Specifications

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Cisco Unified Survivable Remote Site Telephony Version 4.0 System Administrator Guide
Setting Up the Network
This chapter describes how to configure your Cisco Unified Survivable Remote Site Telephony (SRST)
router to run DHCP and to communicate with the IP phones during Cisco Unified CallManager fallback.
Note Prior to version 4.0, the name of this product was Cisco SRST.
Note The Cisco IOS Voice Configuration Library includes a standard library preface, glossary, and feature and
troubleshooting documents and is located at
http://www.cisco.com/en/US/products/ps6441/prod_configuration_guide09186a0080565f8a.html.
Contents
• Information About Setting Up the Network, page 39
• How to Set Up the Network, page 40
• Where to Go Next, page 49
Information About Setting Up the Network
When the WAN link fails, the Cisco Unified IP Phones detect that they are no longer receiving keepalive
packets from Cisco Unified CallManager. The Cisco Unified IP Phones then register with the router. The
Cisco Unified SRST software is automatically activated and builds a local database of all Cisco Unified
IP Phones attached to it (up to its configured maximum). The IP phones are configured to query the
router as a backup call-processing source when the central Cisco Unified CallManager does not
acknowledge keepalive packets. The Cisco Unified SRST router now performs call setup and processing,
call maintenance, and call termination.
Cisco Unified CallManager uses DHCP to provide Cisco Unified IP Phones with the IP address of
Cisco Unified CallManager. In a remote branch office, DHCP service is typically provided either by the
SRST router itself or through the Cisco Unified SRST router using DHCP relay. Configuring DHCP is
one of two main tasks in setting up network communication. The other task is configuring the Cisco
Unified SRST router to receive messages from the Cisco IP phones through the specified IP addresses.
Keepalive intervals are also set at this time.