3GPP 23.501 v20.2.0 — the document's own text
5.17.5.2.2 Interworking without N26 interface
Taught in 19. Living next to 4G (The 5G system architecture, in depth), 7. Roaming, other accesses, the edge and the outside (The 5G system architecture, overview).
In addition to the interworking principles documented in clause 5.17.2.3, the additional behaviour at EPS to 5GS mobility in clause 5.17.5.2.1 also applies.
When SCEF+NEF performs the procedure of monitoring via the AMF as described in clause 4.15.3.2.4 ("Exposure with bulk subscription") in TS 23.502 [3], if the AMF determines the interworking without N26 interface is supported, during mobility from 5GS to EPS, the AMF shall subscribe on behalf of SCEF+NEF for UDM+HSS notification of MME ID as described in clause 7.1.2 to trigger the SCEF+NEF to configure the monitoring request to the new MME. For single-registration mode, when UE's mobility from 5GS to EPS happens and Serving MME sends Update Location Request to the UDM+HSS, the UDM+HSS provides Serving MME ID to the SCEF+NEF which is the notification endpoint based on the subscription request from AMF. Then the SCEF+NEF performs the procedure of configuring monitoring via the MME for the same Monitoring Events as described in clause 5.6.2.1 of TS 23.682 [36].
When SCEF+NEF performs the procedure of monitoring via the UDM+HSS as described in clause 4.15.3.2.2 of TS 23.502 [3], when UE's mobility between 5GS and EPS happens, the UDM+HSS performs the procedure of configuring monitoring at the MME as described in clause 5.6.1.1 of TS 23.682 [36] and at the AMF as described in clause 4.15.3.2.1 of TS 23.502 [3].