4.8.4A.1 Core network selection

A UE that supports CIoT optimizations performs core network selection (i.e. it selects EPC or 5GCN) if the lower layers have provided an indication that the current E-UTRA cell is connected to both EPC and 5GCN as specified in 3GPP TS 23.501 [8].

When selecting a PLMN as described in 3GPP TS 23.122 [5], the UE shall select a core network type (EPC or 5GCN) based on:

• indication from the lower layers about the CIoT EPS optimizations supported in EPC;
• indication from the lower layers about the CIoT 5GS optimizations supported in 5GCN;
• the CIoT EPS optimizations supported by the UE;
• the CIoT 5GS optimizations supported by the UE;
• the UE's preferred CIoT network behaviour for EPC; and
• the UE's preferred CIoT network behaviour for 5GCN.

The UE shall provide the selected core network type information to the lower layer during the initial registration procedure.