Feature Description

Important

The PGW-C term used in this chapter denote the EPS interworking functionality supported by SMF and must not be assumed as a standalone P-GW that is used in the LTE network.

For UEs, the SMF supports both 5G and 4G NAS to connect to E-UTRAN and 5G core network. The SMF includes the EPS interworking support and acts as PGW-C+SMF. The SMF uses the S5/S8 interface to receive the 4G Session Creation Request. Gx, Gy, or Gz interfaces, used for 4G session creation are replaced with the corresponding 5G core SBI interfaces, such as the NPCF and NCHF.

After a PDU session creation on PGW-C+SMF through E-UTRAN, MME, and S-GW, the SMF performs the 4G to 5G data session handover.

Alternate RAT Tunnel Creation for 5G

SMF creates an alternate RAT tunnel during 5G sessions for the 5G PDU establishment scenarios. This tunnel is reused when a subscriber moves to another RAT during handover.

Note

Creation of an alternate RAT tunnel is a prerequisite for the inter-PLMN handover support.