Abstract: Off-hook initiated demand assignment (OHIDA) has particular application in communications satellite systems and provides basic demand assignment trunk service by utilizing an off-hook and on-hook signal processing system to monitor and control terrestrial access circuits. The signal processing system operates under the control of a central processing unit to interrogate each trunk of line. The detection by a signal scanner of an off-hook condition initiates the call processing sequence. Once the trunks between the originating and terminating terrestrial circuit switches are connected via the satellite circuits, the connected trunks are under the control of the circuit switches throughout the address signalling, the message and the call terminating stages. Call complete detection is performed by a signal scanner to detect an on-hook condition so that the satellite circuit may be disconnected.