Editing My 3GPP 33.501 notes (section)

=== 6.12.4 Subscription identification procedure ===
<span style="color:red">The subscriber identification mechanism may be invoked by the serving network when the UE cannot be identified by means of a temporary identity (5G-GUTI)</span>. In particular, <span style="color:red">it should be used when the serving network cannot retrieve the SUPI based on the 5G-GUTI by which the subscriber identifies itself on the radio path</span>.

The mechanism described in following figure allows the identification of a UE on the radio path by means of the SUCI.

[[File:Subscriber identifier query.png|center]]

The mechanism is initiated by the AMF that requests the UE to send its SUCI.

The UE shall calculate a fresh SUCI from SUPI using the Home Network Public Key, and respond with Identity Response carrying the SUCI. The UE shall implement a mechanism to limit the frequency at which the UE responds with a fresh SUCI to an Identity Request for a given 5G-GUTI.
:NOTE 1: If the UE is using any other scheme than the null-scheme, the SUCI does not reveal the SUPI.

AMF may initiate authentication with AUSF to receive SUPI as specified in clause 6.1.3.

In case the UE registers for Emergency Services and receives an Identity Request, the UE shall use the null-scheme for generating the SUCI in the Identity Response.
:NOTE 2: Registration for Emergency does not provide subscription identifier confidentiality.