Timer Expiry Handling Call Flow

This section describes the Timer Expiry Handling call flow.

Timer Expiry Handling Call Flow
Timer Expiry Handling Call Flow Description

Step

Description

1, 2, 3

The initial attach and Session Stale Timer updates are sent to CDL and the timer starts. The sequence is as follows:

  • Initial Attach Success

  • Session Stale Timer created

  • CDL updates done.

  • CDL starts Time (eval time) and waits for update session.

Note

Session Stale Timer is Reset or Restart, when any of the activity or transaction happens on the Control Plane (cnSGW-C).

4, 5

The Timer expires on CDL pod, and the timer sends notification to cnSGW-C. The sequence is as follows:

  • If no Session update received for eval timer duration

  • Timer Expiry on CDL pod

  • CDL sends Timer Notification to cnSGW-C

6–13

The session cleanup is activated, when the Session Stale Timer expires, and the timer reset isn’t required. The sequence is as follows:

  • Receives Timer Notification on cnSGW-C

  • If the Timer Notification is for Session Stale Timer and if the timer reset isn’t required, it starts UE session clean-up activities.

  • Sends Sx_Session_Modification_Req to UPF to set FAR Action=Drop, Sx_Session_Modification response received

  • Sends Delete Bearer Request towards MME

  • Sends Delete Session Request toward PGW

  • Sends Sx_Session_Delete_Request toward UPF to clean up User Plane data