, 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 (except its bell) 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 telecommunication circuit in which 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, and may initiate the process of clearing.
See also disconnect supervision.