Q. What do you mean by Dial Pulses?

Dial Pulses: Dial pulsing (many times known as rotary dial pulsing) is the method originally used to transfer digits from a telephone set to local switch. Pulsing digits from a rotary switch began soon after invention of the automatic switching machines. The idea of dial pulsing is quite simple and is depicted in figure. Process begins when telephone set is lifted off hook, completing a path for current through local loop. When switching machine detects off-hook condition, it responds with dial tone. After hearing the dial tone, subscriber begins dial pulsing digits by rotating a mechanical dialling mechanism and then letting it returns to its rest position. As rotary switch returns to its rest position, it outputs a series of dial pulses corresponding to digit dialled.

Whenever a digit is dialled, loop circuit alternately opens (breaks) and closes (makes) a prescribed number of times. Number of switch make/break sequences corresponds to digit dialled (that is the digit 3 produces three switch openings and three switch closers).

Dial pulses take place at 10 make/break cycles per second (which is a period of 100 ms per pulse cycle). For illustration digit 5 corresponds to five make/break cycles lasting a total of 500ms. Switching machine senses and counts the number make/break pairs in sequence.

Break time is nominally 61 ms and make time is nominally 39ms. Digits are separated by idle period of 300 ms called inter digit time. It is important that switching  machine recognize the  inter  digit  time  so  that  it  can  separate  pulses from successive digits. Central office switch incorporates a special timeout circuit to ensure that break part of dialling pulse isn't misinterpreted as phone being returned to its on-hook (idle) condition.