telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

, call progress tones are audible tones that provide an indication of the status of a

telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...

to the user. The tones are generated by a central office or a

private branch exchange A business telephone system is a telephone system typically used in business environments, encompassing the range of technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone system differs from ...

(PBX) to the calling party. Telecommunication equipment such as

fax machine Fax (short for facsimile), sometimes called telecopying or telefax (short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other out ...

s and

modem The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...

s are designed to recognize certain tones, such as dial tone and busy tone. The

ITU-T The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

E.180 and E.182 recommendations define the technical characteristics and intended usage of some of these tones. ToneScript is a tone description format that may be used to specify the tone. Many European systems follow the recommendations of the

European Telecommunications Standards Institute The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization operating in the field of information and communications. ETSI supports the development and testing of global technical ...

(ETSI).

Types

* Busy tone (or busy signal) * Comfort tone *

Conference call A conference call (sometimes called an audio teleconference or ATC) is a telephone call in which several people share a telephone line at the same time. The conference call may be designed to allow the called party to participate during the cal ...

tone *Confirmation tone * Congestion tone *

Dial tone A dial tone (dialling tone in the UK) is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is ...

* Disconnect tone *End of three-party service tone ( three-way calling) *Executive override tone * Holding tone *Preemption tone *Queue tone *Recall dial tone *Record tone * Recorder warning tone * Reorder tone * Ringing tone, audible ringing * Ring tone, power ringing *Second dial tone *Special dial tone * Special information tone (SIT) *Stutter dial tone (used as a

message-waiting indicator In telephony, a message-waiting indicator (MWI) is a Telcordia Technologies (formerly Bellcore) term for an FSK-based telephone calling feature that illuminates an LED on selected telephones to notify a telephone user of waiting voicemail mess ...

) *

Zip tone In telephony, a zip tone (also known as a whisper tone or call waiting tone) is a call-progress tone which indicates a new incoming call is either connecting or waiting depending on the application. Unlike a ringtone, which alerts those near a t ...

(or Call waiting tone)

Regional and national standards

National telephone systems define tones to indicate the status of lines, equipment, or the result of calls with special tones. Such tones are generally standardized in each country, and may consist of single or multiple frequencies. Most European countries have harmonised to a system of tones based on a single 425 Hz, while the United States uses a dual-frequency system. Exceptions exist, notably in private networks and on some

voice over IP Voice over Internet Protocol (VoIP), also known as IP telephony, is a set of technologies used primarily for voice communication sessions over Internet Protocol (IP) networks, such as the Internet. VoIP enables voice calls to be transmitted as ...

(VoIP) equipment. In Europe, some countries maintain national exceptions based on established older standards and have not fully adopted ETSI recommendations. The most notable exceptions are found in the U.K. (distinct system of tones see table below), Ireland (British style ringback tone), Italy (non continuous dial tone) and France (tone frequencies at 440Hz). Outside of Europe and North America, tone plans vary from country to country but are usually similar enough to be easily recognised by end users calling from abroad and by automatic dialling equipment, such as fax machines and modems. Many countries have adopted plans similar to those recommended by the ETSI, others have influences from North American or British standards, while some like Japan and Australia are unique to those countries. In many cases, when calling from abroad, busy, reorder and other call failure tones may be played by the local switch. Modern signalling protocols like SS7 send this information digitally; thus only a

ringback tone Ringing tone (audible ringing, also ringback tone) is a signaling tone in telecommunication that is heard by the originator of a telephone call while the destination terminal is alerting the receiving party. The tone is typically a repeated cade ...

or announcement generated by a distant switch in a foreign network will ever be heard by callers from other countries or networks. Mobile phones

roaming Roaming is a wireless Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or oth ...

on a foreign network will often be provided with a ringback tone from the network they are temporarily hosted on. For example, calling a US phone in Europe may return a European ringback tone or vice versa. Increasingly, networks may opt to play their own domestic tones instead, making roaming seamless. In this case the ringing state is sent by the host network and the tone is generated by the home network. In some instances, the tones are entirely generated by the local network or even by the telephone itself; this is increasingly common on VoIP-based services. In this case no distantly generated tones will be heard. The use of signalling protocols rather than audible tones means that a voice channel to the distant switch is unnecessary unless a call is connected. This saves network bandwidth, switch capacity and is often more user friendly as it can provide local tones or even on-screen feedback to end users.

North American tones

The tone frequencies, as defined by the precise tone plan, are selected such that

harmonics In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st harm ...

and

intermodulation Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of Signal (electrical engineering), signals containing two or more different frequencies, caused by non-linear, nonlinearities or time variance in a system. ...

products will not cause an unreliable signal. No frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies. The frequencies were initially designed with a

ratio In mathematics, a ratio () shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...

of 21/19, which is slightly less than a

whole tone In Western music theory, a major second (sometimes also called whole tone or a whole step) is a second spanning two semitones (). A second is a musical interval encompassing two adjacent staff positions (see Interval number for more deta ...

. The frequencies may not vary more than ±1.8% from their nominal frequency, or the switching center will ignore the signal. The high frequencies may be the same volume as – or louder than – the low frequencies when sent across the line. The loudness difference between the high and low frequencies can be as large as 3

decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whos ...

s (dB) and is referred to as "twist." The duration of the tone should be at least 537 ms.Transmitted signaling rate of 93 ms per digit with minimum 40 ms pause between tones. A 40 ms tone should be detected and a 23 ms tone must be rejected.
/ref>

ETSI guidelines (EU)

EU national exceptions to harmonised ETSI

UK tones

Australian tones

Supervisory tones in the Australian PSTN are defined i
AS/CA S002
published by the Communications Alliance.

References

External links

Various Tones Used in National Networks (According to ITU-T Recommendation E.180)
{{Telsigs Telephony signals