JPH0750616A - Line switching control circuit - Google Patents

Abstract

PURPOSE:To provide the interface part of an in-use line and the interface part of a standby line with the same internal constitution and to unnecessitate an exclusive control part in a communication equipment for making one standby line correspond to the optional pieces of the in-use lines and switching the in-use lines to the standby line. CONSTITUTION:When a fault is detected inside the interface part 1, the interface part 1 outputs an interface part fault detection signal (c) to the interface part 2. The interface part 2 detects the generation of the fault inside the interface part 1 by the input of the interface part fault detection signal (c) and outputs that the fault is generated in the interface part 1 to the interface part 3 by a fault interface part number (d.) The interface part 3 detects that the fault is generated in the interface part 1 by the input of the fault interface part number (d) and processes the line processed by the interface part 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line switching control circuit, and more particularly to a line switching control circuit in the case where one protection line is associated with an arbitrary plurality of working lines.

[0002]

2. Description of the Related Art Conventionally, a line switching control circuit of this kind has been used in a synchronous multiplexer for switching a working line in which a failure has occurred to a protection line. An example of a conventional line switching control circuit is Fiber Network Survivability, pp. 76-82 (Fiber
Network Survivability, P76
~ P82). FIG. 3 is a block diagram showing an example of a conventional line switching control circuit when there are two working lines and one protection line. The interface unit 21 receives the reception signal a ₁₅ from the working line 29 and transmits the transmission signal b ₁₀
Is output to the working line 29. The switching circuit 24 inputs the reception signal a ₁₈ from the interface unit 21 and outputs the reception signal a ₂₀ to the device side. The switching circuit 25 inputs the transmission signal b ₁₅ from the device side and outputs the transmission signal b ₁₃ to the interface unit 21. The interface unit 22 inputs the reception signal a ₁₆ from the working line 30 and outputs the transmission signal b ₁₁ to the working line 30.

The switching circuit 26 is the interface unit 2.
The received signal a ₁₉ is input from 2 and the received signal a ₂₁ is output to the device side. The switching circuit 27 sends the transmission signal b ₁₆ from the device side.
To output the transmission signal b ₁₄ to the interface unit 22. The interface unit 23 receives the reception signal a ₁₇ from the protection line 31 and switches the protection reception signal P to the switching circuit 24.
To the switching circuit 26, and the switching circuit 25
Alternatively, the spare transmission signal Q is input from the switching circuit 27 and the transmission signal b ₁₂ is output to the spare line 31. The switching control circuit 28 receives the switching control communication reception signal r from the interface unit 23, outputs the switching control communication transmission signal s to the interface unit 23, and outputs the switching control signal t to the switching circuits 24 and 25 to perform switching. The switching control signal u is output to the circuits 26 and 27. The reception signal failure detection circuit 32 outputs the reception signal failure detection signal v to the switching control circuit 28. Received signal fault detection circuit 33
Outputs the reception signal failure detection signal w to the switching control circuit 28. The reception signal failure detection circuit 34 outputs the reception signal failure detection signal x to the switching control circuit 28.

Next, with respect to the operation of the conventional line switching control circuit shown in FIG. 3, a specific operation in the case of two working lines and one protection line will be described. First, the working line 29
The interface unit 21 corresponds to, the working line 30 corresponds to the interface unit 22, and the protection line 31 corresponds to the interface unit 23. When the working system is normal, the interface section 21 uses the working line 29.
The contents of the received signal a ₁₅ from the communication line are output to the switching circuit 24 as the received signal a ₁₈ , and the interface unit 22 outputs the contents of the received signal a ₁₆ from the working line 30 to the switching circuit 26 as the received signal a _19. The unit 23 outputs the content of the reception signal a ₁₇ from the protection line 31 to the switching circuits 24 and 26 as the protection reception signal P. The switching control circuit 28 connects the switching circuits 24 and 25 to the working line 2
9 outputs a switching control signal t indicating that it corresponds to 9,
A switching control signal u indicating that it corresponds to the working line 30 is output to the switching circuits 26 and 27.

The switching circuit 24 outputs the content of the received signal a _{18 to} the device side as a received signal a ₂₀ . Switching circuit 2
5 outputs the content of the transmission signal b ₁₅ input from the device side to the transmission signal b ₁₃ and outputs nothing to the preliminary transmission signal Q. The switching circuit 26 changes the content of the received signal a ₁₉ to the received signal a ₂₁
Is output to the device side. The switching circuit 27 outputs the content of the transmission signal b ₁₆ input from the device side to the transmission signal b ₁₄ and outputs nothing to the preliminary transmission signal Q. The interface unit 21 outputs the content of the transmission signal b _{13 to} the working line 29 as the transmission signal b ₁₀ . The interface unit 22 outputs the content of the transmission signal b _{14 to} the working line 30 as the transmission signal b ₁₁ . The switching control circuit 28 outputs the switching control communication transmission signal s to the interface unit 23, and the interface unit 23 inserts the switching control communication transmission signal s into the transmission signal b ₁₂ and outputs it to the protection line 31. The interface unit 23 outputs the switching control communication reception signal r extracted from the reception signal a ₁₇ to the switching control circuit 28.

As a result, the switching control circuit 28 uses the protection line 31 to perform switching control communication with the opposite station, and exchanges fault line information and a line switching request and permission. When a failure occurs in the reception signal a ₁₅ of the working line 29, the reception signal failure detection circuit 32 detects the failure occurrence of the reception signal a ₁₅ , and the reception signal failure detection signal v
Is notified to the switching control circuit 28. The switching control circuit 28 sends a request for switching the working line 29 to the protection line to the opposite station by the switching control communication transmission signal s. Then, when the switching control communication reception signal r indicating permission of switching from the opposite station is input to the switching control circuit 28, the switching control circuit 28 outputs the switching control signal t corresponding to the protection line to the switching circuits 24 and 25. . The switching circuit 24 outputs the content of the preliminary reception signal P as the reception signal a ₂₀ .

As a result, the content of the received signal a ₁₇ received by the interface section 23 from the protection line 31 becomes the received signal a ₂₀ . The switching circuit 25 outputs the content of the transmission signal b _{15 to} the interface unit 23 as the preliminary transmission signal Q. As a result, the content of the transmission signal b ₁₅ sent from the device side becomes the transmission signal b ₁₂ on the protection line 31. By the above operation, the working line 29 is switched to the protection line 31. When the received signal a ₁₆ of the working line 30 has a failure, the working line 30 is switched to the protection line 31 as in the case of the received signal a ₁₅ having a failure. When a failure occurs in the reception signal a ₁₇ of the protection line 31, the reception signal failure detection circuit 34 detects the failure occurrence of the reception signal a ₁₇ and notifies the switching control circuit 28 by the reception signal failure detection signal x. This switching control circuit 2
8 recognizes that the protection line 31 is unavailable,
After that, even if a failure occurs in the working line 29 or the working line 30, the protection line is not switched.

[0008]

In this conventional line switching control circuit, switching control from the working line to the protection line is performed by centralized control by one switching control circuit, so input / output with the line is performed. It is necessary to separately provide a switching control unit in addition to the interface unit in the part, which causes a problem that the configuration becomes complicated and the device becomes large. The present invention has been made to solve such a problem, and an object thereof is to realize a line switching control circuit that does not require a dedicated control unit by realizing an interface unit of a working line and an interface unit of a protection line with the same internal configuration. And

[0009]

A line switching control circuit according to the present invention includes a switching circuit for inputting a received signal from a line side, a switching circuit for inputting a transmission signal from a device side, and a failure of a received signal from the line. Received signal failure detection circuit to detect, and the failure interface section number and interface section failure detection signal are input from the interface section adjacent to one side, the failure interface section number is output to the interface section adjacent to the other side, and switching control to both switching circuits is performed. A switching control circuit for outputting a signal, a switching control circuit fault detection circuit for inputting a fault monitoring signal from the switching control circuit, and a switching control circuit fault detection circuit for inputting a received signal fault detection signal from the received signal fault detection circuit Input the switching control circuit failure detection signal from the And OR gate which outputs to the interface portion adjacent to the circuit and the other switches the detection signal, and a gate to be output to the device side ORs enter the received signal from the switching circuit in a plurality of interface units to the line interface.

[0010]

In the present invention, the interface section inputs the interface section failure detection signal and the failure interface section number from the interface section adjacent to one side, and inputs the interface section failure detection signal and the failure interface section number to the other adjacent interface section. Is output, and if the interface part corresponds to the working line, the interface part in which a failure has occurred is detected by inputting the interface part failure detection signal and the failed interface part number, and a failure has occurred in the interface part adjacent to the other The failure interface part number indicating the interface part is output. When the interface unit corresponds to the protection line, the interface unit in which the failure has occurred is detected by inputting the interface unit failure detection signal and the failed interface unit number.

[0011]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a line switching control circuit according to the present invention, and shows an example when the present invention is applied to the case of two working lines and one protection line. In FIG. 1, reference numerals 1, 2 and 3 denote interface units, which receive the received signal a ₃ from the working line 6 and the transmitted signal b ₁ from the device side, and use the working line 6 respectively.
The transmission signal b ₃ is output to. The interface unit 2 receives the interface unit failure detection signal c from the interface unit 1 and the received signal a ₄ from the working line 7,
The transmission signal b ₂ is input from the device side, and the transmission signal b ₄ is output to the working line 7. The interface unit 3 is the protection line 8
Received signal a ₅ from the device side, transmitted signal b ₁ and transmitted signal b ₂ from the device side, and output transmitted signal b ₅ to the protection line 8, and the interface section 2 has a failure interface number d and an interface failure. The detection signal e is input. The OR gate 4 inputs the reception signal a ₆ from the interface unit 1 and the reception signal a ₇ from the interface unit 3, takes the logical sum and outputs it as the reception signal a ₁ to the device side. The OR gate 5 inputs the reception signal a ₈ from the interface unit 2 and receives the reception signal a ₉ from the interface unit 3.
Is input and the logical sum is output as the received signal a ₂ to the device side.

FIG. 2 is a block diagram showing a configuration example of the interfaces 1, 2 and 3 in FIG. This Figure 2
In FIG. 1, the same reference numerals as those in FIG. 1 indicate corresponding portions, and the receiving circuit 9 inputs the received signal a ₁₀ from the line. The switching circuit 13 inputs the reception signal a ₁₁ from the reception circuit 9 and outputs the reception signals a ₁₂ and a ₁₃ . The switching circuit 14 inputs the transmission signals b ₁ and b ₂ from the device side. The transmission circuit 11 inputs the transmission signal b ₉ from the switching circuit 14 and outputs the transmission signal b ₈ to the line. The reception signal fault detection circuit 10 inputs the reception signal a ₁₀ from the line. The switching control circuit 15 inputs the switching control communication reception signal i from the receiving circuit 9,
The failure interface number f and the interface failure detection signal g are input from the adjacent interface section, the switching control communication transmission signal j is output to the transmission circuit 11, and the switching control signal h is output to the switching circuits 13 and 14. The failure interface part number n is output to the interface part adjacent to the other. The switching control circuit fault detection circuit 12 receives the fault monitoring signal k from the switching control circuit 15. The OR gate 16 inputs the reception signal failure detection signal l from the reception signal failure detection circuit 10 and the switching control circuit failure detection signal m from the switching control circuit failure detection circuit 12 and takes the logical sum to obtain the interface section failure detection signal o. It outputs to the interface unit and the switching circuit 13 adjacent to the other.

As described above, in the line switching control circuit of the present invention, one protection line is associated with an arbitrary number of working lines, and the working line in which a failure has occurred is switched to the protection line. Switching circuit 13 for inputting a reception signal from the side, switching circuit 14 for inputting a transmission signal from the device side, reception signal failure detection circuit 10 for detecting a failure of a reception signal from the line, and an interface section adjacent to one side. A switching control circuit 15 for inputting a failure interface section number and an interface section failure detection signal, outputting the failure interface section number to the interface section adjacent to the other, and outputting a switching control signal to the switching circuits 13 and 14, and this switching control circuit A switching control circuit failure detection circuit 12 for inputting a failure monitoring signal from 15; Enter the received signal failure detection signal from the signal signal failure detection circuit 10 receives the switching control circuit fault detection signal from the switching control circuit fault detection circuit 12,
An OR gate 16 that outputs an interface unit failure detection signal to the switching circuit 13 and the interface unit adjacent to the other, and an OR gate that inputs the received signals from the switching circuits 13 in the plurality of interface units corresponding to the lines and logically ORs them to the device side. It has 4 and 5.

When the interface section corresponds to the working line, the switching control circuit 15 outputs a switching control signal designating the working line to the switching circuits 13 and 14, and when there is a failure, the output of the switching circuit 13 is cut off.
When the interface unit corresponds to the protection line and the working system is in a normal state, the switching control circuit 15 turns off the outputs of the switching circuits 13 and 14, and the switching control circuit 1
When 5 detects a working line in which a failure has occurred based on the interface section failure detection signal and the failure interface section number, it outputs a switching control signal designating the working line in which the failure has been detected to the switching circuits 13 and 14. It is configured.

Next, the present invention is applied to two working lines and one protection line.
FIG. 1 shows a specific operation example when applied to the case of individual pieces.
And it demonstrates using FIG. First, the interface section 1 corresponds to the working line 6, the interface section 2 corresponds to the working line 7, and the interface section 3 corresponds to the protection line 8.
Is supported. When the working system is normal, the received signal a ₃ from the working line 6 is input to the switching circuit 13 via the receiving circuit 9 inside the interface section 1.
The switching control circuit 15 outputs a switching control signal h indicating that the corresponding line is the working line 6.
Output to 3 and 14. The switching circuit 13 uses the working line 6
The content of the received signal from is output to the OR gate 4 as the received signal a ₆ , and the received signal a ₁₃ is not output to any.
The switching circuit 14 outputs the transmission signal b ₁ as the transmission signal b ₉ to the transmission circuit 11 and does not input the transmission signal b ₂ from any of them. The transmission circuit 11 outputs the content of the transmission signal b _{9 to} the working line 6 as a transmission signal b ₃ .

By the same operation, the interface unit 2
Indicates the content of the received signal a ₄ from the working line 7 as the received signal a ₈
To the OR gate 5, and the received signal a ₇ is not output to any of them, but the content of the transmission signal b ₂ from the device side is output to the working line 7 as the transmission signal b ₄ . The interface unit 3 outputs a logical value 0 as a received signal a ₇ to the OR gate 4 by the switching circuits 14 and 13 and outputs a logical value 0 as a received signal a ₉ to the OR gate 5. Further, the reception circuit 9 in the interface unit 3 extracts the switching control communication reception signal i from the reception signal a ₅ from the protection line 8 and outputs it to the switching control circuit 15. Interface part 3
The switching control circuit 15 therein outputs the switching control communication transmission signal j to the transmission circuit 11, and this transmission circuit 11 inserts the switching control communication transmission signal j into the transmission signal b _{5 of the} protection line 8. As a result, the switching control circuit 15 in the interface unit 3 uses the protection line 8 to perform switching control communication with the opposite station, and exchanges fault line information and line switching request and permission.

Then, the OR gate 4 takes the logical sum of the received signal a ₆ and the received signal a ₇ and outputs the content of the received signal a _{3 on} the working line 6 to the device side as the received signal a ₁ . The OR gate 5 takes the logical sum of the received signal a ₈ and the received signal a ₉ and produces the received signal a ₂ as the received signal a ₂ on the working line 7.
Output the contents of ₄ to the device side. When a failure occurs in the reception signal a ₃ of the working line 6, the reception signal failure detection circuit 10 in the interface section 1 monitors the reception signal a ₃ of the working line 6 to detect the failure, The fault detection signal 1 is output. Further, when a failure occurs in the switching control circuit 15 in the interface unit 1, the switching control circuit failure detection circuit 1 which receives the failure monitoring signal k as an input.
2 detects the occurrence of a failure in the switching control circuit 15 and outputs a switching control circuit failure detection signal m. The logical sum of the reception signal fault detection signal 1 and the switching control circuit fault detection signal m by the OR gate 16 becomes the interface fault detection signal o, which is output to the switching circuit 13 and the interface unit 2.

When the switching circuit 13 recognizes the occurrence of a failure inside the interface section 1 by the interface section failure detection signal o, it outputs a logical value 0 as the received signal a ₆ . The interface section failure detection signal of the interface section 1 is input to the interface section 2 as the interface section failure detection signal c and is input to the switching control circuit 15 in the interface section 2. The switching control circuit 15 detects the occurrence of a failure in the interface section 1 by this signal, and outputs the failure interface section number d to the interface section 3 by indicating the number of the interface section 1. Switching control circuit 1 in the interface unit 3
When 5 detects the occurrence of a failure inside the interface section 1 by the failure interface section number d from the interface section 2 indicating the number of the interface section 1, a request for switching the working line 6 to the protection line is issued by the switching control communication transmission signal j. Send to the opposite station. The switching control communication reception signal i indicating the switching permission from the opposite station is received by the receiving circuit 9
And the switching control circuit 15 by extracting from the received signal a ₅ by
Input to the switching circuit 13, the switching control circuit 15 outputs the switching control signal h corresponding to the working line 6.
It outputs to 14.

The switching circuit 13 outputs the content of the received signal a ₅ from the protection line 8 to the received signal a ₇ , and the received signal a ₉
Outputs a logical value 0. Switching circuit 14 selects the transmission signal b ₁ of the transmission signal b ₁ and the transmission signal b _2, and outputs as a transmission signal b ₅ to the protection channel 8 through the transmitting circuit 11. As a result, the received signal a ₅ from the protection line 8
Is output to the device side as a reception signal a ₁ , and the contents of the transmission signal b ₁ sent from the device side becomes a transmission signal b ₅ to the protection line 8. By the above operation, the working line 6 is switched to the protection line.

When a failure occurs in the received signal a ₄ of the working line 7 or a failure occurs in the switching control circuit 15 inside the interface section 2, the switching control circuit 15 inside the interface section 3 causes the interface section 3 to operate. 2 is detected, the contents of the reception signal a ₅ from the protection line 8 is output to the device side as the reception signal a ₂ and the transmission signal b ₂
Is output as a transmission signal b ₅ to the protection line 8,
The working line 7 is switched to the protection line. When a failure occurs in the reception signal a ₅ of the protection line 8, the reception signal failure detection circuit 10 in the interface section 3 monitors the reception signal a ₅ to detect the failure and outputs the reception signal failure detection signal l. To do. Further, when a failure occurs in the switching control circuit 15 in the interface unit 3, the switching control circuit failure detection circuit 12 that monitors the failure monitoring signal k detects the failure occurrence in the switching control circuit 15, and the switching control circuit failure occurs. The detection signal m is output. The OR gate 16 takes the logical sum of the reception signal fault detection signal 1 and the switching control circuit fault detection signal m and outputs it as the interface fault detection signal o to the switching circuit 13. This switching circuit 1
3 outputs a logical value 0 to both the received signal a ₇ and the received signal a ₉ . As a result, the occurrence of a failure inside the interface unit 3 has no effect on the operation of the working line. Although the above description of the operation is an example in which the present invention is applied to the case of two working lines and one protection line, it can be similarly applied to the case of one protection line and an arbitrary working line.

[0021]

As described above, in the interface unit according to the present invention, the interface unit fault detection signal and the fault interface unit number are input from the interface unit adjacent to one side and the interface unit fault detection signal is input to the interface unit adjacent to the other side. When the interface unit corresponds to the working line, the interface unit that detects the fault is detected by inputting the interface unit fault detection signal and the fault interface unit number, and the interface unit adjacent to the other Failure interface section number indicating the interface section where the failure has occurred, and if the interface section corresponds to the protection line, the failure is detected by inputting the interface section failure detection signal and the failure interface section number. Since to detect the interface unit without, you can use the interface section of the same structure on the working and protection lines, and any n
There is an effect that a line switching of 1: n can be realized. Further, by eliminating the switching control unit other than the interface unit, there is an effect that the configuration can be simplified and the device can be made small.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a line switching control circuit according to the present invention.

FIG. 2 is a block diagram showing a configuration example of an interface unit in FIG.

FIG. 3 is a block diagram showing an example of a conventional line switching control circuit.

[Explanation of symbols]

 1 to 3 interface section 4,5 OR gate 6,7 working line 8 protection line 9 reception circuit 10 reception signal failure detection circuit 11 transmission circuit 12 switching control circuit failure detection circuit 13, 14 switching circuit 15 switching control circuit 16 OR gate

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[Procedure amendment]

[Submission date] June 1, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

A line switching control circuit according to the present invention includes a switching circuit for inputting a received signal from a line side, a switching circuit for inputting a transmission signal from a device side, and a failure of a received signal from the line. Received signal failure detection circuit to detect, and the failure interface section number and interface section failure detection signal are input from the interface section adjacent to one side, the failure interface section number is output to the interface section adjacent to the other side, and switching control to both switching circuits is performed. A switching control circuit for outputting a signal, a switching control circuit fault detection circuit for inputting a fault monitoring signal from the switching control circuit, and a switching control circuit fault detection circuit for inputting a received signal fault detection signal from the received signal fault detection circuit Input the switching control circuit failure detection signal from the And OR gate which outputs to the interface portion adjacent to the circuit and the other switches the detection signal, and a gate to be output to the device side ORs enter the received signal from the switching circuit in a plurality of interface units to the line interface. A first interface (1) connected between the first working line (6) and the first device, and a first interface (1) connected between the second working line (7) and the second device. It is composed of two interfaces (2) and a third interface (3) connected to the protection line (8), where each interface is the first to the device.
The second output end and the first and second input ends have the same configuration, and the first interface of the first interface is provided.
Of the first interface of the second interface and the signal from the first output of the third interface via the first OR gate (4) becomes the reception signal (a ₁ ) to the first device. The signal from the end and the second output end of the third interface becomes a reception signal (a ₂ ) to the second device via the second OR gate (5) and a transmission signal (b ₁ ) from the first device. ) Is input to the first input end of the first interface and the first input end of the third interface, and
A transmission signal (b ₂ ) from the device of ( ₁ ) is a line switching control circuit configured to be input to a first input terminal of a second interface and a second input terminal of a third interface. (1, 2, 3), first enter the received signal from the line _{(a 11),} an output from the second output terminal _{(a 12, a 13)} a first switching circuit (1 3) to , The transmission signal (b ₁ , b ₂ ) from the device
1, transmission signal to the line input to the second input terminal (b ₉ )
And a second switching circuit (14)
And the signal state at the input and output ends of the second switching circuit
With control means (10, 12, 15, 16) for controlling
The control means has its interface connected to the working line.
If it is connected and is normal, the second output terminal is output.
With no force, and the second input end with no input.
Is connected to the protection line and is
Output is normal, the first and second outputs are output
No input and no input at the first and second input terminals
And that interface is not connected to the working line.
If there is an error, the first output end will also not output
And the first input end is also set to no input
Interface is connected to the protection line and the current
If it is always the first one that corresponds to the abnormal interface.
If either the 1st or 2nd output end is set to have output
First or second corresponding to the abnormal interface
Controls that one of the input terminals of
is there.

Claims (1)

[Claims] 1. A first switching for inputting a received signal from a line side in a line switching control circuit for switching one working line to an arbitrary number of working lines and switching a working line in which a failure has occurred to a working line. A circuit, a second switching circuit for inputting a transmission signal from the device side, a reception signal failure detection circuit for detecting a failure of a reception signal from the line, and an interface section number and an interface section failure from an interface section adjacent to one side A switching control circuit that inputs a detection signal, outputs a failure interface section number to the interface section adjacent to the other, and outputs a switching control signal to the first and second switching circuits, and a failure monitoring signal from the switching control circuit. A switching control circuit for inputting a fault detection circuit, and a received signal fault detection signal from the received signal fault detection circuit. A switching control circuit fault detection signal from the switching control circuit fault detection circuit, and outputs an interface unit fault detection signal to the first switching circuit and the interface unit adjacent to the other. A second and a third OR gate for receiving the received signals from the first switching circuits in the plurality of interface units corresponding to the lines and taking a logical sum and outputting to the device side, when the interface unit corresponds to the working line , The switching control circuit outputs a switching control signal designating a working line to the first and second switching circuits, and when a failure occurs, the output of the first switching circuit is cut off, and the interface unit corresponds to the protection line. When the working system is in a normal state, the switching control circuit operates as a switch between the first and second switching circuits. When the switching control circuit detects a working line in which a failure has occurred according to the interface section failure detection signal and the failure interface section number, the switching control signal for designating the working line in which the failure is detected First and second
The line switching control circuit is characterized by outputting to the switching circuit.