Understanding TS 133 501 (5G) Step 2 of EAP-AKA’

I got a question dealing with the EAP-AKA’ used in 5G to authenticate clients coming from a 3GPP-Network.

I read the latest specification on ETSI. The problem which I have is based on Step 2 on Page 37/38, where it says (at least I understood it like that), that when the UDM/ARPF got the SUCI it shall continue as shown in RFC 5448 (a description of a EAP-AKA’), otherwise it shall follows the EAP-AKA’ shown in the specification (TS 133 501).

That’s what confuses me. Are there really two different implementations of the EAP-AKA’? I tried to layer those two, but ntl for me those two are different, due to the message flow.
Is that correct?

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Author: Sheena