on-hook

(redirected from On hook)

on-hook

[′ȯn ‚hu̇k]
(communications)
The idle state (open loop) of a subscriber or PBX user loop.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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.
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