4G Session Support with 5GS SBI Interfaces
SMF leverages the 3GPP provision for the UEs that can support both 5G and 4G NAS to connect to both 4G and 5G core networks. With this provision, the SMF includes the EPS interworking support and acts as a PGW-C+SMF. The interfaces, such as the Gx, Gy, or Gz, which are used for a 4G session creation are replaced with the corresponding 5G core SBI interfaces, such as the Npcf and Nchf.
The following feature is related to this use case: