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Information about Off Hook

In telephony, the term off-hook has the following meanings:
  1. The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece (i.e., receiver), which hung from its switchhook until the user wished to activate it. The weight of the receiver no longer depresses the spring loaded switchhook, thereby connecting the instrument to the telephone line.
  2. One of two possible signaling states, such as tone or no tone and ground connection versus battery connection. Note that if off-hook pertains to one state, on-hook pertains to the other.
  3. The active state, i.e., a closed loop of a subscriber line or PBX user loop.
  4. An operating state of a communications link in which data transmission is enabled either for (a) voice or data communications or (b) network signaling.


Source: from Federal Standard 1037C and from MIL-STD-188

On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair. When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a permanent loop or permanent signal.

The act of going off-hook is also referred to as seizing the line or channel.

See also

In telecommunication, telephony (IPA pronunciation: [tə'lɛfəˌni]) encompasses the general use of equipment to provide voice communication over distances, specifically by connecting telephones to each other.
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The telephone is a telecommunications device which is used to transmit and receive sound (most commonly speech). Most telephones operate through transmission of electric signals over a complex telephone network which allows almost any phone user to communicate with almost anyone.
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In telecommunications, a user is a person, organization, or other entity that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information.
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Dial may mean:
  • Dial (of telephone), a device for the input of numbers in telephones and similar devices
  • A 'sundial' and/or 'clock dial'
  • Dial, a person's face; slang; v., e.g., P.G.

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Headphones (also known as earphones, earbuds, stereophones, headsets, or by the slang term cans) are a pair of tiny loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them
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worldwide view.
For the Electric Light Orchestra song, see .
A telephone line or telephone circuit (or just line or circuit within the industry) is a single-user circuit on a telephone communications system.
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In telecommunication, signalling (UK spelling) or signaling (US spelling) has the following meanings:
  • The use of signals for controlling communications.

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Ground may refer to:
  • The surface of the Earth
  • Soil, a mixture of sand and organic material present on the surface of the Earth
  • Ground (electricity), in electrical engineering, something that is connected to the Earth or at the voltage defined as zero (in the U.S.

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An electrical connection between discrete points allows the flow of electrons, (current). A pair of connections is needed for a circuit.

Between points with a low voltage difference between them, direct current flow can be controlled by a switch.
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In telephony, the local loop (also referred to as a subscriber line) is the physical link or circuit, that connects from the demarcation point of the customer premises to the edge of the carrier, or telecommunications service provider, network.
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Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public.
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For other uses, see Data (disambiguation).


Debt, AIDS, Trade in Africa (or DATA) is a multinational non-government organization founded in January 2002 in London by U2's Bono along with Bobby Shriver and activists from the Jubilee 2000 Drop
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In telecommunications, transmission is the forwarding of signal traffic over distances that are too great to be simply connected by a twisted pair wires. Techniques available now may be microwave link, satellite link, coaxial cable or fibre optic cable.
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A telecommunications network is a of telecommunications links and nodes arranged so that messages may be passed from one part of the network to another over multiple links and through various nodes.
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In telecommunication, signalling (UK spelling) or signaling (US spelling) has the following meanings:
  • The use of signals for controlling communications.

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Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended.
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MIL-STD-188 is a series of U.S. military standards relating to telecommunications.

Purpose

Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of
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worldwide view of the subject.
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In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls.
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Permanent Signal (PS) in US telephony jargon, or Permanent Loop in British usage, is a condition in which a POTS line is off-hook for an extended period of time. This is indicated in modern switches by the silent termination after the off hook tone times out and the
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The off-hook tone (also receiver off-hook tone or off-hook warning) is a telephony signal used to alert a user that the telephone has been accidentally left off-hook for an extended period, effectively disabling the telephone line. See permanent signal.
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Hook Flash is a button on a telephone that simulates a quick off-hook/on-hook/off-hook cycle. Usually the functional equivalent of quickly hanging up and lifting the receiver on a middle 20th century cradle phone. Many modern telephones implement this function as a button.
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