Feature Description

During the UE session establishment in 5G core network, the SMF uses the existing UPF selection logic and records the index of the selected UPF in PGW-C Control Tunnel Endpoint Identifier (TEID).

Upon receiving Create Session Request (CSR) from MME, cnSGWc checks whether or not the TEID value is zero. If it is zero, then cnSGWc sends Remote Procedure Call (gRPC) message to SMF and fetches UP ID and UPF IP.

If the TEID is non-zero, the SMF checks the bits from 21 through 30 of control TEID value, and extracts the UPF index. The SMF uses the extracted UPF index to select the preferred UPF.

The SGW-C uses this as the preferred UPF when the UE session is handed over to EPS network. If the preferred UPF is present in the list returned by the UPF selection algorithm, then the cnSGWc selects the UPF with highest priority. That is, the cnSGWc selects the same UPF that was chosen by SMF. This operation enables creating an optimized data path for the UE.

If the preferred UPF does not exist in the returned list, cnSGWc selects a different UPF.