On-hook
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In telephony, the term on-hook has the following meanings:
- The condition that exists when a telephone or other user instrument is not in use, i.e., when idle waiting for a call. Note: on-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a switchhook. The weight of the receiver depresses the spring loaded switchhook thereby disconnecting the idle instrument from the telephone line.
- One of two possible signaling states, such as tone or no tone, or ground connection versus battery connection. Note: if on-hook pertains to one state, off-hook pertains to the other.
- The idle state, i.e., an open loop of a subscriber line or PBX user loop.
- An operating state of a communications link in which data transmission is disabled and a high impedance, or "open circuit", is presented to the link by the end instrument(s). Note: during the on-hook condition, the link is responsive to ringing signals.
The act of going on-hook is also referred to as releasing the line or channel.
This article contains material from the Federal Standard 1037C (in support of MIL-STD-188), which, as a work of the United States Government, is in the public domain.
