The active state of a customer telephone circuit. The term is derived from old telephone sets where the receiver, when not in use, was placed on a hook attached to a switch. The opposite condition is off-hook.
A telephone that is resting on its cradle. BX (Private Branch eXchange) A small to medium sized customer premise telephone system that is also a switch (computer) providing communications between onsite telephones and exterior communications networks. PBX systems are connected to the CO with trunks. On a PBX, an outside line is normally accessed by dialing "9."
When a modem goes on-hook, it releases the telephone line to which it is connected, freeing the telephone line for other uses. This action, which is equivalent to hanging up a telephone, terminates the current data connection.