A busy signal (or busy tone or engaged tone) in

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is an audible call-progress tone or audible

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to the calling party that indicates failure to complete the requested connection of that particular

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 ...

. The busy signal has become less common in the past few decades due to the prevalence of call waiting and

voicemail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows callers to leave a recorded message when the recipient has been unable (or unwilling) to answer the phone. Calls may be directed to voicemail m ...

Reasons for a busy signal

An otherwise unspecified busy signal indicates that the called number is occupied: * The called number is talking with another caller on the phone * The number is calling out * Someone else has called the number or is calling the number at the same time * The other line was left off-hook * It is otherwise unavailable The standard busy signal sometimes occurs (sometimes with an

intercept message An intercept message is a telephone recording informing the caller that the call cannot be completed, for any of a number of reasons ranging from local congestion, to disconnection of the destination phone, number dial errors or network trouble a ...

played over the busy) at the end of a call to indicate the other party has hung up (see Disconnect tone), but mostly the

off-hook tone The off-hook tone (also off-hook warning, howling tone, or howler tone) is a telephony signal for alerting a user that the telephone has been left off-hook without use for an extended period, effectively disabling the telephone line. North Ame ...

is used. In some phone companies in the United Kingdom, the busy signal is played after the

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 ...

to indicate the caller has used up their allocated time to dial a number and must hang up, before the off-hook tone is played.

The "beep line"

In the mid 1950s through the early 1980s, a telephone busy signal provided an early form of

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in many cities and towns of the United States, colloquially known as the " beep line" or "jam line". Due to a flaw in the telephone switching equipment, teenagers discovered they could talk to each other over the busy signal, often exchanging phone numbers, mostly for the purpose of

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. Common phone numbers for this to form were on popular

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request lines, where teens would be calling in en masse to try to win concert tickets or request their favorite songs, thus "jamming the lines" and generating a perpetual busy signal.

Reorder tone

A reorder tone, sometimes called a ''fast busy'' signal, indicates that no transmission path to the called number is available. This can occur either because the Inter-LATA trunk is busy at the time of the call- in which case this clears in a few seconds, if one redials- or the number is temporarily out of service, due to maintenance or the number is not willing to accept calls. It is otherwise played after a recorded announcement explaining the reason for a general call failure.

Styles

Countries have different signaling tones that act as busy signals, in most cases consisting of a tone with equal on/off periods at a rate of between 60 and 120 interruptions per minute (i.p.m.). In North America, the Precise Tone Plan used today employs two tones of 480 and 620 Hz at an amplitude of -24 dBm with a 0.5 s on/off cadence. Prior to the adoption of the PreciseTone system, the busy signal generally had the same frequency as the

. Until frequencies began to be standardized in the 1960s, telephone signals varied from telephone exchange to exchange. 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) recommendation for busy tone is a 425 Hz tone at -20 dBm in a 0.5 s on/off cadence. This sequence was already in use in Portugal, Spain, The Netherlands, (West-)Germany, Italy, Greece, Switzerland, Lichtenstein, Iceland, Norway, Andorra, Monaco, San Marino, and Vatican City prior to publication of the ETSI recommendation. The ETSI recommendation is now followed by all countries of the European Union. Historical oddities within the EU are: *

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follows the ETSI recommendation for the busy tone, but the ringback tone is the same as that used in the UK. * A few networks in France continue to use a 440 Hz/0.5 s sequence in place of the ETSI recommended 425 Hz/0.5 s sequence, but this is gradually being replaced. The ETSI recommendation is also the default (i.e. non-localized) busy tone generated by mobile phones that follow the GSM & 3GPP family of standards. The ETSI recommendation is also followed by some

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

equipment and PBX/office systems found outside Europe. Most countries of the former Soviet Union, including Russia, are not members of the ETSI. These former Soviet republics employ a 425 Hz busy tone with a 0.4 s on/off cadence. In the United Kingdom, the busy tone is a single 400 Hz tone with equal 0.375 s on/off periods. This was the case even when the UK was still part of the EU. The current 400 Hz/375ms tone was adopted in the mid-to-late 1960s and replaced the older busy tone, which was the same 400 Hz signal but at half the pulse duration, 0.75 s on, 0.75 s off.

References

External links

ETSI Listing and analysis of European, World and Standardized tones

Jam Line

Busy Signal Chat Rooms
{{DEFAULTSORT:Busy Signal Telephony signals