International call progress tones for IP-PBX and VoIP telephony
Telephone Line Signalling
Also known as the Billing pulse or Tax pulse.
Metering pulses are used with payphones and call metering systems for billing purposes.
Unlike 'Pay tones', these signals are intended for the equipment, not for the user, and are an example of out-of-band signalling.
In most countries, a 12 or 16 kHz pulse is sent differentially (~2Vrms/125ms). In a few countries, a common-mode 50 Hz pulse is used (~50Vrms/160ms).
12 kHz is used in Australia, Austria, Cameroon, Central African Republic, Côte d'Ivoire, Denmark, France, Hungary, Iceland, Ireland, Italy, Malta, Portugal, Rwanda, Spain, Sweden, Switzerland, Tunisia & Turkey.
16 kHz is used in Belgium, Bulgaria, Cyprus, Czech Republic, Estonia, Finland, Germany, Greece, Luxembourg, Israel, Lesotho, Norway, Philippines, Poland, Slovakia & Yugoslavia.