Cisco Cisco Packet Data Gateway (PDG)
Interchassis Session Recovery
▀ Overview
▄ ASR 5500 System Administration Guide, StarOS Release 16
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Overview
The ICSR feature provides the highest possible availability for continuous call processing without interrupting
subscriber services. ICSR allows the operator to configure geographically distant gateways for redundancy purposes. In
the event of a node or gateway failure, ICSR allows sessions to be transparently routed around the failure, thus
maintaining the user experience. ICSR also preserves session information and state.
subscriber services. ICSR allows the operator to configure geographically distant gateways for redundancy purposes. In
the event of a node or gateway failure, ICSR allows sessions to be transparently routed around the failure, thus
maintaining the user experience. ICSR also preserves session information and state.
ICSR is implemented through the use of redundant chassis. The chassis are configured as primary and backup, with one
being active and one standby. Both chassis are connected to the same AAA server. A checkpoint duration timer controls
when subscriber data is sent from the active chassis to the standby chassis. If the active chassis handling the call traffic
goes out of service, the standby chassis transitions to the active state and continues processing the call traffic without
interrupting the subscriber session.
being active and one standby. Both chassis are connected to the same AAA server. A checkpoint duration timer controls
when subscriber data is sent from the active chassis to the standby chassis. If the active chassis handling the call traffic
goes out of service, the standby chassis transitions to the active state and continues processing the call traffic without
interrupting the subscriber session.
The chassis determine which is active through a proprietary TCP-based connection known as the Service Redundancy
Protocol (SRP) link. The SRP link is used to exchange Hello messages between the primary and backup chassis and
must be maintained for proper system operation.
Protocol (SRP) link. The SRP link is used to exchange Hello messages between the primary and backup chassis and
must be maintained for proper system operation.
ICSR licenses are currently supported for the following services:
eHRPD – Evolved High Rate Packet Data
GGSN – Gateway GPRS Support Node
HA – Home Agent
IPSG – IP Services Gateway
MME – Mobility Management Entity
P-GW – Packet Data Network Gateway
PDSN – Packet Data Serving Node
S-GW – Serving Gateway
Important:
Contact your Cisco account representative to verify whether a specific service supports ICSR as an
option.
Interchassis Communication
Chassis configured to support ICSR communicate using periodic Hello messages. These messages are sent by each
chassis to notify the peer of its current state. The Hello message contains information about the chassis such as its
configuration and priority. A dead interval is used to set a time limit for a Hello message to be received from the
chassis’ peer. If the standby chassis does not receive an Hello message from the active chassis within the dead interval,
the standby chassis transitions to the active state. In situations where the SRP link goes out of service, a priority scheme
is used to determine which chassis processes the session. The following priority scheme is used:
chassis to notify the peer of its current state. The Hello message contains information about the chassis such as its
configuration and priority. A dead interval is used to set a time limit for a Hello message to be received from the
chassis’ peer. If the standby chassis does not receive an Hello message from the active chassis within the dead interval,
the standby chassis transitions to the active state. In situations where the SRP link goes out of service, a priority scheme
is used to determine which chassis processes the session. The following priority scheme is used:
route modifier
chassis priority
MIO/UMIO MAC address