Cisco Cisco Packet Data Gateway (PDG)
Interchassis Session Recovery
Configuring Interchassis Session Recovery (ICSR) ▀
ASR 5500 System Administration Guide, StarOS Release 18 ▄
329
configure
context context_name
service-redundancy-protocol
switchover allow-volte-data-traffic [ maintain-accounting ]
Notes:
When maintain-accounting is enabled, accounting accuracy is maintained for VoLTE calls.VoLTE data is
allowed on the active gateway after VoLTE accounting statistics are flushed.
Graceful Cleanup of ICSR After Audit of Failed Calls
During an Audit on the gateways (P-GW/S-GW/GGSN/SAE-GW) after Session Recovery or an ICSR event, if any
critical information, internally or externally related to a subscriber session seems inconsistent, ICSR will locally purge
the associated session information.
critical information, internally or externally related to a subscriber session seems inconsistent, ICSR will locally purge
the associated session information.
Since external gateways (peer nodes) are unaware of the purging of this session, the UE session may be maintained at
other nodes. This leads to hogging of resources external to the gateway and an unreachable UE for VoLTE calls.
other nodes. This leads to hogging of resources external to the gateway and an unreachable UE for VoLTE calls.
When this feature is enabled, graceful cleanup for an ICSR audit of failed calls occurs. External signaling notifies peers
of session termination before purging the session. The gateway will attempt to notify external peers of the removal of
the session. External nodes to the local gateway include S-GW, P-GW, SGSN, MME, AAA, PCRF and IMSA.
of session termination before purging the session. The gateway will attempt to notify external peers of the removal of
the session. External nodes to the local gateway include S-GW, P-GW, SGSN, MME, AAA, PCRF and IMSA.
Audit failure can occur because of missing or incomplete session information. Therefore, only the peers for which the
information is available will be notified.
information is available will be notified.
The require graceful-cleanup-during-audit-failure Global Configuration mode CLI command enables or disables the
graceful cleanup feature.
graceful cleanup feature.
configure
require graceful-cleanup-during-audit-failure [ del-cause non-ims-apn
{ system-failure | none } ]
{ system-failure | none } ]
Optimization of Switchover Control Outage Time
The ICSR framework minimizes control outage time associated with the flushing of critical full checkpoint statistics,
network convergence and internal auditing.
network convergence and internal auditing.
The amount of time consumed by the following activities affects control outage time during switchover:
Critical Flush – During the Active to Pending-Standby transition, all sessmgrs flush any pending critical FCs
(Full Checkpoints). During this time, the active chassis drops all control packets. If control signaling is allowed
during this stage, a call may get disconnected based on the control message type and accounting information
will be lost.
during this stage, a call may get disconnected based on the control message type and accounting information
will be lost.
Network Convergence – This encompasses the amount of time taken to update routes and send control/data to
the newly active chassis. Control messages are dropped during the transition.
Accounting Flush – During this flush stage data counts are synchronized between chassis. If control signaling is
allowed during this flush, the call may get disconnected based on the control message type, and accounting
information will be lost for calls that existed before switchover.
information will be lost for calls that existed before switchover.
Audit – During audit new calls are not allowed because synchronization of call resources may result in clearing
of the calls.