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Collaboration, Voice & AV · Intermediate

Survivable Remote Site Telephony (SRST)

A Cisco router feature that lets branch phones register locally and keep basic calling when they lose contact with CUCM.

Definition

When a WAN failure prevents phones from reaching their CM Group, they register to the SRST router defined by the SRST reference in the device pool. The router provides basic calling, local PSTN access through its gateway and limited features until CUCM is reachable again, after which phones fall back. Variants include SCCP SRST, SIP SRST, Unified SRST built on CME, and Enhanced SRST, which syncs configuration from CUCM.

Example

voice register global / mode srst and the SRST reference in DP-Branch allow SIP phones to register to the branch ISR.

Exam tip

SRST is defined on the device pool through the SRST reference; MGCP gateways need fallback configuration for the PSTN path.

Related terms