Section: 4.11.2 Interworking procedures without N26 interface 4.11.2.1 General
Content: Clause 4.11.2 defines the procedures to support interworking between 5GS and EPS without any N26 interface between AMF and MME. During interworking from EPS to 5GS, as the SMF+PGW-C may have different IP addresses when being accessed over S5/S8 and N11/N16 respectively, the AMF shall discover the SMF instance by an NF/NF service discovery procedure using the FQDN for the S5/S8 interface received from the UDM as a query parameter. This is required for both non-roaming and roaming with local breakout, as well as for home routed roaming. NOTE: As the AMF is not aware of the S-NSSAI assigned for the PDN Connection, the NF/NF service discovery used to find the SMF instance can use PLMN level NRF.