Q. Explain about Dial Pulses?

Dial pulsing (sometimes known as rotary dial pulsing) is the method basically used to transfer digits from a telephone set to the local switch. Pulsing digits from a rotary switch began soon after invention of the automatic switching machines. Concept 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 the local loop. When switching machine detects off-hook condition, it responds with dial tone. After hearing the dial tone, subscriber begins the dial pulsing digits by rotating a mechanical dialing 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 dialed. Whenever a digit is dialed, loop circuit alternately opens (breaks) and closes (makes) a prescribed number of times. Number of switch make/break sequences corresponds to digit dialed (which is the digit 3 produces three switch openings and three switch closers). Dial pulses take place at 10 make/break cycles per second (it implies that 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 number make/break pairs in the sequence.