Stale Session Handling and Clearing

Feature Summary and Revision History

Summary Data

Table 1. Summary Data

Applicable Product or Functional Area

cnSGW-C

Applicable Platform

SMI

Feature Default Setting

Disabled - Configuration required to enable

Related Documentation

Not Applicable

Revision History

Table 2. Revision History

Revision Details

Release

First introduced

2021.02.3

Feature Description

The cnSGW-C supports identifying and clearing stale sessions using a session-stale-timer parameter in the SGW Profile configuration. An example of a stale session is one that is inactive and not read or modified for a specific period of time.

How it Works

This section describes how this feature works.

Call Flows

This section describes the key call flows for this feature.

Timer Expiry Handling Call Flow

This section describes the Timer Expiry Handling call flow.

Figure 1. Timer Expiry Handling Call Flow
Table 3. 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

Feature Configuration

To configure this feature, use the following configuration:

config 
   profile sgw sgw_profile_name 
   session-stale-timer session_stale_timer 
   end

NOTES:

  • session-stale-timer session_stale_timer —Specify the maximum number of seconds for which a session can remain idle without any signaling or event, after which the session will be terminated.

    The session_stale_timer value must be in the range of 0–4294967295, and must be greater than the setup-timeout and session-idle-timeout timer values.

    To disable the session-stale-timer configuration, set it to 0.

Configuration Example

The following is an example configuration.

config
   profile sgw sgw1
   session-stale-timer 120
   end

Configuration Verification

To verify the configuration:

show running-config profile sgw sgw1
session-stale-timer 120

The output of the show command includes the following field:

session-stale-timer—Indicates the maximum number of seconds for which a session can remain idle without any signaling or event, after which the session is terminated.

OAM Support

This section describes operations, administration, and maintenance information for this feature.

Bulk Statistics

The following statistics are supported for this feature

sgw_service_stats{app_name="smf",cluster="Local",data_center="DC",
fail_reason="",gr_instance_id="1",instance_id="0",interface="interface_sgw_egress",reject_cause="",
service_name="sgw-service",sgw_procedure_type="stale_session_initiated_deletion",status="attempted",
sub_fail_reason=""} 1
sgw_service_stats{app_name="smf",cluster="Local",data_center="DC",fail_reason="",
gr_instance_id="1",instance_id="0",interface="interface_sgw_egress",reject_cause="",
service_name="sgw-service",sgw_procedure_type="stale_session_initiated_deletion",status="success",
sub_fail_reason=""} 1
sgw_service_stats{app_name="smf",cluster="Local",data_center="DC",fail_reason="",
gr_instance_id="1",instance_id="0",interface="interface_sgw_ingress",reject_cause="",
service_name="sgw-service",sgw_procedure_type="stale_session_initiated_deletion",status="attempted",
sub_fail_reason=""} 1
sgw_service_stats{app_name="smf",cluster="Local",data_center="DC",fail_reason="",
gr_instance_id="1",instance_id="0",interface="interface_sgw_ingress",reject_cause="",
service_name="sgw-service",sgw_procedure_type="stale_session_initiated_deletion",status="success",
sub_fail_reason=""} 1
sgw_ue_disconnect_stats{app_name="smf",cluster="Local",data_center="DC",
gr_instance_id="1",instance_id="0",reason="stale_session_init_disconnect",
service_name="sgw-service"} 1
sgw_pdn_disconnect_stats{app_name="smf",cluster="Local",data_center="DC",
gr_instance_id="1",instance_id="0",pdn_type="ipv4",rat_type="EUTRAN",
reason="stale_session_init_disconnect",service_name="sgw-service"} 1