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5GS – General Registration – 05 of 24
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).
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 IE, which may be integrity protected, to request the UE's SUPI and MM Context. See clause 5.2.2.2.2 for details of this service operation. The old AMF uses the integrity protected complete Registration request IE to verify 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 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.