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 system is transparent to all telephony signals, including ring, off-hook, hook-switch flash, and for- ward disconnect.
And, because a silicon data access arrangement (DAA) is used, off-hook and parallel phone detection is supported.
While most mainstream vendors are not challenged by this requirement, buyers need to be sure their proposed solution can, in fact, support multiple gateways and off-hook agents without "tromboning" or "doglegging" calls (i.e., "hard bridging" calls across gateways).
Lines and trunks were monitored for service requests such as an "off-hook" or "circuit busy," dialed numbers were "looked up" in a register, and circuits were established sequentially from switch to switch across the network.