Telecommunications

There are two ways to dial a telephone number. Both ways accomplish the same goal: to send a signal to the central office that we want to be connected to that number.
The first way is rotary or pulse dialing (rotary dialing was patented in 1923 by Frenchman Antoine Barnay). This method of dialing sends a signal to open and close a switch at the end of a local loop at a fixed rate of speed. These pulses are translated into numbers by “counting” the number of 1/10-second breaks.
Dual Tone Multi-frequency (DTMF) is different in that the number is dialed by sending a specific dual-frequency tone assigned to each number. That assignment is determined by a grid. The different high frequency tones (three) are assigned to the columns on a telephone keypad, while the different low frequency tones...