This chapter describes the
implementation of a timer to track inactive sessions and to cleanup the
sessions once the timer expires.
Idle timeout is
used to track the inactive sessions on ePDG and clean them up once they have
been idle for certain duration as defined by the idle timeout value. Currently,
AAA provides PDN Inactivity timer value per session to ePDG via SWm interface.
Both active and standby chassis track idle time of inactive sessions so that
they can be removed from the chassis post timeout. The active chassis tracks
the active sessions and notifies the standby chassis at every periodic timer
expiry that the session is not idle. On the active chassis, both the Session
Manager and ICSR framework track the active sessions and notify the standby
periodically that the session is not idle.
send idle micro checkpoints every 10 seconds to corresponding session manager
on the standby chassis.
To avoid frequent
periodic idlesec micro checkpoints, Interval at which these checkpoints are
sent is made configurable.
Also an event
driven mechanism for idlesec micro checkpoints for ePDG is allowed to eliminate
the overhead associated with periodic idlesec micro checkpoints.
on Periodic Idle Seconds Micro-checkpoints
In this approach the existing hard
coded idle timer of Session Manager is configurable per APN.
This approach involves:
A new CLI is provided to
configure the periodic idle second micro checkpointing timer.
Timer is configurable on per APN basis. The default timer value
is 10 Seconds.
Value "0" means disabled i.e. the change from micro checkpointing
to standby does not take place.
ICSR framework will remove the 30 seconds timer and keep 15 min
periodic timer notification.
Event Based Idle
In this approach an idle second
micro checkpoint is sent from Active to Standby chassis when session changes
from active to idle or vice versa. The micro checkpoint carries the timestamp
when session became active or idle. Upon receipt of the micro checkpoint,
standby chassis updates the active/idle time using the timestamp received in
the micro checkpoint. This process enables the Active and Standby chassis to be
synchronized with respect to when a particular session became active or idle
This approach involves the following processes:
Active chassis sends an idle
second micro checkpoint with timestamp to Standby chassis when a session
Upon receipt of the idlesec micro checkpoint, the Standby chassis
records the timestamp at which session became
When switch over happens, standby uses the timestamp that was
stored to adjust the inactivity time. For example, if session becomes inactive
at time T, and switch over occurs at time T+1000 seconds, standby will set
initial value of the PDN Inactivity timer after subtracting 1000 seconds.
The configuration is available on per APN level to enable this
functionality, and also to configure the duration after which a session is
considered as idle if data is not received or sent.
The default value for this configuration is 180 seconds.
A similar option is provided at ePDG service level in case APN
configuration is not being used on the system. APN configuration overrides the
service level configuration.
Per APN configurations will be done under apn-profile and per
service configurations will be done under ePDG service configuration mode.
The idle timeout configuration under default-subscriber mode
would be retained only for backward compatibility and will have last
The idle second micro-checkpoint timer configuration and the
deemed idle time configuration under subscriber mode will not have any impact
even if configured.
The order of priority of idle timeout configuration would be AAA
received > configured under default-subscriber > configured under
apn-profile > configured under service. However, default-subscriber
configuration is not recommended and should be used only for backward
The order of priority of idle second micro-checkpoint timer
configuration and the deemed idle time configuration would be configured under
apn-profile > configured under service.
When encoding of IDLE second micro checkpoint by ICSR is
successful and just before the checkpoint is to be sent to standby chassis, if
there is a link flap the checkpoint is lost. But anyways the ICSR framework
will again send the same after 15 minutes. If any switch over happens after
flap and within 15 minutes, the transition information is lost.