on-hook

In telephony, the condition that exists when an operational telephone, or other user instrument, is not in use. Note: On-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a hook that extended from a vertical post that supported the microphone also. The hook was mechanically connected to a switch that automatically disconnected the idle telephone from the network. 2. 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. 3. The idle state, i.e., open loop, of a subscriber or PBX user loop. 4. An operating state of a communications link in which data transmission is disabled and a high-impedance, i.e., 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. See on-hook state.