off-hook


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off-hook

[′ȯf ‚hu̇k]
(communications)
The active state (closed loop) of a subscriber or PBX user loop.

off-hook

The state of a telephone line that allows dialing and transmission but prohibits incoming calls from being answered. The phone is off-hook when the handset is lifted off the base of a stationary phone or when Talk is pressed on a portable phone.

The term stems from the days when the handset rested on an actual hook. When it was removed, a spring caused contacts to press together, closing the circuit from the telephone to the switchboard in the central office (CO). When a handset is placed back on the base, it is said to be "on-hook," and the phone can receive a call. See central office.


There Really Was a Hook
The hook on this Kellogg telephone (circa 1899) was attached to a spring. When the handset was removed, the contacts inside completed the circuit between the telephone and the central office.
References in periodicals archive ?
The new TR-127 enables high quality delivery of triple play services by maximizing the interoperability of splitters and in-line filters with xDSL transceivers in an active, dynamic telephony environment, including the previously troublesome on-hook, off-hook, ringing, and ring trip events.
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The system is transparent to all telephony signals, including ring, off-hook, hook-switch flash, and for- ward disconnect.
The GXP285 delivers superior audio quality with its HD handset and speakerphone, supports a number of advanced telephony features including hold, mute, transfer, forward, 3-way conference, XML customization of LCD screen, off-hook auto dial, auto answer, click-to-dial, downloadable ringtones, server redundancy and fail-over support, as well as security protection (SRTP and AES encryption of configuration file).
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When a telephone is answered, an off-hook message is sent back to the originating Central Office Switch.