3GPP 23.501 v20.2.0 — the document's own text

5.9.3 Permanent Equipment Identifier

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).

A Permanent Equipment Identifier (PEI) is defined for the 3GPP UE accessing the 5G System.

The PEI can assume different formats for different UE types and use cases. The UE shall present the PEI to the network together with an indication of the PEI format being used.

If the UE supports at least one 3GPP access technology (i.e. NG-RAN, E-UTRAN, UTRAN or GERAN), the UE must be allocated a PEI in the IMEI or IMEISV format.

If a UE has registered with a network by using a network subscription and a PEI of the UE, then the UE shall keep the PEI to be used with the network subscription and shall not use that PEI with another network subscription while the UE is in registered state in the network.

In the scope of this release, the PEI may be one of the following:

for UEs that support at least one 3GPP access technology, an IMEI or IMEISV, as defined in TS 23.003 [19];
PEI used in the case of W-5GAN access as further specified in TS 23.316 [84].
for UEs not supporting any 3GPP access technologies, the IEEE Extended Unique Identifier EUI-64 [113] of the access technology the UE uses to connect to the 5GC.