Cisco Cisco Packet Data Gateway (PDG)
Inter-Chassis Session Recovery
▀ Feature Description
▄ SaMOG Administration Guide, StarOS Release 19
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Feature Description
SaMOG is capable of providing chassis-level and geographic-level redundancy and can recover fully created sessions in
the event of a chassis failure.
the event of a chassis failure.
The Cisco ASR 5x00 and virtualized platforms provide industry leading carrier class redundancy. The systems protects
against all single points of failure (hardware and software) and attempts to recover to an operat ional state when multiple
simultaneous failures occur.
against all single points of failure (hardware and software) and attempts to recover to an operat ional state when multiple
simultaneous failures occur.
The system provides several levels of system redundancy:
Under normal N+1 packet processing card hardware redundancy, if a catastrophic packet processing card failure
occurs all affected calls are migrated to the standby packet processing card if possible. Calls which cannot be
migrated are gracefully terminated with proper call-termination signaling and accounting records are generated
with statistics accurate to the last internal checkpoint.
migrated are gracefully terminated with proper call-termination signaling and accounting records are generated
with statistics accurate to the last internal checkpoint.
If the Session Recovery feature is enabled, any total packet processing card failure will cause a packet
processing card switchover and all established sessions for supported call-types are recovered without any loss
of session.
of session.
Even though Cisco provides excellent intra-chassis redundancy with these two schemes, certain catastrophic failures
which can cause total chassis outages, such as IP routing failures, line-cuts, loss of power, or physical destruction of the
chassis, cannot be protected by this scheme. In such cases, the SaMOG Inter-Chassis Session Recovery (ICSR) feature
provides geographic redundancy between sites. This has the benefit of not only providing enhanced subscriber
experience even during catastrophic outages, but can also protect other systems such as the RAN from subscriber
reactivation storms.
which can cause total chassis outages, such as IP routing failures, line-cuts, loss of power, or physical destruction of the
chassis, cannot be protected by this scheme. In such cases, the SaMOG Inter-Chassis Session Recovery (ICSR) feature
provides geographic redundancy between sites. This has the benefit of not only providing enhanced subscriber
experience even during catastrophic outages, but can also protect other systems such as the RAN from subscriber
reactivation storms.
ICSR allows for continuous call processing without interrupting subscriber services. This is accomplished through the
use of redundant chassis. The chassis are configured as primary and backup with one being active and one in recovery
mode. A checkpoint duration timer is used to control when subscriber data is sent from the active chassis to the inactive
chassis. If the active chassis handling the call traffic goes out of service, the inactive chassis transitions to the active
state and continues processing the call traffic without interrupting the subscriber session. The chassis determines which
is active through a propriety TCP-based connection called a redundancy link. This link is used to exchange Hello
messages between the primary and backup chassis and must be maintained for proper system operation.
use of redundant chassis. The chassis are configured as primary and backup with one being active and one in recovery
mode. A checkpoint duration timer is used to control when subscriber data is sent from the active chassis to the inactive
chassis. If the active chassis handling the call traffic goes out of service, the inactive chassis transitions to the active
state and continues processing the call traffic without interrupting the subscriber session. The chassis determines which
is active through a propriety TCP-based connection called a redundancy link. This link is used to exchange Hello
messages between the primary and backup chassis and must be maintained for proper system operation.