The relay device includes a first switch interposed between a first extraction unit and a second superimposing unit and a second switch interposed between a second extraction unit and a first superimposing unit. The first switch opens and closes a path where a superimposed signal is relayed from a first transmission path to a second transmission path. The second switch opens and closes a path where a superimposed signal is relayed from the second transmission path to the first transmission path. The first switch is controlled in response to reception of a first control signal to be turned off when a superimposed signal is relayed from the second transmission path to the first transmission path. The second switch is controlled in response to reception of a second control signal to be turned off when a superimposed signal is relayed from the first transmission path to the second transmission path.
1. A relay device which is interposed between a first transmission path and a second transmission path and is used in a communication system allowing communication by use of a first communication signal and a second communication signal superimposed on the first communication signal which are transmitted through the first transmission path and the second transmission path, the relay device comprising:
a first extraction unit configured to extract the second communication signal from a signal transmitted through the first transmission path;
a first shaping unit configured to subject the second communication signal extracted by the first extraction unit, to shaping;
a second superimposing unit configured to superimpose the second communication signal subjected to shaping by the first shaping unit, on the first communication signal on the second transmission path, to send the second communication signal to the second transmission path;
a second extraction unit configured to extract the second communication signal from a signal transmitted through the second transmission path;
a second shaping unit configured to subject the second communication signal extracted by the second extraction unit, to shaping;
a first superimposing unit configured to superimpose the second communication signal subjected to shaping by the second shaping unit, on the first communication signal on the first transmission path, to send the second communication signal to the first transmission path;
wherein:
the relay device further comprises:
a first switch configured to open and close a connection between the first extraction unit and the second superimposing unit; and
a second switch configured to open and close a connection between the second extraction unit and the first superimposing unit,
the first switch is controlled by a first control signal to be turned off when the second communication signal is relayed from the second transmission path to the first transmission path, and
the second switch is controlled by a second control signal to be turned off when the second communication signal is relayed from the first transmission path to the second transmission path, and
wherein:
the relay device further comprises:
a first control unit configured to generate the second control signal according to on the second communication signal extracted by the first extraction unit; and
a second control unit configured to generate the first control signal according to the second communication signal extracted by the second extraction unit.
2. The relay device as set forth in claim 1 , wherein:
the relay device further comprises:
a first judgment unit configured to extract the first communication signal from a signal transmitted through the first transmission path and judge whether or not a current period is a superimposable period in which the second communication signal is allowed to be superimposed; and
a second judgment unit configured to extract the first communication signal from a signal transmitted through the second transmission path and judge whether or not the current period is the superimposable period in which the second communication signal is allowed to be superimposed,
the first control unit is configured to turn off the second switch by the second control signal only while the current period is determined to be the superimposable period by the first judgment unit, and
the second control unit is configured to turn off the first switch by the first control signal only while the current period is determined to be the superimposable period by the second judgment unit.
3. The relay device as set forth in claim 1 , wherein:
the first control unit is configured to turn off the second switch by the second control signal only while the first switch is turned on; and
the second control unit is configured to turn off the first switch by the first control signal only while the second switch is turned on.
4. The relay device as set forth in claim 1 , wherein:
the relay device further comprises:
a first preprocessing unit interposed between the first extraction unit and the first control unit and configured to subject the second communication signal to shaping; and
a second preprocessing unit interposed between the second extraction unit and the second control unit and configured to subject the second communication signal to shaping.
5. The relay device as set forth in claim 4 , wherein:
each of the first preprocessing unit and the second preprocessing unit is configured to generate a pulse signal with a fixed pulse width in response to a trigger defined by a variation in the second communication signal.