A busy signal (or busy tone or engaged tone) in telephony is an audible call-progress tone or audible signal to the calling party that indicates failure to complete the requested connection of that particular telephone call.
The busy signal has become less common in the past few decades due to the prevalence of call waiting and voicemail.
An otherwise unspecified busy signal indicates that the called number is occupied:
The standard busy signal sometimes occurs (sometimes with an intercept message 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 is used. In some phone companies in the United Kingdom, the busy signal is played after the dial tone 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.
In the mid 1950s through the early 1980s, a telephone busy signal provided an early form of social media in many cities and towns of the United States, colloquially known as the "beep line" or "jam line". [1] [2] 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 dating. Common phone numbers for this to form were on popular radio station 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.
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.
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 dial tone. Until frequencies began to be standardized in the 1960s, telephone signals varied from telephone exchange to exchange.
The European Telecommunications Standards Institute (ETSI) recommendation for busy tone is a 425 Hz tone at -20dBm 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:
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 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 0.4 s (technically: 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 interruption rate (i.e. 0.75 s on, 0.75 s off).
In telephony, ringdown is a method of signaling an operator in which telephone ringing current is sent over the line to operate a lamp or cause the operation of a self-locking relay known as a drop.
Phreaking is a slang term coined to describe the activity of a culture of people who study, experiment with, or explore telecommunication systems, such as equipment and systems connected to public telephone networks. The term phreak is a sensational spelling of the word freak with the ph- from phone, and may also refer to the use of various audio frequencies to manipulate a phone system. Phreak, phreaker, or phone phreak are names used for and by individuals who participate in phreaking.
A dial tone 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 working and is ready to initiate a telephone call. The tone stops when the first dialed digit is recognized. If no digits are forthcoming, the partial dial procedure is invoked, often eliciting a special information tone and an intercept message, followed by the off-hook tone, requiring the caller to hang up and redial.
A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. This allowed an illicit user, referred to as a "phreaker", to place long-distance calls, without using the network's user facilities, that would be billed to another number or dismissed entirely as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network.
A telephone keypad is a keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number. It was standardized when the dual-tone multi-frequency signaling (DTMF) system was developed in the Bell System in the United States in the 1960s that replaced rotary dialing originally developed in electromechanical switching systems. Because of the installed abundance of rotary dial equipment well into the 1990s, many telephone keypads were also designed to produce loop-disconnect pulses electronically, and some could be optionally switched to produce either DTMF or pulses.
A telephone call or telephone conversation, also known as a phone call or voice call, is a connection over a telephone network between the called party and the calling party. Telephone calls started in the late 19th century. As technology has improved, a majority of telephone calls are made over a cellular network through mobile phones or over the internet with Voice over IP. Telephone calls are typically used for real-time conversation between two or more parties, especially when the parties cannot meet in person.
Call waiting is a telephone service where a subscriber can accept a second incoming telephone call by placing an in-progress call on hold—and may also switch between calls. With some providers it can be combined with additional features such as conferencing, call forwarding, and caller ID. Call waiting is intended to alleviate the need to have more than one telephone line or number for voice communications.
Call forwarding, or call diversion, is a telephony feature of all telephone switching systems which redirects a telephone call to another destination, which may be, for example, a mobile or another telephone number where the desired called party is available. Call forwarding was invented by Ernest J. Bonanno. In North America, the forwarded line usually rings once to remind the customer using call forwarding that the call is being redirected. More consistently, the forwarded line indicates its condition by stutter dial tone. Call forwarding typically can redirect incoming calls to any other domestic telephone number, but the owner of the forwarded line must pay any toll charges for forwarded calls. Call forwarding is often enabled by dialing *72 followed by the telephone number to which calls should be forwarded. Once someone answers, call forwarding is in effect. If no one answers or the line is busy, the dialing sequence must be repeated to effect call forwarding. Call forwarding is disabled by dialing *73. This feature requires a subscription from the telephone company. Also available in some areas is Remote Access to call forwarding, which permit the control over call forwarding from telephones other than the subscriber's telephone. VOIP and cable telephone systems also allow call forwarding to be set up and directed via their web portals.
On analog telephone lines with special services, a flash or register-recall signal is used to control functions on the public telephone exchange, PBX or VoIP ATA.
In telephony, call progress tones are audible tones that provide an indication of the status of a telephone call to the user. The tones are generated by a central office or a private branch exchange (PBX) to the calling party.
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 along the route.
In telephony, a special information tone (SIT) is an in-band international standard call progress tone consisting of three rising tones indicating a call has failed. It usually precedes a recorded announcement describing the problem.
The precise tone plan is a signaling specification for the public switched telephone network (PSTN) in North America. It defines the call-progress tones used for indicating the status and progress of telephone calls to subscribers and operators.
The off-hook 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.
The reorder tone, also known as the fast busy tone, or the congestion tone, or all trunks busy (ATB) tone is an audible call progress tone in the public switched telephone network (PSTN) that is returned to a calling party to indicate that the call cannot be processed through the network.
Ringing 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 cadence similar to a traditional power ringing signal (ringtone), but is usually not played synchronously. Various telecommunication groups, such as the Bell System and the General Post Office (GPO) developed standards, in part taken over by the European Telecommunications Standards Institute (ETSI) and other standards bodies. With modern cell phone and smartphone technology ringing tone can be customized and even used for advertising.
In telecommunication, supervision is the monitoring of a telecommunication circuit for telephony to convey to an operator, user, or a switching system, information about the operational state of the circuit. The typical operational states of trunks and lines are the idle and busy states, seizure, and disconnect. The states are indicated by various electrical signals and electrical conditions depending on the type of circuit, the type of terminating equipment, and the type of intended service.
A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other public and private networks.
A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers.
In telephony, beep lines were improvised conference calls hosted over busy signals, loop-around test tones, or certain automated informational service numbers, active in the United States from the mid-1950s to the mid-1980s. These lines allowed callers to communicate with up to dozens of other people simultaneously, the conversations often punctuated by the busy tone "beep" and accompanying intercept message. Such lines were a consequence of the electromechanical nature of switching equipment within the central offices of the public switched telephone network in widespread use at the time. Some journalists have perceived beep lines as early social networks.
