What is the term for using two tones to signal switching equipment?

The term for using two tones to signal switching equipment is DTMF, which stands for Dual-Tone Multi-Frequency signaling. This system operates by generating two specific audio tones simultaneously, one from a low-frequency group and one from a high-frequency group, when a button is pressed on a telephone keypad. This dual-tone signaling is widely used in touch-tone dialing and allows for efficient communication to switching equipment, enabling the detection and processing of the signal quickly and accurately.

The use of two distinct frequencies helps differentiate between various keys pressed, which enhances the reliability of the signaling process. DTMF is particularly notable for its application in telephone networks and automated systems, where it facilitates features like call processing, call routing, and interactive voice response systems.