User Plane Connection Reactivation Request

The following call flows captures information on UE idle mode mobility from EPS to 5GS with UP (User Plane) connection reactivation using N26 interface.

User Plane Connection Reactivation Request
User Plane Connection Reactivation Request

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.

  • the PDU Sessions Activate List attribute, including the PDU Session ID of all the PDU session(s) to be re-activated.

  • 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 Context 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.

and, if the PDU session that is derived by the SMF based on the EPS bearer contexts was requested to be re-activated, i.e. if the PDU Session ID was present in the PDU Sessions Activate List,

  • the User Plane Connection State attribute is set to ACTIVATING.

  • N2 SM information to request the 5G-AN to assign resources to the PDU session (PDU Session Resource Setup Request Transfer), including the transport layer address and tunnel endpoint of the uplink termination point for the user plane data for this PDU session (i.e. UPF's GTP-U F-TEID for uplink traffic).

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.

3

If the SMF returns a 200 OK response, the AMF subsequently updates the SM context in the SMF by sending POST request with the following information:

  • N2 SM information received from the 5G-AN (PDU Session Resource Setup Response Transfer IE), including the transport layer address and tunnel endpoint of one or two downlink termination point(s). It also includes the associated list of QoS flows for this PDU session (i.e. 5G-AN's GTP-U F-TEID(s) for downlink traffic), if the 5G-AN succeeded in establishing resources for the PDU sessions; or

  • N2 SM information received from the 5G-AN (PDU Session Resource Setup Unsuccessful Transfer IE), including the Cause of the failure, if resources failed to be established for the PDU session.

Upon receipt of this request, the SMF:

  • Updates the UPF with the 5G-AN's F-TEID(s) and sets the User Plane Connection State attribute to ACTIVATED, if the 5G-AN succeeds in establishing resources for the PDU sessions; or

  • Considers that the activation of the User Plane connection has failed and sets the User Plane Connection State attribute to DEACTIVATED.

4

SMF returns a 200 OK response including the User Plane Connection State attribute representing the final state of the user plane connection.