| 摘要 |
PURPOSE:To make automatic switching of a communication system efficiently at failures with a simple constitution, by using a carrier detection function, in a data communication system having a duplex system. CONSTITUTION:When a communication line 13a from an MODEM12a1 to an MODEM12a2 is cut off, a carrier detection signal outputted from the MODEM12a2 is turned off, and a changeover device 142 changes over the connection consisting of a data terminal device 112 and the MODEM12b2. Carriers are transmitted from the MODEM12b2, it is detected with the MODEM12b1 and the carrier detection signal outputted from the MODEM12b1 is turned on and a changeover device 141 changes over the connection consisting of a data terminal 111 and the MODEM12b1. As a result, the data terminal devices 111, 112 are automatically connected from the communication system A to the system B. |
