JP2000295255A - Redundant conversion method of transmission line and system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restore a transmission line without the down of a whole system by connecting a communication station to one of a plurality of transmission lines with change-over equipment, time-sequentially transmitting a fixed signal and changing-over the transmission line into the one in another system by means of change-over equipment when the reception of the fixed signal is stopped. SOLUTION: LAN is constituted of a monitoring and controlling station 3 as a host and a plurality of input/output terminals 4. Each one of the transmission lines 1 and 2 and a branch transmission lines 10 and 20 is adopted as a normal system, the other is adopted as a stand-by system and each one of them is used in transmission line change-over equipment 5. The monitoring and controlling station 3 and the input/ output terminals 4 repeatedly transmit a transmission line recognizing signal with the data body part of a MAC frame as a free pad by fixed period to the normal system transmission lines 1 and 2 under usage at present with a destination address as a broadcast. The input/output terminals 4 at a reception side identify the transmission line recognizing signal by the free data body part and the transmission lines 1 and 2 during usage at present are judged to have fault unless an input exists after the time of the fixed period elapses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a bus-type LAN having a plurality of transmission lines and, when a failure occurs in any of the transmission lines, switching to a normal transmission line. The present invention relates to a transmission line redundancy method and a system using the method.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram showing a configuration of a conventional bus type LAN. In FIG. 13, 1 is a bus type L
A plurality of branch transmission lines 10, 10,... Branching from each node of the trunk transmission line 1 are provided. Also, one of the branch transmission lines 10, 10,.
A monitoring control station 3 having N host functions is connected, and input / output terminals 4, 4 as terminal devices are connected to the other two branch transmission lines 10, 10, respectively.

The conventional bus-type LAN is configured as described above, and performs data transmission between the supervisory control station 3 and the input / output terminals 4 and 4 by using the main transmission line 1 and the branch transmission lines 10 and 10.
Via.

[0004] When a failure occurs in any transmission path of such a bus type LAN, the function of the entire LAN stops. For this reason, for example, the monitoring control station 3 can confirm that a failure has occurred due to the system going down, but it is impossible to specify the failure location and recover the failure. In particular, when a physical failure such as a transmission line disconnection occurs, a worker is dispatched to visually inspect the transmission line disconnection point, or to check the branch transmission lines 10, 10,. After the fault location is identified by exchanging the transmission path in the order of the path 1, the transmission path is repaired or replaced.

[0005]

However, since it takes a great deal of time and labor to specify a failure location which is a prerequisite for recovery work, there is a problem that the LAN cannot be used until the recovery. Becomes more difficult as the size of the LAN increases.

In Japanese Patent Application Laid-Open No. 6-62017, all transmission lines are divided into two systems, one is a regular transmission line, and the other is a standby transmission line. For example, a bit error occurring in LAN communication is monitored. When the number of errors reaches a predetermined number of times, it is determined that a failure has occurred in the service transmission line, and a method of making the transmission line redundant from the service transmission line to the standby transmission line is disclosed. According to the method, there is an advantage that the work of restoring the service transmission line can be performed after switching to the standby transmission line.

The present invention has been made in view of the above circumstances, and each communication station transmits an acknowledgment signal at a predetermined time period and receives the acknowledgment signal instead of monitoring a bit error in normal data transmission. When each communication station has stopped receiving the confirmation signal for a predetermined time or more, it is determined that a failure has occurred in the transmission path of the currently used system, and by switching to a transmission path of another system, Transmission line redundancy method and method capable of performing fault location and recovery while using a normal transmission line even when a failure occurs in the transmission line of the system It is an object of the present invention to provide a system using a computer.

[0008]

According to a first aspect of the present invention, there is provided a method for making a transmission line redundant, wherein a communication station connected to any one of a plurality of transmission lines via a switch transmits a predetermined signal. While transmitting serially and receiving the predetermined signal from another communication station, if the reception of the predetermined signal is interrupted for a predetermined time, a switching instruction is output to the switch, and the switch is The transmission path of the connected system is switched to the transmission path of another system based on the instruction.

In the transmission line redundancy method according to the second invention, a communication station is connected to any one of a plurality of transmission lines via a switch, and each switch transmits a predetermined signal in time series. To receive the predetermined signal from another switch, and when the reception of the predetermined signal is interrupted for a predetermined time, switch the transmission path of the connected system to the transmission path of another system. Features.

A third aspect of the present invention is a transmission line redundancy method according to the first or second aspect, wherein information indicating a switching state of a transmission line is added to the predetermined signal, and The information is displayed on display means connected to the transmission line via the switch.

According to a fourth aspect of the present invention, there is provided a transmission line redundancy method, wherein a first communication station connected to a plurality of transmission lines transmits a predetermined signal in a time-series manner, and any one of the plurality of transmission lines. When the second communication station connected to the one via the switch receives the predetermined signal and the reception of the predetermined signal is interrupted for a predetermined time, the second communication station outputs a switching instruction to the switch, and The switching unit switches the transmission path of the connected system to the transmission path of another system based on the switching instruction.

According to a fifth aspect of the present invention, there is provided a transmission line redundancy method, wherein a first communication station connected to a plurality of transmission lines transmits a predetermined signal in a time-series manner, and any one of the plurality of transmission lines. A second communication station is connected to one of them via a switch, and when the switch receives the predetermined signal and the reception of the predetermined signal is interrupted for a predetermined time, the transmission path of the connected system Is switched to a transmission line of another system.

According to a sixth aspect of the present invention, there is provided the transmission line redundancy method according to the fourth or fifth aspect of the present invention, wherein the switching device transmits information relating to a transmission line of a system in which the predetermined signal is received. Displaying the information on display means connected to the plurality of transmission lines via the switch.

[0014] A transmission line redundancy method according to a seventh aspect of the present invention is characterized in that a communication station connected to a plurality of transmission lines transmits the same information via the plurality of transmission lines.

According to an eighth aspect of the present invention, there is provided a transmission line redundancy system comprising: a plurality of transmission lines; a plurality of switches selectively connected to any one of the plurality of transmission lines; A communication station that performs communication via the communication unit, wherein each communication station transmits a predetermined signal in a time-series manner; a reception unit that receives the predetermined signal from another communication station; Output means for outputting a switching instruction to the switch when reception of the predetermined signal is interrupted for a predetermined time, wherein each of the switches switches a transmission path of a connected system to another based on the switching instruction. It is characterized by being switched to a system transmission line.

According to a ninth aspect of the present invention, there is provided a transmission line redundancy system comprising: a plurality of transmission lines; a plurality of switches selectively connected to any one of the plurality of transmission lines; A communication station for performing communication via the switching unit, wherein each switching unit includes a transmitting unit for transmitting a predetermined signal in time series, and a receiving unit for receiving the predetermined signal from another switching unit; When the reception of the predetermined signal is interrupted for a predetermined time,
The transmission line of the connected system is switched to the transmission line of another system.

A transmission line redundancy system according to a tenth aspect of the present invention is the transmission line redundancy system according to the eighth or ninth aspect, wherein: an adding means for adding information indicating a switching state of the transmission line to the predetermined signal; A display unit connected to the communication line for displaying the information.

[0018] A transmission line redundancy system according to an eleventh aspect of the present invention comprises: a plurality of transmission lines; a first communication station connected to the plurality of transmission lines and transmitting a predetermined signal in time series; A switch for selectively connecting to any one of the transmission lines of the system, and a second communication station for performing communication via the switch, wherein the second communication station receives the predetermined signal. Means, and output means for outputting a switching instruction to the switch when the reception of the predetermined signal by the receiving means is interrupted for a predetermined time, wherein the switch is based on the switching instruction.
The transmission line of the connected system is switched to the transmission line of another system.

According to a twelfth aspect of the present invention, there is provided a transmission line redundancy system comprising: a plurality of transmission lines; a first communication station connected to the plurality of transmission lines and transmitting a predetermined signal in time series; A switching unit selectively connected to any one of the transmission lines of the system, and a second communication station communicating through the switching unit, wherein the switching unit receives the predetermined signal. Wherein when the reception of the predetermined signal by the receiving means is interrupted for a predetermined time, the transmission path of the connected system is switched to the transmission path of another system.

A transmission line redundancy system according to a thirteenth aspect is the transmission line redundancy system according to the eleventh or twelfth aspect, wherein the transmission line redundancy system is connected to the plurality of transmission lines via the switch. Is further provided with display means for displaying information related to the transmission path of the system that has received the predetermined signal.

According to a fourteenth aspect of the present invention, a transmission line redundancy system includes a plurality of transmission lines and a plurality of communication stations connected to the plurality of transmission lines. It is characterized in that the same information is transmitted via a road.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments.

Embodiment 1 FIG. 1 shows a bus type LAN as a system using the transmission line redundancy method according to the present invention.
FIG. 3 is a block diagram showing Embodiment 1 of the present invention. In FIG. 1, reference numerals 1 and 2 denote trunk line transmission lines of a bus-type LAN having two systems. Each of the trunk line transmission lines 1 and 2 is provided with a plurality of branch line transmission lines 10 and 20 that branch off from each node. Have been.
One of the branch line transmission lines 10, 10,.
Are connected to the supervisory control station 3 via the transmission line switch 5. Similarly, branch transmission line 1 of a different system
The pairs 0 and 20 are connected to the input / output terminals 4 and 4 via the transmission line switch 5 respectively. In FIG. 1, two input / output terminals 4 and 4 are provided to simplify the illustration.
Only is shown.

The monitoring control station 3 functions as a LAN host, and each input / output terminal 4 is composed of a terminal device using the LAN. The trunk transmission lines 1 and 2 and the branch transmission lines 10 and 20 are divided into two systems, one of which is a regular transmission line for normal use, and the other is a standby transmission line used when a failure occurs in the regular transmission line. These transmission lines are respectively switched, and the systems of these transmission lines can be switched by each transmission line switch 5.

That is, as shown in the normal state in FIG. 1, each transmission line switch 5 connects the monitoring control station 3 as each communication station or each input / output terminal 4 to the service transmission line side. In this state, communication between the communication stations using the normal transmission path is possible. For example, when a failure occurs in the service transmission line, the monitoring control station 3 and the input / output terminals 4, 4 output a transmission line switching signal to the respective transmission line switching devices 5, and each transmission line switching device 5 switches the transmission path according to the transmission path switching signal.

The detection of such a fault is individually performed by the monitoring control station 3 and the input / output terminals 4 and 4. The principle of this detection will be described below.

The monitoring control station 3 and the input / output terminals 4 and 4
Outputs a transmission path confirmation signal to a currently used transmission path at a predetermined time period. This transmission path confirmation signal is
It is output irrespective of the transmission timing of the MAC frame used for the normal LAN communication, but may be synchronized with the normal MAC frame.

FIG. 2 is a schematic diagram showing a configuration of a normal MAC frame, and FIG. 3 is a schematic diagram showing a configuration of a transmission path confirmation signal. As shown in FIG. 2, a normal MAC frame includes a preamble PA, a frame start delimiter SFD,
Destination address DA, source address SA, data length D
L, data body DB, and frame inspection sequence FC
S. The number in octets of each part is shown in parentheses.

The preamble PA is a synchronization symbol added to the head of the MAC frame. Even if collision with other data is detected during transmission of the MAC frame, retransmission is performed for a time corresponding to the length of the preamble PA. Try. The frame start delimiter SFD defines the start position of the data frame. The destination address DA is the MA of the destination communication station.
C address. The source address SA is the MAC address of the communication station that is the source. The data length DL indicates the length of the following data body DB in octets. The data body DB is data itself to be transmitted. The frame check sequence FCS is a sequence for checking a frame including a CRC code.

As shown in FIG. 3, the transmission path confirmation signal is MA
The normal MAC shown in FIG.
The data body DB of the frame is blank, and a padding (pad) is inserted in this portion to make the number of octets of the entire MAC frame a specified number. This gives L
It can be implemented without changing the protocol of the physical layer of the AN. It is also possible to adopt a configuration in which information indicating a transmission path confirmation signal is inserted instead of the pad.

Such a transmission path confirmation signal is transmitted with its destination address DA as a broadcast, and the receiving station identifies the transmission path confirmation signal by referring to the data body DB.

FIG. 4 is a flowchart showing the processing contents when each communication station switches the transmission path system based on the transmission path confirmation signal. The monitoring control station 3 and each input / output terminal 4 perform the same processing. First, it is checked whether or not the transmission path confirmation signal has been received again within a predetermined time since the transmission path confirmation signal was last received from another station (step 11). As described above, this refers to the data body of the received frame, and if it is a pad, recognizes it as a transmission path confirmation signal.

If the signal is received within a predetermined time, step 11 is repeated by resetting the timer. On the other hand, when the transmission line is not received, it is determined that a failure has occurred in the transmission line of the currently used system, and a transmission line switching signal is output to the transmission line switch 5 to switch the transmission line system. (Step 12) The processing from step 11 is repeated again.

The switching of the transmission line is not limited to one direction of switching from the service transmission line to the standby transmission line, or switching from the standby transmission line to the service transmission line. For example, each time a transmission line switching signal is output, the transmission line switching unit 5 may be configured to alternately switch between a normal transmission line and a standby transmission line.

Further, the transmission path in which a fault has occurred may be specified based on the transmission source address of the received transmission path switching signal, which has not been received within the predetermined time. Further, if the failure is not of a physical type, a configuration may be adopted in which a computer program is used to perform failure diagnosis, failure recovery, and the like based on information on the specified transmission path and the like.

As described above, when the system of the transmission line is switched at one communication station, the transmission line confirmation signal from this communication station does not reach other communication stations. Switch the transmission line system one after another,
Eventually, all communication stations will again use the same transmission path.

Embodiment 2 FIG. 5 shows a bus type LAN as a system using the transmission line redundancy method according to the present invention.
It is a block diagram which shows Embodiment 2 of FIG. In the above-described first embodiment, it is necessary to execute the processing operation shown in FIG. 4 in each of the monitoring control station 3 and the input / output terminals 4 and 4. However, in the present embodiment, each transmission path switching is performed. By causing the unit 5 to perform the processing operation, the same processing as in the first embodiment can be performed without modifying software provided in the monitoring control station 3 and the input / output terminals 4 and 4.

Specifically, each transmission line switch 5 has a CPU 5
0 is provided so that the CPU 50 performs the processing operation shown in FIG.

Other configurations and operations of the present embodiment are the same as those of the first embodiment, and the same reference numerals are given to the overlapping portions, and the other description is omitted.

Embodiment 3 FIG. 6 shows a bus type LAN as a system using the transmission line redundancy method according to the present invention.
It is a block diagram which shows Embodiment 3 of FIG. The present embodiment is different from the second embodiment in that the management device 6 as one station
Are connected via a transmission line switch 5. Management device 6
Comprises a terminal device such as a computer, and has a monitor 7.

FIG. 7 is a schematic diagram showing a configuration of a transmission path confirmation signal including transmission path switching information. Further, in the present embodiment, as shown in FIG. 7, transmission line switching information indicating which of the service transmission line and the standby transmission line is in use is included in the data body of the transmission line confirmation signal. Has been added. The transmission line switching information may include information other than the information indicating which of the above-mentioned normal transmission line and the standby transmission line is being used, and the content is not limited.

The management device 6 displays the contents based on the transmission line switching information on the monitor 7. For example, after the management device 6 switches the transmission line switch 5, any of the transmission lines It is displayed whether the system is in use.

Other configurations and operations of the present embodiment are the same as those of the second embodiment, and the same reference numerals are given to the overlapping portions, and the other description is omitted.

Embodiment 4 FIG. FIG. 8 shows a bus type LAN as a system using the transmission line redundancy method according to the present invention.
It is a block diagram which shows Embodiment 4 of FIG. This embodiment is different from the first embodiment in that the monitoring and control station 3 does not include the transmission line switch 5 but includes the monitor 7 as in the third embodiment.

In this embodiment, only the supervisory control station 3 transmits a transmission path confirmation signal including transmission path switching information as in the third embodiment. Based on this, each input / output terminal 4 outputs a transmission line switching signal as in the first embodiment. On the other hand, the supervisory control station 3 receives the normal M received from each input / output terminal 4.
A similar operation is performed based on an AC frame. Next, this operation will be described.

FIG. 9 is a flowchart showing the processing contents when the monitoring control station 3 switches the transmission path. First, the source input / output terminal 4 is specified with reference to the source address of the normal MAC frame received from the input / output terminal 4 (step 21). It should be noted that the data body of the MAC frame may include information for specifying the source, and the source may be specified based on this information.

Next, it is specified whether the MAC frame has been sent via the service transmission line or the standby transmission line (step 22). This determination can be made by identifying which system of the service transmission line or the standby transmission line connected to the supervisory control station 3 has received the MAC frame. It is also possible to include the switching information of the transmission line switch 5 in the data body of the MAC frame sent from the terminal 4 and make a judgment from this switching information.

Then, a transmission path confirmation signal is transmitted via the transmission path of the specified system (step 23). If necessary, information indicating the transmission path system that transmitted the transmission path confirmation signal is transmitted to the transmission path. It is displayed on the monitor 7 as switching information (step 24).

As described above, in the present embodiment, the supervisory control station 3 does not need to include the transmission line switch 5 and transmits the transmission path confirmation signal only from the supervisory control station 3. The system configuration is simpler than that of ~ 3,
Further, the transmission path load can be reduced.

Other configurations and operations of the present embodiment are the same as those of the first embodiment, and the same reference numerals are given to the overlapping portions, and the other description is omitted.

Embodiment 5 FIG. FIG. 10 shows a bus type LA as a system using the transmission line redundancy method according to the present invention.
FIG. 35 is a block diagram showing an Nth embodiment 5; This embodiment is different from the first embodiment in that the transmission line switch 5 provided in each communication station is eliminated.

FIG. 11 is a flowchart showing the data transmission processing of each communication station, and FIG. 12 is a flowchart showing the data reception processing of each communication station. First, at the time of data transmission as shown in FIG. 11, a normal MAC frame including data to be transmitted is generated (step 3).
1) Add information specifying the storage address at the destination to the generated MAC frame, and generate two such MAC frames (step 32). Then, one data is transmitted to the service transmission line (step 33), and the other data is transmitted to the standby transmission line (step 34).

Next, when such data is received, as shown in FIG. 12, the same data is received from both transmission lines (step 41). At this time, the data is stored in the storage address included in the data without identifying from which system the transmission path is received (step 42). Therefore, even when a failure occurs in one of the transmission lines, the same data can be received from the normal transmission line.

Also, in this embodiment, the transmission path confirmation signal as shown in the first to fourth embodiments is unnecessary, and the transmitted data is stored as specified on the receiving side, so that the transmission path switching time is reduced. Is unnecessary.

Other configurations and operations of the present embodiment are the same as those of the first embodiment, and the same reference numerals are given to the overlapping portions, and the other description is omitted.

[0056]

As described above in detail, in the transmission line redundancy method and the system using the method according to the present invention,
Communication stations respectively connected to any one of a plurality of transmission lines via a switch transmit a predetermined signal in a time series and receive the predetermined signal from another communication station. When the reception of the signal is interrupted for a predetermined time, a switching instruction is output to the switch, and the switch switches the transmission path of the connected system to the transmission path of another system based on the switching instruction. With the configuration, a plurality of transmission lines are provided, and even if a failure occurs in any of the transmission lines, the transmission line can be switched to a normal transmission line, so that the entire system does not go down, After the switching, it is possible to recover the transmission path of the system in which the failure has occurred while using the system.

Further, communication stations are respectively connected to any one of a plurality of transmission lines via a switch, and each switch transmits a predetermined signal in a time-series manner. While the predetermined signal is received, when the reception of the predetermined signal is interrupted for a predetermined time, the transmission path of the connected system is switched to the transmission path of another system. Just attach the switch of the present invention to the line,
The function performed by the communication station of the above-described invention can be performed by the switch, and there is no need to change the software of the existing communication station.

Also, information indicating the switching state of the transmission line is added to the predetermined signal, and the information is displayed on display means connected to the plurality of transmission lines via the switch. In the above two inventions, the operator can visually know the switching state of the transmission path.

Further, a first system connected to a plurality of transmission lines
A communication station transmits a predetermined signal in time series, and a second station connected to one of the transmission paths of the plurality of systems via a switch.
While the communication station receives the predetermined signal, if the reception of the predetermined signal is interrupted for a predetermined time, the communication station outputs a switching instruction to the switching device, and the switching device is connected based on the switching instruction. Since the transmission path of one system is switched to the transmission path of another system, it is not necessary for the first communication station to include a switch, so that a simpler configuration can be achieved.

Further, the first system connected to a plurality of transmission lines
A communication station transmits a predetermined signal in time series, a second communication station is connected to any one of the transmission paths of the plurality of systems via a switch, and the switch receives the predetermined signal. on the other hand,
When the reception of the predetermined signal is interrupted for a predetermined time, the transmission path of the connected system is switched to the transmission path of another system. By simply attaching the switch, the function performed by the communication station of the invention described above can be performed by the switch, and there is no need to change the software of the existing communication station.

[0061] Also, a configuration in which the information related to the transmission path of the system in which the switch receives the predetermined signal is displayed on display means connected to the transmission paths of the plurality of systems via the switch. Therefore, in the above two inventions, the operator can visually know the switching state of the transmission path.

Further, since the communication station connected to the plurality of transmission lines transmits the same information via the plurality of transmission lines, there is no need to provide the switch in any of the above-mentioned inventions. The present invention has excellent effects, for example, the configuration is simple, and the switching itself can be omitted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a bus type LAN as a system using a transmission line redundancy method according to the present invention.

FIG. 2 is a schematic diagram showing a configuration of a normal MAC frame.

FIG. 3 is a schematic diagram illustrating a configuration of a transmission path confirmation signal.

FIG. 4 is a flowchart showing processing contents when each communication station switches a transmission line system based on a transmission line confirmation signal.

FIG. 5 is a block diagram showing a second embodiment of a bus type LAN as a system using the transmission line redundancy method according to the present invention.

FIG. 6 is a block diagram showing a third embodiment of a bus type LAN as a system using the transmission line redundancy method according to the present invention.

FIG. 7 is a schematic diagram showing a configuration of a transmission path confirmation signal including transmission path switching information.

FIG. 8 is a block diagram showing a fourth embodiment of a bus type LAN as a system using the transmission line redundancy method according to the present invention.

FIG. 9 is a flowchart showing processing contents when the monitoring control station switches transmission paths.

FIG. 10 is a block diagram showing a fifth embodiment of a bus type LAN as a system using a transmission line redundancy method according to the present invention.

FIG. 11 is a flowchart showing a data transmission process of each communication station.

FIG. 12 is a flowchart showing a data reception process of each communication station.

FIG. 13 is a block diagram showing a configuration of a conventional bus-type LAN.

[Explanation of symbols]

1 main line transmission line (normal system), 2 main line transmission line (standby system), 3 monitoring control station, 4 input / output terminals, 5 transmission line switch, 6 management device, 7 monitor, 10 branch line transmission line (normal system), 20 branch transmission line (standby system), 50
CPU.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B083 AA04 BB01 BB03 CC09 CD11 CE01 DD01 DD09 DD13 EE11 GG04 5K021 AA06 BB08 CC11 DD02 EE01 FF01 FF11 5K032 AA06 BA01 BA02 CC04 DA11 DB03 EA02 EA04 EB06

Claims (14)

[Claims] A communication station connected to any one of a plurality of transmission lines via a switch transmits a predetermined signal in time series and receives the predetermined signal from another communication station. On the other hand, when the reception of the predetermined signal is interrupted for a predetermined time, a switching instruction is output to the switching unit, and the switching unit switches the transmission path of the connected system to another system based on the switching instruction. A method of making a transmission line redundant, characterized by switching to a transmission line of the same type. 2. A communication station is connected to any one of a plurality of transmission lines via a switch, and each switch transmits a predetermined signal in a time-series manner. A transmission path redundancy method, comprising: when a predetermined signal is received, when the reception of the predetermined signal is interrupted for a predetermined time, a transmission path of a connected system is switched to a transmission line of another system. 3. The information indicating a switching state of a transmission line is added to the predetermined signal, and the information is displayed on a display unit connected to the transmission lines of the plurality of systems via the switch.
Or the transmission path redundancy method according to 2. 4. A first communication station connected to a plurality of transmission lines transmits a predetermined signal in time series, and is connected to one of the plurality of transmission lines via a switch. While the second communication station receives the predetermined signal, if the reception of the predetermined signal is interrupted for a predetermined time, the second communication station outputs a switching instruction to the switching device, and the switching device connects based on the switching instruction. A transmission line redundancy method characterized in that a transmission line of a system is switched to a transmission line of another system. 5. A first communication station connected to a plurality of transmission lines transmits a predetermined signal in time series, and a second communication station is connected to any one of the plurality of transmission lines via a switch. A station is connected, and the switcher receives the predetermined signal, and when reception of the predetermined signal is interrupted for a predetermined time, switches the transmission path of the connected system to the transmission path of another system. Characteristic transmission line redundancy method. 6. A method for displaying information related to a transmission path of a system in which the switching device has received the predetermined signal on display means connected to the transmission lines of the plurality of systems via the switching device. Item 6. A method for making a transmission line redundant according to Item 4 or 5. 7. A transmission line redundancy method, wherein a communication station connected to a plurality of transmission lines transmits the same information via the plurality of transmission lines. 8. A transmission system comprising: a plurality of transmission lines; a plurality of switches selectively connected to any one of the plurality of transmission lines; and a communication station performing communication via each of the switches. Each communication station, transmitting means for transmitting a predetermined signal in time series, receiving means for receiving the predetermined signal from another communication station, and when the reception of the predetermined signal by the receiving means is interrupted for a predetermined time Output means for outputting a switching instruction to the switching device, wherein each switching device is configured to switch a transmission path of a connected system to a transmission path of another system based on the switching instruction. Transmission line redundancy system characterized by the above-mentioned. 9. A transmission system comprising: a plurality of transmission lines; a plurality of switching units selectively connected to any one of the plurality of transmission lines; and a communication station performing communication via each of the switching units. Each switch includes a transmitting unit that transmits a predetermined signal in time series, and a receiving unit that receives the predetermined signal from another switch,
When the reception of the predetermined signal by the receiving means is interrupted for a predetermined time, a transmission line of a connected system is switched to a transmission line of another system. 10. The transmission according to claim 8, further comprising an adding unit for adding information indicating a switching state of a transmission line to the predetermined signal, and a display unit connected to the communication line and displaying the information. Road redundancy system. 11. A transmission line of a plurality of systems, a first communication station connected to the transmission lines of the plurality of systems and transmitting a predetermined signal in time series, and one of the transmission lines of the plurality of systems is selected. And a second switch for performing communication via the switch.
A communication station, wherein the second communication station receives the predetermined signal, and an output for outputting a switching instruction to the switch when reception of the predetermined signal by the reception means is interrupted for a predetermined time. Means, and wherein the switch is configured to switch the transmission path of the connected system to the transmission path of another system based on the switching instruction. 12. A transmission line of a plurality of systems, a first communication station connected to the transmission lines of the plurality of systems and transmitting a predetermined signal in time series, and one of the transmission lines of the plurality of systems. A switch for selectively connecting, and a second communication station for performing communication via the switch, wherein the switch includes a receiving unit for receiving the predetermined signal, and the receiving unit receives the predetermined signal. A transmission line redundancy system, wherein, when reception is interrupted for a predetermined time, a transmission line of a connected system is switched to a transmission line of another system. 13. The system according to claim 11, further comprising a display unit connected to said plurality of transmission lines via said switch, said display unit displaying information relating to the transmission line of the system that has received said predetermined signal. Or the transmission line redundancy system according to 12. 14. A communication system comprising: a plurality of transmission lines; and a plurality of communication stations connected to the plurality of transmission lines, wherein each communication station transmits the same information via the plurality of transmission lines. A transmission line redundancy system, characterized in that: