PDU Session is in Inactive State

The following call flows captures information on UE Idle Mode Mobility from EPS to 5GS using N26 Interface when PDU session is in inactive state.

PDU Session in Inactive State
PDU Session in Inactive State

Step

Description

1

AMF sends a POST request towards SMF/PGW-C of each UE EPS PDN connection with following information:

  • UE EPS PDN connection, including the EPS bearer contexts, received from the MME, representing the individual SM context to be created.

  • EPS Bearer Context Status attribute, indicating the status of all the EPS bearer contexts in the UE, if corresponding information is received in the Registration Request from the UE.

2

Upon receipt of such a request, if:

  • a corresponding PDU session is found based on the EPS bearer contexts.

  • the default EPS bearer context of the corresponding PDU session is not reported as inactive by the UE in the EPS Bearer Connection Status attribute, if received; and

  • it is possible to proceed with moving the PDN connection to 5GS.

2a

SMF returns a 201 Created response including the following information:

  • PDU Session ID corresponding to the default EPS bearer ID of the EPS PDN connection.

  • Allocated EBI List, containing the EBI(s) allocated to the PDU session.

The Location header present in the POST response contains the URI of the created SM context resource.

AMF stores the association of the PDU Session ID and the SMF ID, and allocated EBI(s) associated to the PDU Session ID.

If the EPS Bearer Context Status attribute is received in the request, the SMF checks whether some EPS bearer(s) of the corresponding PDU session have been deleted by the UE but not notified to the EPS. If so, SMF releases these EPS bearers, corresponding QoS rules and QoS flow level parameters locally.

2b

SMF returns 4xx/5xx failure response if:

  • SMF determines that seamless session continuity from EPS to 5GS is not supported for the PDU session. SMF sets the cause attribute in the Problem Details structure to NO_EPS_5GS_CONTINUITY.

  • The default EPS Bearer Context of the PDU session is reported as inactive by the UE in the EPS Bearer Context Status attribute. SMF sets the cause attribute in the Problem Details structure to DEFAULT_EPS_BEARER_INACTIVE.