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

5.34.8 Support for Cellular IoT

Taught in 26. Relays, satellites, femtos and shared networks (The 5G system architecture, in depth).

This clause defines the specific impacts of deployments topologies with specific SMF Service Areas on how 5GS supports Cellular IoT as defined in clause 5.31.

For a PDU Session supporting Control Plane CIoT 5GS Optimisation as defined in clause 5.31.4:

For a PDU Session towards a DNN/S-NSSAI for which the SMF Selection Subscription data includes an Invoke NEF Indication (i.e. for a PDU Session which will be anchored in NEF), the AMF never inserts an I-SMF.

When an I-SMF is inserted to serve a PDU Session, the I-SMF supports the features that, as specified in clause 5.31, apply to the V-SMF in the case of Home Routed.

NOTE: This can require the SMF to subscribe onto I-SMF about RAT type change for a PDU Session as described in clause 4.23 of TS 23.502 [3].