Survivable Remote Site Telephony

Basic Configuration

The following configuration example is a simple Survivable Remote Site Telephony (SRST) configuration:

Router(config)#call-manager-fallback
Router(config-cm-fallback)#ip source address 10.1.1.1 port 2000
Router(config-cm-fallback)#max-ephones 30
Router(config-cm-fallback)#max-dn 70 octo-line

The call-manager-fallback global configuration command accesses SRST configuration mode. This command is very similar to the telephony-service configuration command used to access Cisco Unified Communications Manager Express (CUCME) configuration mode.

The IP source address configures the IP address on the router(s) that will be listening for Cisco IP Phone registrations during an SRST event. The IP address used for the source address should be a loopback interface if the router has multiple LAN interfaces. The IP address should be an HSRP virtual IP address if there are multiple routers at the site to provide redundancy.

SRST does not support any phones or directory numbers by default. The max-ephones command configures the expected number of SRST Cisco IP phones. The max-ephones command pre-allocates the necessary amount of DRAM to accommodate the phone registrations on the SRST router. The max-dn command works in a very similar way to the max-ephones command, but allocates DRAM for directory numbers on the Cisco IP phones.

This configuration will allow Cisco IP phones to register to SRST and make calls between each other, but not much more. In the next blog, I will delve deeper into the SRST configuration.

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