PEI — Permanent Equipment Identifier — the identity of the hardware, not the subscription

5G Systems Notes · Concept map · PEI Route · Hierarchy · Index · All concepts · Hub

The device — identity, state, mobility

Where it sits

Sits atLevel 4 of the hierarchy · The device — identity, state, mobility · explained
The 2 of them
IMEI — the equipment identity every 3GPP device must carry
IMEISV — the same, plus a software version
Learn firstSUPI — 4 concepts in the full chain, see the paths
UnlocksNothing else depends on it directly.
Primary clauseTS 23.501 §5.9.3
Used inref-ue-identity 10
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

What it is. The Permanent Equipment Identifier — the identity of the hardware, as distinct from the subscription. TS 23.501 §5.9.3. Where the SUPI says which subscription, the PEI says which box.

What form it takes, per the clause:

"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." · for devices supporting no 3GPP access technology, an IEEE EUI-64 · a separate form for wireline access.

The device "shall present the PEI to the network together with an indication of the PEI format being used."

Why the network wants it at all. Three reasons, and only the first is the famous one:

Blocking stolen equipment. A device reported stolen can be barred by IMEI even with a different subscription in it — the check is against an equipment identity register, reached over N17. Changing the SIM does not help, which is the entire point.

Knowing what the device is. An IMEI identifies a model, and a network that knows the model knows its quirks — including which capabilities to trust and which known firmware bugs to work around.

Regulatory identification, where an emergency or lawful-intercept context requires identifying the equipment rather than the subscriber.

One binding rule that is easy to miss. §5.9.3: "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."

That is a constraint written for multi-SIM devices. A phone with two active subscriptions must not present the same equipment identity on both while registered — otherwise one physical device would appear as one equipment serving two subscriptions simultaneously, and the equipment-based checks above would become ambiguous. Multi-SIM handsets carry more than one IMEI for exactly this reason, and this clause is why.

Read on

This concept is read as part of one argument in ref-ue-identity, alongside the rest of its group.

Widget not found: sim_status

Before this concept, the hierarchy says to learn the following — the full chain, in order:

To understand PEI (level 4) you first need 4 other concepts. Read them in this order — everything on one line can be read in any order, but no line before the one above it:
Level Learn these
0 5G Core
1 Network function
2 UDM
3 SUPI
Immediately before PEI: SUPI.
Keep going — where this sits on the route
◀5G-GUTIstep 43 · level 4
Step 44 of 118level 4 · The device
Point Astep 45 · level 5▶
Nothing depends on this one directly
It is a leaf of the graph — follow the route rather than the branch.
↳ all 14 concepts at level 5 · level 4 in full · the whole route
The route is every concept in the folder ordered by level, so nothing here needs anything after it. Computed at page load from terms.json; the same numbering as the route page.
5G Systems Notes · Concept map · PEI Top · Concept map · Hub