Which design enables continued local calling at a remote site during WAN outages?

• A. DNS SRV
• B. CUBE
• C. SRST
• D. NTP

Answer: (C)

Survivable remote telephony is the mechanism that keeps basic local calling working at a remote site when the WAN link to the central call-control system is down. With SRST enabled on the router at the remote site, phones can register locally and the router provides call processing for those extensions, using local trunks to handle intra-site calls and, where configured, outbound calls via a local gateway to the PSTN. This ensures that users at that site can make and receive calls without needing the WAN connection to reach the central CUCM.

DNS SRV would help endpoints discover the appropriate server but doesn’t provide fallback call processing during outages. CUBE handles SIP trunking at network borders but doesn’t supply local call processing if the central controller is unreachable. NTP is about time synchronization and has no impact on call survivability.