Which device enables an off-site desktop PC to access a building automation system, or allows the building automation system to dial in to the off-site PC?

• A. A modem to dial in to a building automation system.
• B. A router that assigns IP addresses.
• C. A switch that connects devices.
• D. A firewall that blocks unauthorized access.

Answer: (A)

Remote access over a telephone line is enabled by a modem. A modem converts the computer’s digital signals into analog signals for the phone network and then converts the incoming analog signals back to digital for the computer, letting an off-site desktop dial into the building automation system or letting the BAS dial out to the remote PC. Routers and switches handle network connectivity and data routing within or between networks but don’t provide the dialing-in capability. A firewall protects access and enforces security, but it isn’t the device that makes the remote connection by itself. So, the device that enables this kind of remote dial-in access is a modem.