Call Flow

This section describes the call flow for the user plane activation of a PDU session.

The following figure illustrates the UE-initiated user plane activation call flow.

User Plane Connection Activation Call Flow
UE-initiated Idle to Active Transition Call Flow Description
Step Description
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 with the following information to request the 5G-AN to assign resources to the PDU session.

    • Transport layer address (IPv4 or IPv6 address of the UPF)

    • Tunnel endpoint of the uplink termination point for the UP data of current PDU session (that is, GTP-U F-TEID of UPF for uplink traffic)

3

Then, the AMF requests the SMF by sending POST request with the N2 SM information. If the 5G-AN succeeded in establishing resources for the PDU sessions, the N2 SM information includes the following information:

  • Transport layer address

  • Tunnel endpoint of the downlink termination point for the user data of the current PDU session. That is, GTP-U F-TEID of 5G-AN for downlink traffic.

4

The SMF initiates PFCP Session Modification procedure towards UPF with downlink FAR updated with the following options:

  • Forwarding Action enabled along with remote node forwarding parameter details, such as the IPv4 or IPv6 address of RAN and GTP-U F-TEID.

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