Generating EPS PDN Connection Parameters from 5G PDU Session Parameters

This section describes how to generate the EPS PDN connection parameters from the 5G PDU session parameters in the PGW-C+SMF.

When the PGW-C+SMF is requested to set up or modify a PDN connection or a PDU session that supports interworking between EPS and 5GC, the PGW-C+SMF generates the PDN connection parameters from the PDU session parameters.

When the PGW-C+SMF generates the PDN connection parameters based on the PDU session parameters, the following rules hold:

  • PDN Type: The PDN type is set to IPv4 or IPv6 if the PDU Session Type is IPv4 or IPv6 respectively. The PDN type is set to Non-IP for Ethernet and Unstructured PDU Session Types.

  • EPS Bearer ID: The EBI is requested from the AMF during the establishment of a QoS Flow as described in 3GPP TS 23.502, section 4.11.1.4.1, for PDU sessions that support interworking between EPS and 5GC. The EBI is obtained from MME during the establishment of an EPS bearer (that is triggered by an establishment of the QoS Flow) as defined in 3GPP TS 23.401 for PDN connections hosted by PGW-C+SMF. The association between EBI and QoS Flow is stored by the SMF.

  • APN-AMBR: APN-AMBR is set according to the operator policy. For example, taking the session AMBR into account.

  • EPS QoS parameters (including ARP, QCI, GBR, and MBR):

    • If the QoS Flow is mapped to one EPS bearer: ARP, GBR, and MBR of the EPS bearer is set to the respective ARP, GFBR, and MFBR of the corresponding QoS Flow.

    • For standardized 5QIs, the QCI is mapped 1:1 to the 5QI. For non-standardized 5QIs, the PGW-C+SMF derives the QCI based on the 5QI and operator policy.

Note

A GBR QoS flow is mapped 1:1 to a GBR dedicated EPS Bearer if an EBI has been assigned. All other GBR QoS flows will be terminated during interworking. If multiple QoS flows are mapped to one EPS bearer, the EPS bearer parameters are set based on the operator policy. For example, EPS bearer QoS parameters are set according to the highest QoS of all mapped QoS flows.

Note

Non-GBR QoS flows for which no EBI has been assigned are mapped to the default EPS bearer.