Which component provides SRST functionality at a remote site?

• A. Cisco ISR Gateway
• B. Cisco Unified Border Element
• C. Cisco Expressway Edge
• D. Cisco ASA firewall

Answer: (A)

Survivable Remote Site Telephony is provided by the router at the remote site, specifically the Cisco Integrated Services Router (ISR) acting as the local call-processing gateway. When the link to the central call manager (CUCM) is up, phones register and are processed by the central system. If the WAN link goes down, SRST on the ISR takes over so basic call processing can continue locally—allowing internal calls, hold, transfer, and other essential features to function until connectivity is restored. This behavior is why the ISR gateway is the correct component for SRST at a remote site.

The other devices serve different roles: a border element (CUBE) handles voice connectivity to external trunks, not remote-site survivability; Expressway Edge focuses on collaboration-edge access and federation; and the ASA firewall provides security—not call processing.