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5GS – General Registration – 05 of 25
Signalling flow for TS 23.502 General Register - new AMF to old AMF: Namf_Communication_UEContextTransfer


Step 4, verbatim
[Conditional] new AMF to old AMF: Namf_Communication_UEContextTransfer (complete Registration Request) or new AMF to UDSF: Nudsf_Unstructured Data Management_Query().
(With UDSF Deployment): If the UE's 5G‑GUTI was included in the Registration Reqest and the serving AMF has changed since last Registration procedure, new AMF and old AMF are in the same AMF Set and UDSF is deployed, the new AMF retrieves the stored UE's SUPI and UE context directly from the UDSF using Nudsf_UnstructuredDataManagement_Query service operation or they can share stored UE context via implementation specific means if UDSF is not deployed. This includes also event subscription information by each NF consumer for the given UE. In this case, the new AMF uses integrity protected complete Registration request NAS message to perform and verify integrity protection.
(Without UDSF Deployment): If the UE's 5G‑GUTI was included in the Registration Request and the serving AMF has changed since last Registration procedure, the new AMF may invoke the Namf_Communication_UEContextTransfer service operation on the old AMF including the complete Registration Request NAS message, which may be integrity protected, to request the UE's SUPI and UE Context. See clause 5.2.2.2.2 for details of this service operation. In this case, the old AMF uses either 5G‑GUTI and the integrity protected complete Registration request NAS message, or the SUPI and an indication that the UE is validated from the new AMF, to verify integrity protection if the context transfer service operation invocation corresponds to the UE requested. The old AMF also transfers the event subscriptions information by each NF consumer, for the UE, to the new AMF.
NOTE 1: The new AMF sets the indication that the UE is validated according to step 9a, in case the new AMF has performed successful UE authentication after previous integrity check failure in the old AMF.
NOTE 2: The NF consumers does not need to subscribe for the events once again with the new AMF after the UE is successfully registered with the new AMF.
If the new AMF has already received UE contexts from the old AMF during handover procedure, then step 4, 5 and 10 shall be skipped.
For an Emergency Registration, if the UE identifies itself with a 5G‑GUTI that is not known to the AMF, steps 4 and 5 are skipped and the AMF immediately requests the SUPI from the UE. If the UE identifies itself with PEI, the SUPI request shall be skipped. Allowing Emergency Registration without a user identity is dependent on local regulations.