| 摘要 |
PURPOSE:To back up a communication transmission line for signal information with high importance by transmitting the signal information with high importance through an in-use communication transmission line and signal information with low importance through a stand-by communication transmission line, and performing switching to the stand-by communication transmission line when the in-use communication transmission line is disconnected. CONSTITUTION:A communication between telephone sets 4 is allowed through a switchboard 5 by using the in-use communication transmission line 2 as a medium. The stand-by communication transmission line 3 transmits wide-band analog signal information such as TV signal information from the VTR6 of the 1st terminal station A in the order of the 2nd, the 3rd, and the 4th terminal stations B, C and D. When a carrier detecting circuit detects that the in-use voice transmission line 2 has disconnected, a relay is energized to switch the communication transmission line between the telephone sets from the communication transmission line 2 to the communication transmission line 3, which is shared by an image and a voice signal. |
