Chapter 2 1 Interchassis Session Recovery; Overview - Cisco ASR 5500 Administration Manual

Interchassis Session Recovery
This chapter describes how to configure Interchassis Session Recovery (ICSR). The product Administration
Guides provide examples and procedures for configuration of basic services on the system. You should select
the configuration example that best meets your service model, and configure the required elements for that
model as described in the respective product Administration Guide, before using the procedures described
below.
Important
This chapter discusses the following:
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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.
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.
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.
ICSR is a licensed Cisco feature that requires a separate license. Contact your Cisco account representative
for detailed information on specific licensing requirements. For information on installing and verifying
licenses, refer to the Managing License Keys section of Software Management Operations.
Overview, page 269
ICSR Operation, page 274
Configuring Interchassis Session Recovery (ICSR), page 278
Updating the Operating System, page 292
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