Which high-availability design protects against WAN failures at branch sites?

• A. HSRP
• B. VRRP
• C. SRST
• D. GLBP

Answer: (C)

When a branch’s WAN link to the central call-control system fails, you need local call processing to keep basic telephony alive. Survivable Remote Site Telephony runs on the branch router and provides a local, reduced set of call-processing functions, plus a local PSTN gateway path. This lets users make and receive essential calls even when the connection to the central call manager is down. When the WAN is healthy again, normal centralized call control resumes.

Other options focus on keeping data-path gateway availability at the branch, not on preserving telephony control during WAN outages. They don’t guarantee that call processing continues if the link to the central manager is lost. So Survivable Remote Site Telephony is the design that protects against WAN failures at branch sites.