SRST stands for Survivable Remote Site Telephony; what is its purpose?

• A. A security mechanism for remote firmware updates.
• B. A cloud-based telephony service for remote offices.
• C. Survivable Remote Site Telephony—provides local call processing if WAN connectivity is lost.
• D. A voice encoding standard for remote sites.

Answer: (C)

SRST provides survivable local call processing at a remote site when the link to the central call-control system is lost. In practice, the router at the remote site takes over signaling and call handling for registered IP phones and local gateways, so users can still make and receive calls (including to the local PSTN) even if the WAN to CUCM is down. When connectivity returns, normal centralized call processing resumes. This is not a security mechanism, cloud service, or a voice-encoding standard.