UE-initiated Idle to Active Transition

The following call flow depicts the UE-initiated idle to active transition.

Idle to Active Transition (UE-Initiated) Call Flow
Idle to Active Transition (UE-Initiated) Call Flow Description
StepDescription
1

The AMF requests SMF to activate the user plane connection of the PDU session by sending a POST request with the following information:

  • upCnxState attribute set to ACTIVATING.

  • User location, user location timestamp and access type associated to the PDU session (if modified).

  • Other information (if necessary).

2

Upon receipt of the request, the SMF starts activating the N3 tunnel of the PDU session. The SMF returns a 200 OK response with the following information:

  • upCnxState attribute set to ACTIVATING;

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

3

Subsequently, the AMF requests the SMF by sending POST request with the following information:

  • N2 SM information received from the 5G-AN, including the transport layer address and tunnel endpoint of the downlink termination point for the user data for the current PDU session (i.e. 5G-AN's GTP-U F-TEID for downlink traffic), if the 5G-AN succeeded in establishing resources for the PDU sessions.

4

The SMF initiates PFCP Session Modification Procedure towards UPF with down link FAR updated with the following options:

  • Forwarding Action enabled along with remote node “forwarding parameters” details like the IP address and GTP-U F-TEID.

5Upon receipt of successful response from UPF node, the SMF sets the upCnxState attribute to ACTIVATED for the PDU session.
6SMF then initiates 200 OK response including the upCnxState attribute set to ACTIVATED towards AMF.