JPH08307975A - Line interface circuit - Google Patents

Abstract

PURPOSE: To prevent the deterioration of communication quality accompanied by switching systems and to improve the reliability of the whole communication equipment as a result concerning the line interface circuit of redundant constitu tion provided with in-use and spare signal processing systems. CONSTITUTION: The line interface circuit 100 provided with the in-use and spare signal processing systems is provided with a framer 112 connected to a line and provided with a function assembling and disassembling a transmission and reception frame and detecting the state of the line and a system switching part 113 connecting and switching the framer 112 to the in-use or spare signal processing system. Thus, the framer 112 supplies a line state signal for both signal processing systems so that an external monitoring device monitors the state of the line through both signal processing system to send a system switching signal to the system switching part, as required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redundant line interface circuit having active and standby signal processing systems.

With the recent diversification and sophistication of communication equipment,
Communication networks are also required to have high density and high reliability. For example, ISDN (Integrated Services Digital Network) provides PRI (Primary Rate Interface) as an interface for integrating and multiplexing various communication lines, but in PRI, a line control unit fails. Then, all the multiplexed lines are cut off. In order to avoid this, it is necessary to have a redundant configuration in which the working system and the standby system are provided in the line control unit, but in order to further improve reliability, when a line error occurs, quickly and minimize the error. It is required to switch to the standby system and restore the line.

[0003]

2. Description of the Related Art FIG. 13 shows an example of the configuration of a line accommodation section in a conventional electronic exchange. The line is connected to a line interface circuit, and the line interface circuit is connected to a line control unit that is duplicated in a working system (0 system) and a standby system (1 system). The line interface circuit is composed of a framer (or a format unit), a framer control unit (or a format control unit), and a system switching unit. The framer and the framer control unit are provided for the line control units of both systems. The framer assembles / disassembles the transmission / reception frame, and the framer control unit sends framer control data (or line control signal) based on the control information given from the line control unit to the framer. The system switching unit switches between the 0 system and the 1 system according to the system switching signal sent from the system monitoring control unit.

FIG. 14 shows an example of a mounting structure in a conventional electronic exchange. The main control unit that controls the entire system and the line control unit that controls the line are installed on different racks, and the system control unit is installed in the main control unit, and the line control unit has multiple communication units. Is installed. Each communication unit accommodates a plurality of lines. Line data is transmitted and received between the main control unit and each communication unit through the bus a. Inside each communication unit, the line controller is duplicated into the 0 system and the 1 system, the 0 system is used in a normal state, and the system is switched to the 1 system when an abnormality occurs in the 0 system. The system monitoring controller in the main controller is
Monitoring is performed based on the line data received from each communication unit, and a system switching instruction is directly sent to the communication unit in which an abnormality has been detected through the cable b.

FIG. 15 shows a configuration example of the above communication unit. A line control unit and a line interface unit are provided for each line accommodated in the communication unit. The line control unit uses the line interface type (PRI,
The line interface circuit corresponds to the line interface type although it is common regardless of BRI). The line control unit is duplicated in the 0 system and the 1 system, and the system switching is performed inside the line interface circuit. Further, the line management processor unit for managing the inside of the communication unit is also duplicated in the 0 system and the 1 system.

[0006]

The line interface of the conventional electronic exchange or the like has the following problems regarding the system switching of the redundant configuration.

Delay in response when a failure occurs in the line itself As shown in FIG. 13, in the conventional line interface unit, since the system switching is performed on the line side rather than the framer, when the line itself is abnormal , The line failure was detected by once switching from the 0 system to the 1 system and confirming that the line still did not recover. Therefore, there is a problem that the response at the time of line failure becomes slow.

Effect of Chattering at System Switching by Relay Since the voltage level of the signal input / output to / from the system switching unit provided on the line side is different from the logic level such as TTL, the system switching unit may be composed of semiconductor parts. I couldn't do it, and it consisted of relays. Therefore, the chattering accompanying the switching operation of the relay causes a line data error on the local station side and a line interruption error on the opposite side.

Partial loss of line data during system switching Since the system switching signal occurs asynchronously with the frame of the line signal, system switching occurred in the middle of the frame and some data was lost.

Problem of Compatibility with Line Interface Specifications When the line control unit and the line interface unit are separated into different cards, only the line interface unit needs to be replaced to change the line interface specifications. . Conventionally, as shown in FIG. 16, a control register is provided on the side of the line control unit, and the line interface unit accesses the control register through a processor bus of the line control unit, so that the line control unit and the line interface unit are connected. The control information was passed in. However, due to factors such as customer-requested specifications (number of lines, number of multiplexed redundant configurations, fault detection specifications, etc.), recommendation types (recommendations such as CCITT, TTC, etc.) and specification changes due to an increase in the version number of the recommendations, the line interface specifications are There are various types, and the scale of the control register required varies depending on the specifications. Therefore, in order for the line control unit to support various line interface specifications, it was necessary to mount the maximum scale register.

Sending an indefinite signal to the line at startup Since there are only two 0-system terminals and 1-system terminals on the switching side of the system switching unit, the line must be either 0-system or 1-system immediately after the device is powered on. Will be connected to one or the other. Therefore, for example, if the line control unit is not in the normal operation state, an abnormal signal may be sent to the line.

Problem of testability of line interface The line interface unit was only switched by a system switching instruction sent from an external device. Therefore, even when the line interface unit is tested independently, it is necessary to prepare an external device that issues a system switching instruction, and system switching during the test cannot be easily performed.

Complicated wiring for system switching instruction As shown in FIGS. 14 and 15, a main controller equipped with a system monitoring control unit for determining system switching and a line interface unit for system switching are provided. If the installed line controller is on a different rack, in addition to the bus that sends and receives communication data between the main controller and the line controller, a cable for the system monitoring controller to send a system switching instruction to the line interface is required. become. Therefore, when the main control unit controls multiple line control units, a cable for communication data and a cable for system switching signals must be connected to each line control unit. It was complicated.

The present invention has been made in view of the above problems, and an object thereof is to prevent deterioration of communication quality due to system switching in a line interface circuit having a redundant configuration, and to improve reliability of the entire communication device. To do.

[0015]

FIG. 1 is an explanatory view of the principle according to the present invention. However, although the configuration of the line interface circuit in which the signal processing system is duplicated is shown in FIG. 1 for simplification, the present invention can be applied regardless of the number of multiplexing of the signal processing system.

In order to solve the above problems, a line interface circuit 100 according to the present invention is connected to a line 103, and has a framer 112 having a function of assembling / disassembling a transmission / reception frame and detecting a line state. A system switching unit 113 for switching connection of the framer 112 to the current signal processing system 110 or the spare signal processing system 111 is provided, and the line state signal detected by the framer 112 is supplied to both signal processing systems. Characterize.

The framer 11 connected to the line 103
2 decomposes the received frame and sends the extracted data to the signal processing system, and assembles the transmission frame from the data received from the signal processing system. Also, framer 1
A line 12 detects the state of the line 103 and supplies a line state signal to the working and protection signal processing systems, respectively. In the normal state, the system switching unit 113 sets the framer to the active signal processing system 110.
Connected to

At this time, when a monitoring unit (not shown) detects a line abnormality, the line state signal is read from the spare signal processing system 111 via the spare line control unit 102 to check the line state. As a result of this inspection, if the line state is normal, the monitoring unit determines that the line control unit 10 is in use.
1 or it is judged that a failure has occurred in the signal processing system 110, and a system switching signal for instructing switching to the standby system is sent to the line interface circuit 100. Also, if there is an abnormality in the line status, it is judged that a failure has occurred in the line itself,
Take a prescribed failure response without sending a system switching signal. As a result, when a failure occurs in the line itself, the failure can be promptly dealt with without wasteful system switching.

The line interface circuit 1 of the present invention
In the configuration of 00, since the system switching unit 113 is not directly connected to the line 103, the voltage level of the signal input / output to / from the system switching unit 113 from the line side can be the logical level of the IC in the circuit. Therefore, since the system switching unit 113 can be composed of a semiconductor component such as TTL, the problem of chattering that occurs when the system switching unit is composed of a relay is eliminated.

Further, in the line interface circuit 100 according to the present invention, the framer 112 generates a timing signal indicating the timing of the frame boundary, and based on the timing signal from the framer 112, it is sent from the outside as a switching instruction to the system switching unit 113. System switching signal
The system can be configured to further include a system switching control unit 114 that adjusts the phase so that the system switching timing becomes a frame boundary timing and sends the phase switching timing to the system switching unit 113.

A system switching signal from the outside, which is sent from the system monitoring device or the like, is input to the system switching control unit 114 of the line interface circuit 100. On the other hand, the framer 112 supplies a timing signal indicating the timing of the frame boundary of the transmission / reception frame to the system switching control unit 114. Based on this timing signal, the system switching control unit 114 performs phase adjustment so that the system switching timing of the system switching signal matches the timing of the frame boundary, and then the system switching unit 11
Send to 3. As a result, no matter what timing the system switching signal is generated, the system switching is performed between frames, so that some communication data will not be lost during system switching.

Further, the line interface circuit 100 according to the present invention holds a control register 115 for holding control information (information different according to customer's request specifications) to be transferred between the line control units 101 and 102 located outside. , 116 may be further provided.

The signal processing systems 110 and 111 of the line interface circuit 100 are control registers 115 and 11 provided on the line interface circuit side, not on the line control section side.
Control information is transferred between the line control units 101 and 102 via the communication control unit 6.

Further, the line interface circuit 100 according to the present invention is provided with an idle signal generating section 117 for outputting an idle signal inside or outside the circuit so that the output from the signal processing system becomes normal after the power of the device is turned on. Until then, the system switching unit 113 may connect the framer 112 to the idle signal generating unit 117.

The system switching unit 113 has a neutral contact in addition to the contacts for switching the signal processing system, and the neutral contact generates the predetermined idle signal.
Connected to 17. System switching unit 11 when the device is powered on
In the initial state, the framer 112 connects the framer 112 to the idle signal generator 117, and after the line controller etc. starts up and the output from the signal processing system becomes normal, the framer 11 is started.
2 is connected to the signal processing system. As a result, the line interface circuit 100 does not send an indefinite signal to the line 103 until the power is turned on to the stable state.

Further, the line interface circuit 100 according to the present invention can be constructed so that the system switching unit 113 can switch the system by manual operation.

With this configuration, when the line interface circuit 100 is tested independently, system switching can be performed manually without separately preparing a device for transmitting a system switching signal.

Further, in the present invention, transmission of communication data passed between the control device and the communication device is carried out for a device configuration in which an external control device transmits a system switching signal to a communication device having a redundant configuration. A system switching signal transmission method in which a system switching signal is transmitted from the control device to the communication device through the path can be used.

For example, in the electronic exchanges shown in the conventional examples of FIGS. 14 and 15, the line controller equipped with the line interface circuit is different from the main controller equipped with the system monitoring controller for sending the system switching signal. It has a structure in which a bus a for transmitting and receiving communication data between the main control device and the line monitoring device and a cable b for transmitting a system switching signal to each line interface circuit by the system monitoring control unit are separately provided on the rack. ing. In this case, if the system switching signal transmitting method of the present invention is applied so that the system switching signal sent from the system monitoring control unit is also transmitted to each line interface circuit through the bus a, the cable b becomes unnecessary, and the inter-device Wiring is simplified.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a configuration example of a PRI line accommodation unit of an electronic exchange equipped with a line interface circuit as an embodiment of the present invention. In the figure, 1 is a line management processor unit, 2 and 3 are line control units of 0 system and 1 system, respectively, and 4 and 5.
Are framer control units of 0 system and 1 system, 6 and 7 are selectors, 8 is a framer, 9 is a transmitting unit, and 10 is a receiving unit. The line interface circuit is composed of framer control sections 4 and 5, selectors 6 and 7, framer 8, transmitting section 9 and receiving section 10.

The line management processor unit 1 manages the line control units of both systems and outputs a system switching signal as needed. The selectors 6 and 7 are semiconductor switches that switch between the 0 system and the 1 system in response to the system switching signal from the line management processor unit 1. The selector 6 connects one of the frame control unit 4 or the frame control unit 5 to the framer 8. The selector 7 connects one of the line control unit 2 and the line control unit 3 to the framer 8. The system switching signal may be output by the line management processor unit 1 by itself, or may be output by the line management processor 1 in response to a system switching instruction from an external control device.

For example, when the 0 system is selected, the frame controller 4 supplies the framer control data based on the control information received from the line controller 2 to the framer 8 via the selector 6. The framer 8 assembles / disassembles the frames transmitted / received by the transmitter 9 and the receiver 10 according to the framer control signal. Downlink line data is sent from the framer 8 through the selector 7 to the line controller 2.
Uplink line data is sent from the line controller 2 through the selector 7 to the framer 8. Further, the framer 8 detects the line state and supplies the line state signal to both the frame control units 4 and 5 regardless of the currently selected system.

Now, in this state, the line control unit 2 of system 0
When the line abnormality is detected at, the line management processor unit 1 checks the line state through the line control unit 3 of the 1st system.
That is, the line management processor unit 1 reads the line state signal from the framer control unit 5 via the line control unit 3. When the line status is normal, the line management processor unit 1 sends a system switching signal to the selectors 6 and 7, thereby
The system is switched from the system to the 1 system. If the line status is abnormal, the line management processor unit 1 determines that the line itself is in failure, and does not switch the system, and notifies the host monitoring device of the line failure.

With this configuration, when a line abnormality is detected, it can be specified whether the line control unit or the like is faulty, or the line itself is faulty, and the fault can be swiftly performed without wasteful system switching. Can handle.

Further, by disposing the framer 8 on the line side of the system switching section (selectors 6, 7), the voltage level of the line data and control signal can be handled as the logic level of the IC, so that the selector is an IC such as TTL. Can be configured logically. As a result, problems such as the line data error at the local station and the instantaneous line disconnection error at the opposite station, which the conventional system switching unit composed of the relay has, are solved, and the data at the time of system switching is guaranteed. Further, since one framer can be shared by the 0-system and the 1-system, the hardware scale of the circuit can be reduced.

FIG. 3 shows an embodiment in which a system switching control unit 11 for adjusting system switching timing is added to the configuration of FIG. In this embodiment, the framer 8 outputs a timing signal indicating the frame timing of the signal transmitted / received from the line. The system switching control unit 11 phase-adjusts the system switching signal from the line management processor unit 1 based on the timing signal from the frame 8, and sends the phase-adjusted system switching signal to the selectors 6 and 7.

Adjustment of system switching timing by the system switching control unit 11 will be described with reference to the timing chart of FIG. In the figure, a is a timing signal output from the framer 8, b is a system switching signal output from the line management processor unit 1, c is a system switching signal after phase adjustment, and d is a line signal. The system switching control unit 11 constantly monitors the timing signal from the frame. On the other hand, when it becomes necessary to switch the system, the line management processor unit 1 sends a system switching signal asynchronously to the timing of the frame.
Output to 1. The timing signal a is a signal indicating the frame head of the line signal d by a pulse. For example, the system switching signal b sent from the line management processor unit 1 is 0
Even if the "H" changes to "L" to switch from the 1st system to the 1st system and the "L" to "H" changes to switch from the 1st system to the 0th system, the system switching control unit 11 is
The system switching signal c, which is phase-delayed with the change in 1 and the change in 2, is input to the selectors 6 and 7, respectively. As a result, the system switching always occurs between the frames of the line signal d.

With this configuration, line data errors due to system switching can be prevented, and the line management processor unit 1 or an external monitoring device can perform system switching at any time without affecting the line data. .

FIG. 5 shows a path of control information transferred between the line control unit and the line interface unit. The processor of the line control unit controls the line interface circuit via the register. This register is provided inside the line interface circuit as a register # 0 for the line control unit 2 of system 0 and a register # 1 for the line control unit 3 of system 1. Since the register # 0 is connected to the processor bus of the processor # 0 of the line control unit 3 and the register # 1 is connected to the processor bus of the processor # 1 of the line control unit 4, the processor of each line control unit corresponds to the corresponding register. Can be accessed directly.

Next, the control of the line interface circuit by the line controller will be described with reference to FIG. In addition to the above registers # 0 and # 1, the line interface circuit includes a register 41 in the framer control unit 4, a register 51 in the framer control unit 5, and a register 81 in the framer 8.
Is provided. The line control units 2 and 3 control the line interface circuit via these five registers. The framer 8 holds the detected line status data in the internal register 81. This line state data is transmitted to the line control unit via the framer control unit as a line state signal. The framer control information sent from the line control unit 2 and the line control unit 3 is held in the register 41 in the framer control unit 4 and the register 51 in the framer control unit 5, respectively, and each framer control unit receives the framer 8 through the selector 6.
The framer control signal is sent to.

Registers # 0 and # 1 are registers for holding control information other than the above, and are used for detection and transmission of fault information, etc., and are required by customer (specification of number of lines, number of redundant configuration multiplexing, fault detection specification). Etc.) is provided according to the size. If the same line control unit supports various types of line interfaces (PRI, BRI, X.21, V.35, etc.), it is possible to change the interface by replacing the card of the line interface circuit. The required size of registers # 0 and # 1 also differs depending on the type of interface.

Therefore, registers # 0 and # 1 having a size according to the type of the line interface and the customer's specifications are provided in the line interface circuit, and the line controller, which is a common card, can read / write these registers. By designing like this, like the conventional technology, the maximum scale register that can support various types of line interfaces is provided in the line control unit, or the register in the line control unit is expanded when the specifications of the line interface are changed. Since it is not necessary, the hardware scale of the device can be reduced,
It is possible to flexibly respond to changes in specifications.

FIG. 7 is a diagram showing the connection of each terminal of the selector 7 in the above embodiment. In this case, since there are only two 0-system terminals and 1-system terminals on the switching side, the line is always connected to either one of the line control units via the framer 8. However, after the power of the electronic exchange is turned on, it takes some time for the line control unit to reach the normal operating state, and the output of the line control unit may become unstable during that time, so an abnormal signal is sent to the line. There is a possibility.

This problem can be solved by further providing the selector 7 with a neutral terminal N. FIG. 8 is a diagram showing the connection of each terminal of the selector 7 having such a configuration. The terminal N of the selector 7 is connected to the idle signal generator 12. The idle signal generator 12 fixedly outputs, for example, a signal of “1” to the terminal N of the selector 7. When the power of the electronic exchange is turned on, the selector 7 is always connected to the idle signal generator 12, and after the line controller is in a normal operating state, the line 0 or 1 line is transmitted according to the line switching signal of the line management processor 11. Connect to the control unit. Therefore, in the initial state of the selector 7, since the signal of "1" is fixedly input to the framer 8, an abnormal signal is not transmitted to the line.

In the case of a line using HDLC (high level data link control procedure), if the idle signal generator 12 outputs a flag ('7E'H), the flag is output from the line when the power is turned on. Since the pattern is transmitted, it is possible to synchronize the flag with the terminal, modem or the like to which the line is connected.

FIG. 9 shows an embodiment in which both the selectors 6 and 7 of the line interface section have a neutral terminal N and the idle signal generating section 12 is connected to the terminal N.
The idle signal generator 12 may be provided inside or outside the line interface circuit.

FIG. 10 shows a selector 6 in the case where the line interface circuit system can be switched manually.
A configuration example of the peripheral portion of (or 7) is shown. The manual switch section 13 can generate a system switching signal by manual operation. The selector 14 includes a system switching signal from the line management processor unit 1 and the manual switch unit 1.
One of the system switching signals from 3 is selected and input to the selector 6 (or 7). Which system switching signal the selector 14 selects can be set manually. Therefore, the selector 14 is set so that the system switching signal from the line management processor unit 1 is selected during normal operation, and the system switching signal from the manual switch unit 13 is selected by the selector 14 when testing the line interface circuit. If set to, the system can be easily switched by a tester's manual operation, so that it is not necessary to prepare the line management processor unit 1 even when the line interface circuit is individually tested.

FIG. 11 shows a system switching signal sent from the main control unit to each line interface circuit in the line control unit in the configuration of the electronic exchange shown in the conventional example of FIGS. This is an embodiment in which transmission is performed through a bus a for transmitting and receiving line data between control devices. In this embodiment, the main control unit judges system switching based on the line data sent from the line control unit and issues a system switching command, and the line management processor unit in the line control unit switches the system via the bus a. System switching is performed by receiving an instruction and sending a system switching signal to the line interface circuit.

FIG. 12 shows an image of data on the bus a in the case of the conventional example and in the case of the present embodiment. In the present embodiment, the system a is commonly used for the line data and the system switching instruction by inserting the system switching instruction between the line data on the bus a.

With this configuration, the cable conventionally used for transmitting the system switching signal from the main control device to each line interface circuit in the line control device becomes unnecessary.

[0051]

As described above, according to the present invention, when a line abnormality is detected, it is possible to easily identify the fault of the line itself or the fault of the signal processing system and make a fault. It can respond quickly. Furthermore, it is possible to avoid an error or partial loss of the line data at the time of system switching, occurrence of a momentary line disconnection error on the opposite side, and transmission of undefined data to the line at power-on. Therefore, it greatly contributes to the improvement of the performance and reliability of the device.

Further, according to the present invention, it is possible to reduce the hardware scale of the communication device equipped with the line interface circuit, reduce the number of cables, simplify the wiring, etc., and to flexibly change the specifications of the line interface. It is possible to deal with it

Further, according to the present invention, the line interface circuit can be easily tested, which contributes to the improvement of the quality of the device.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram for explaining an example of the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a timing chart for explaining timing adjustment of system switching by the system switching control unit.

FIG. 5 is a diagram showing an example of a transfer path of control information between a line control unit and a line interface circuit.

FIG. 6 is a diagram for explaining control of a line interface circuit by a line control unit.

FIG. 7 is a configuration example of a peripheral portion connected to the system switching unit.

FIG. 8 is a configuration example of a peripheral part connected to a system switching part having a neutral terminal.

FIG. 9 is a configuration example of a line accommodating unit when a neutral terminal is provided in the system switching unit.

FIG. 10 is a configuration example of a system switching unit and its peripheral portion that enable system switching by manual operation.

FIG. 11 is a configuration example of an electronic exchange to which the system switching signal transmission method of the present invention is applied.

FIG. 12 is a diagram showing an image of transmission data according to the system switching signal transmission method of the present invention.

FIG. 13 is a configuration example of a line accommodation unit in a conventional electronic exchange.

FIG. 14 is a mounting configuration example of a conventional electronic exchange.

FIG. 15 is an example of a system switching signal transmission method in a conventional electronic exchange.

FIG. 16 is a diagram showing an example of a transfer path of control information between a conventional line control unit and a line interface unit.

[Explanation of symbols]

 1 line management processor unit 2 line control unit (0 system) 3 line control unit (1 system) 4 format control unit (0 system) 5 format control unit (1 system) 6, 7 selector 8 framer 9 transmission unit 10 reception unit 11 System switching control unit 12 Idle signal generation unit 13 Manual switch unit 14 Selectors 41, 51, 81 Registers 100 Line interface circuit 101 Line control unit (active system) 102 Line control unit (standby system) 103 Line 110 Signal processing system (active system) ) 111 signal processing system (standby system) 112 framer 113 system switching unit 114 system switching control unit 115, 116 control register 117 idle signal generation unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Sugimoto 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Kansai Communication Systems Co., Ltd. Communication system Co., Ltd.

Claims (7)

[Claims] 1. A redundant line interface circuit having an active and a standby signal processing system, the framer being connected to a line for assembling / disassembling a transmission / reception frame and detecting a line state. A line interface circuit comprising a system switching unit for connecting and switching the framer to an active or standby signal processing system, and configured to supply a line status signal detected by the framer to both signal processing systems. 2. The line interface circuit according to claim 1, wherein the system switching unit is composed of a semiconductor component. 3. The framer generates a timing signal indicating the timing of a frame boundary, and based on the timing signal from the framer, a system switching signal sent from the outside as a switching instruction to the system switching unit is used as a system switching timing. 3. The line interface circuit according to claim 1, further comprising a system switching control unit that adjusts the phase so that it becomes a timing of a frame boundary and sends it to the system switching unit. 4. The line interface circuit according to claim 1, further comprising a control register for holding line control information transferred to and from an external line control device. 5. An idle signal generator for outputting an idle signal is provided inside or outside the line interface circuit, and the system switching unit is provided until the output from the signal processing system becomes normal after the power is turned on. The line interface circuit according to any one of claims 1 to 4, wherein the framer is connected to the idle signal generator. 6. The line interface circuit according to claim 1, wherein the system switching unit is configured to switch the system by manual operation. 7. A system switching signal transmission method in which an external control device transmits a system switching signal to a communication device having a redundant configuration, the transmission path of communication data being passed between the control device and the communication device. A system switching signal transmission method in which a system switching signal is transmitted from the control device to the communication device via the communication system.