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 ?
Here's the issue: Because off-hook agents maintain an open SIP stream to particular gateways, in a multi-gateway deployment you need to understand how a call received on one gateway can be routed to an agent connected off hook to another gateway.
The wetting current mainly addresses all-digital services, unlike services with underlying POTS (Plain Old Telephone Service) that inherently provide loop current while off-hook.
This chipset keeps the rich set of features supported in previous EZDAA family chipsets such as Caller ID, DTMF, continuous line-in-use monitoring, line voltage and loop-current monitoring, line reversal detection for both on- and off-hook and programmable ring detection threshold.
Handset/headset choice, off-hook dialing, hands-free use (not supported in analog CO mode), and ring tones (different for IP and analog lines).