International call progress tones for IP-PBX and VoIP telephony
Telephone Line Signalling
Also known as Loop disconnect dialing, Rotary dialing or Decadic dialing.
Pulse dialling is achieved by interrupting the line with bursts of short pulses, with a typical inter-digit delay of 800 ms.
Make/break ratios are 39/61 (US) or 33/67 (Europe), with a nominal rate of 10 pulses per second (pps). In Japan, 20 pps is also used.
In most countries, one pulse is used for the digit 1, two pulses for digit 2, and so on, with ten pulses for the digit 0. Two exceptions are New Zealand, which requires ten pulses for 0, nine pulses for 1, and so on, and Sweden, which requires one pulse for 0, two pulses for 1, and so on.
Nowadays, pulse dialling is superseded by DTMF dialing, however, most equipment retains support for backward compatibility.