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call-number dialing
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On the left, a hand dials a number on a green rotary phone above a graph showing pulses (interruptions in DC current) that represent the phone being dialed. On the right, a hand presses a button on a red tone-dial phone above a representation of a push-button pad showing frequencies corresponding to each button.
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call-number dialing

telecommunications
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On the left, a hand dials a number on a green rotary phone above a graph showing pulses (interruptions in DC current) that represent the phone being dialed. On the right, a hand presses a button on a red tone-dial phone above a representation of a push-button pad showing frequencies corresponding to each button.
Two methods of call-number signaling in a telephone system A major component of any telephone system is signaling. (Left) For telephones with a rotary dial, the design of which became standardized in 1910, each digit is signaled by a corresponding series of pulses, or interruptions, in a direct-current connection between the user's telephone and the local switching office. (Right) In telephones with a push-button pad, each digit is signaled by a “dual tone,” which is made up of two frequencies that correspond to the button's location on the keypad. This type of signaling, which became a worldwide standard starting in the 1960s, is also referred to as tone dialing.

Call-number dialing, also known as direct distance dialing (DDD), refers to the process of directly connecting to a telephone number outside your local calling area without operator assistance. This system uses initial code numbers to establish the connection.1

Historically, this was achieved through rotary dialing, where rotating a dial sent pulses corresponding to the numbers to the switching office. Later, push-button dialing, such as the Touch-Tone system, emerged, offering greater efficiency by using dual-tone multifrequency (DTMF) signals. This system assigns unique tone pairs to each button, allowing for faster and more direct connections.23

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5 Britannica Sources
  1. direct distance dialing
  2. 7 Obsolete Allusions That We Still Use | Dial (verb)
  3. dial telephone
  4. telephone - Rotary dialing
  5. telephone - Push-button dialing

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