| 摘要 |
1,130,431. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 20 Dec., 1965 [29 Dec., 1964], No. 53884/65. Heading H4K. In a concentrator system of the kind described in Specification 957,477, which employs two pairs TS0, RS0 and TS1, RS1 as a signalling channel between the remote unit and the control unit at the central office CH3, provision is made for switching the signalling circuits to an alternative channel in the event of failure of the normal channel. The system described includes a PBX which has several lines leading to the remote unit and also has tie-lines connected to another office LT1 available from the central office CH3. When the normal signalling channel fails, switching operations occur at both ends, and at the control unit a repertory dialler is effective to set up connections in turn over two tie-lines via CH3 and LT1 to the PBX and thence over two lines to the remote unit. An alternative signalling channel is thus established, and converters are provided at each end for changing the normal D.C. signals to multifrequency signals. |
