The Session Recovery feature provides seamless failover and reconstruction of subscriber session information in the
event of a hardware or software fault within the system preventing a fully connected user session from being
disconnected.

This feature is also useful for Software Patch Upgrade activities. If session recovery feature is enabled during the
software patch upgrading, it helps to permit preservation of existing sessions on the active PSC during the upgrade
process.

Session recovery is performed by mirroring key software processes (e.g. session manager and AAA manager) within the
system. These mirrored processes remain in an idle state (in standby-mode), wherein they perform no processing, until
they may be needed in the case of a software failure (e.g. a session manager task aborts). The system spawns new
instances of ―standby mode‖ session and AAA managers for each active control processor (CP) being used.

Additionally, other key system-level software tasks, such as VPN manager, are performed on a physically separate
packet processing card to ensure that a double software fault (e.g. session manager and VPN manager fails at same time
on same card) cannot occur. The packet processing card used to host the VPN manager process is in active mode and is
reserved by the operating system for this sole use when session recovery is enabled.

The additional hardware resources required for session recovery include a standby system processor card (SPC) and a
standby packet processing card.

There are two modes for Session Recovery.

Task recovery mode: Wherein one or more session manager failures occur and are recovered without the need

to use resources on a standby packet processing card. In this mode, recovery is performed by using the
mirrored ―standby-mode‖ session manager task(s) running on active packet processing cards. The ―standby-