features FSK and DTMF dual systems, which are data transmission formats that contain caller information. Here, Frequency-shift keying (FSK) is a technique used in this case to transmit discrete digital signals. Additionally, Dual-tone multi-frequency (DTMF) relates to the sounds or tones produced by a phone when the digits are pressed. DTMF is used to communicate user intent, such as the number they desire to dial and to control automated equipment.