3GPP 23.501 v20.2.0 — the document's own text
5.9.1 General
Taught in 7. Every name the system uses (The 5G system architecture, in depth), 4. Knowing who you are and where you are (The 5G system architecture, overview).
Each subscriber in the 5G System shall be allocated one 5G Subscription Permanent Identifier (SUPI) for use within the 3GPP system. The 5G System supports identification of subscriptions independently of identification of the user equipment. Each UE accessing the 5G System shall be assigned a Permanent Equipment Identifier (PEI).
The 5G System supports allocation of a temporary identifier (5G-GUTI) in order to support user confidentiality protection.