Which of the following is true about remotely controlling building systems over dial-up lines?

• A. DTMF signaling can be used for this purpose.
• B. Infrared is typically used for dial-up control.
• C. Bluetooth is the standard for dial-up control.
• D. Wi-Fi is used for dial-up control.

Answer: (A)

Remote dial-up control relies on signaling that travels over the telephone network, so DTMF tones are a natural fit. DTMF uses the keypad tones generated at the caller and decoded by the receiving system, allowing commands to be sent over a voice-grade line during a phone call. This makes it well suited for dial-up connections, which ride on the public switched telephone network without needing a separate data link.

Infrared is a line-of-sight, short-range method designed for local device control and isn’t carried over phone lines. Bluetooth and Wi‑Fi are wireless data technologies intended for local networks or short-range internet access and require different network infrastructure than dial-up lines. They aren’t standard for dial-up remote control.