Dial pulsing is a method of transmitting dialled digits to the telco in circumstances where you are unable or unwilling to send DTMF signals. The signal is sent by simulating the on-hook condition (breaking the loop) and restoring the off-hook condition (making the loop) a given number of times depending on the digit dialled.
In the North American standard, a pulse rate of ten pulses per second with an break/make ratio of 60% is prescribed. So, to dial a '2', the circuit must be broken for 60 milliseconds, remade for 40 milliseconds, broken for another 60 milliseconds, and then restored for at least half a second so that the telco's switching equipment can know that the digit is finished transmitting. This timing is why impatient people to try to speed up the movement of a rotary dial often have difficulty getting their calls to go through properly.
60ms
~21mA __ v _ _ _ ______ ______ ______
Current | | | | | | | | | | | | |
~0mA __| |_| |_| |_| |_| ^ |_| |_|
Dial ^ Interdigital
Tone 40ms Pause
{ Digit 4 } {1} {1}
That is a reasonable approximation of the signal as it leaves the telephone. It should be noted, however, that reactive components within the loop will 'smear' the wave as it is being transmitted to the telco's switch.