UE-requested PDU Session Modification Call Flow

This section describes the UE-requested PDU session modification procedure in which the Always-on PDU session indication is sent.

The following figure illustrates the UE-requested PDU Session Modification call flow.

UE-requested PDU Session Modification Call Flow


UE-requested PDU Session Modification Call Flow Description
Step Description
1

The UE sends an "Always-on PDU Session Requested" IE in the PDU Session Modification Request message.
2

The SMF checks the DNN profile to determine whether the always-on support is enabled.
3

The SMF includes "Always-on PDU Session Indication" in the PDU Session Modification Command when one of the following is true:

  • "Always-on PDU Session Indication" is sent with the value as "enabled" when the always-on configuration is enabled under the DNN profile.

  • "Always-on PDU Session Indication" is sent with the value as "disabled" when the "Always-on PDU Session Request" IE is received and configuration is disabled.
4

The SMF does not include the "Always-on PDU Session Indication" only when both these conditions are true:

  • If the UE did not send the "Always-on PDU Session Requested" IE.

  • If the always-on configuration is disabled in the DNN profile.

Note

As per 3GPP TS 23502, for a PDU session that was established in the EPS, when the UE moves from EPS to 5GS for the first time, the UE includes an "Always-on PDU Session Requested" indication in the PDU Session Modification Request message if it wants to change the PDU session to an "always-on" PDU session.