Dial tone

dial-tonedialling tonestutter dial tonetone
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.wikipedia
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Telephone exchange

exchangescentral officeexchange
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.
In North America, a central office location may also be identified as a wire center, designating a facility from which a telephone obtains dial tone.

Telephone call

callphone callphone calls
It indicates that the exchange is working and is ready to initiate a telephone call.
Otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number.

Special information tone

special information tonesOOS
If no digits are forthcoming, the permanent signal 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.
Like a dial tone or busy signal, the SIT is an in-band signal intended both to be heard by the caller, and to be detected by automated dialing equipment to determine a call has failed.

Off-hook tone

high toneHowler toneHowler/off-hook warning
If no digits are forthcoming, the permanent signal 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.
It is played between the dial tone timeout recording ("If you would like to make a call...") and the permanent signal holding state.

Call forwarding

forwardingCall divertCall Forward on Busy
It may serve as a message-waiting indicator for voice mail, or indicate that a calling feature, such as call forwarding has been activated.
More consistently, the forwarded line indicates its condition by stutter dial tone.

Message-waiting indicator

Message Waiting IndicationMessage waiting indicationsMessage Waiting Indicator
It may serve as a message-waiting indicator for voice mail, or indicate that a calling feature, such as call forwarding has been activated.
VMWI differs from existing features that use other message indicators, such as audible stuttered dial tone, in that it activates a visual indicator on the CPE.

Precise tone plan

The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, appear to have a modulation at 90 Hz.

Rotary dial

rotary telephonedialrotary phone
When he picked up his own household phone, his assistant had to explain what the strange noise was, as well as show Eisenhower how to use a rotary dial phone.

Busy signal

busy toneengaged tonebusy
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.

Telephony

digital telephonytelephonedigital
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.

Signaling (telecommunications)

signalsignalingout-of-band signaling
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.

On- and off-hook

off-hookon-hookon hook
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.

Permanent signal

left off-hookpermanent loop
If no digits are forthcoming, the permanent signal 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.

Intercept message

recorded announcementrecordingerror messages
If no digits are forthcoming, the permanent signal 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.

Switchboard operator

telephone operatoroperatortelephonist
Early telephone exchanges signaled the switchboard operator when a subscriber picked up the telephone handset to make a call.

Hildesheim

Hildesheim, GermanyHimmelsthürHI
Invented by engineer August Kruckow, the dial tone was first used in 1908 in Hildesheim, Germany.

Western Electric

Western Electric CompanyWestrexWestern Electric Manufacturing Company
The Bell Telephone Manufacturing Company (BTMC) in Antwerp, Belgium, Western Electric's international subsidiary, first introduced dial tone as a standard facility with the cutover of the 7A Rotary Automatic Machine Switching System at Darlington, England, on 10 October 1914.

Dwight D. Eisenhower

Dwight EisenhowerEisenhowerPresident Eisenhower
By the time President Dwight D. Eisenhower retired in 1961 it was nearly universal, but the president himself had never encountered a dial tone.

Electromechanics

electromechanicalelectro-mechanicalElectromechanical Engineering
Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators.

Motor–generator

double-acting electric motorselectric motorselectric motor
Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators.

Vibrator (electronic)

vibratorelectromechanical vibratorVibrator power supply
Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators.

Hertz

MHzkHzHz
In the United States, the standard "city" dial tone was a 600 Hz tone that was amplitude-modulated at 120 Hz.

North American Numbering Plan

Area codeArea codesArea code(s)
The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, appear to have a modulation at 90 Hz.

United States

AmericanU.S.USA
The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, appear to have a modulation at 90 Hz.