Register - Authentication/Security

Step 9a, verbatim
If authentication is required, the AMF requests it from the AUSF; if Tracing Requirements about the UE are available at the AMF, the AMF provides Tracing Requirements in its request to AUSF. Upon request from the AMF, the AUSF shall execute authentication of the UE. The authentication is performed as described in TS 33.501 [15]. The AUSF selects a UDM as described in TS 23.501 [2], clause 6.3.8 and gets the authentication data from UDM.
Once the UE has been authenticated the AUSF provides relevant security related information to the AMF. In case the AMF provided a SUCI to AUSF, the AUSF shall return the SUPI to AMF only after the authentication is successful.
After successful authentication in new AMF, which is triggered by the integrity check failure in old AMF at step 5, the new AMF invokes step 4 above again and indicates that the UE is validated (i.e. through the reason parameter as specified in clause
Step 9b, verbatim
If NAS security context does not exist, the NAS security initiation is performed as described in TS 33.501 [15]. If the UE had no NAS security context in step 1, the UE includes the full Registration Request message as defined in TS 24.501 [25].
The AMF decides if the Registration Request needs to be rerouted as described in clause, where the initial AMF refers to the AMF.
Step 9c, verbatim
The AMF initiates NGAP procedure to provide the 5G-AN with security context as specified in TS 38.413 [10] if the 5G-AN had requested for UE Context. In addition, if Tracing Requirements about the UE are available at the AMF, the AMF provides the 5G-AN with Tracing Requirements in the NGAP procedure.
Step 9d, verbatim
The 5G-AN stores the security context and acknowledges to the AMF. The 5G-AN uses the security context to protect the messages exchanged with the UE as described in TS 33.501 [15].