The ICSR feature provides the highest possible availability for continuous call processing without interrupting subscriber services. ICSR allows the operator to configure gateways for redundancy purposes. In the event of a gateway failure, ICSR allows sessions to be transparently routed around the failure, thus maintaining the user experience. ICSR also preserves session information and state.
The system supports ICSR between two instances that support ICSR in the same StarOS release. For combination VMs where more than one service type is in use, only those services that support ICSR can make use of ICSR.
ICSR can provide redundancy for site/row/rack/host outages and major software faults. The two instances must be run on non-overlapping hosts and network interconnects. ICSR is only supported between identically configured VPC-DI or VPC-SI instances.
VPC-DI supports both L2 and L3 ICSR.
ICSR is implemented through the use of redundant virtual chassis. The virtual chassis for each VPC-DI instance are configured as primary and backup, with one being active and one standby. Both virtual 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 virtual 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 active CFs in the primary and backup chassis and must be maintained for proper system operation. For additional information, refer to the Session Recovery chapter.
ICSR licenses are currently supported for the following services:
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GGSN Gateway GPRS Support Node
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P-GW Packet Data Network Gateway
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S-GW Serving Gateway
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SAE-GW System Architecture Evolution Gateway
L2TP Access Concentrator (LAC) functionality for ICSR is supported by the following protocol and services:
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eGTP enhanced GPRS Tunneling Protocol
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GGSN Gateway GPRS Support Node
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P-GW Packet Data Network Gateway
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SAEGW System Architecture Evolution Gateway
L2TP Access Concentrator (LAC) functionality for ICSR is not supported by the following service:
L2TP Network Server (LNS) functionality for ICSR is not supported by any services.
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ICSR support for LAC requires a separate LAC license, as well as an Inter-Chassis Session Recovery license.
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Contact your Cisco account representative to verify whether a specific service supports ICSR as an option.
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