JP2003018172A - Network system and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contract the time required, until the recovery of a transmission, when abnormalities are generated in transmission lines or in transmission equipment. SOLUTION: In loop-type transmission lines L1, L2, whose transmitting directions face in opposite directions to each other, transmission equipment (master equipment 1 and processor equipment 2-6) are connected in series with each other. In such a network system, each transmission equipment transmits carrier signals on transmission lines L1, L2 to its downstream transmission equipment, and e.g. when abnormalities are generated between the processor equipment 4, 5 to interrupt the carrier signals, the downstream-side transmission equipment 4, 5 report the abnormalities of the transmission lines to the master equipment 1. Then, the master equipment 1 edits telegraphic messages of starting loop-backs, so as to transmit them to both the transmission lines L1, L2. The processor equipment 4, 5 receive the telegraphic messages and set their control states to loop-back modes with detour circuits being formed. Thereby, data transmission by the loop-backs is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network system in which a plurality of transmission devices are connected to a double loop transmission line, and a network system control method.

[0002]

2. Description of the Related Art Various dual-loop network systems have been considered, and the basic configuration is such that one master station transmission device (master device) and a plurality of slave station transmission devices (processor devices) are provided. It is connected to a loop transmission line,
The two loop-shaped transmission lines are configured such that their transmission directions are opposite to each other in consideration of loopback.

Usually, one of the looped transmission lines is used as an active system for transmitting application data, and the other is used as a standby system. Then, when there is an abnormality in the operating system or when there is a planned switching instruction, loop alternation control for switching the operating system and the standby system is executed, and an abnormality occurs in the transmission line or the transmission device. When transmission is not possible as a loop transmission line, loopback control is generally executed in which transmission is performed only by a normal device, bypassing the transmission line of an abnormal device.

As a control for such an abnormality, Japanese Patent Laid-Open No. 9-
According to Japanese Patent No. 326816, when a reception state is monitored and an abnormality is found, output stop and detour route configuration control are performed in each processor device, and after a lapse of a predetermined time, a master device checks the transmission state and finally It has been proposed to send a dynamic switch decision command.

Further, Japanese Patent Laid-Open No. 8-65328 discloses that
As a method of detecting an abnormality in the transmission path, by extending the control unit of the transmission data to add information for error detection, transmitting the above data at a fixed cycle, and monitoring the reception status in the downstream device. A device that detects an error in the transmission line detects the error and sets the additional information and sends it downstream, so that the master device detects the line error and where it occurred, and issues a loop change or loopback instruction. Is proposed.

[0006]

However, in the case of Japanese Unexamined Patent Application Publication No. 9-326816 among the above-mentioned conventional techniques, the processor device that detects an abnormality configures a detour by itself, and when an abnormality occurs, all processors are processed. There is a problem that it takes time from the occurrence of an abnormality to the recovery because the master device performs the final determination after the configuration of the device is changed sequentially and the states of all the processor devices are stabilized.

Further, in the case of Japanese Patent Laid-Open No. 8-65328, since the abnormality determination is made because the abnormality detection data is not received, it is necessary to perform timer monitoring of the non-communication time of the transmission cycle of the error detection data or more. However, there is a problem that it takes time for that.

In the system in which the master device centrally monitors the abnormality on the line and gives an instruction, if the transmission does not recover according to the instructed content, the transmission is finally recovered because the retry is performed after the status is confirmed again. It takes time to do.
In a signal control network for railways, transmission failure causes an immediate stoppage of operation and, in the worst case, an accident. Therefore, it is necessary to restore the transmission in a much shorter time than a general network.

It is an object of the present invention to shorten the time required for transmission restoration when an abnormality occurs in a transmission line or a transmission device.

[0010]

In order to solve the above problems, according to the present invention, one master station transmission device and a plurality of slave station transmission devices are connected to two loop type transmission lines whose transmission directions are opposite to each other. In the network system in which one of the loop type transmission lines is used as an active system and the other transmission line is used as a standby system, and communication is performed between the transmission devices, the transmission line is directed toward the transmission device on the downstream side. Carrier signal transmitting means for transmitting a carrier signal to the master station, monitoring means for monitoring the reception of the carrier signal and, if there is an interruption in the carrier signal, monitoring means for notifying the master station transmission device of a transmission path abnormality, and the master station transmission. It is installed in the device and receives the transmission line abnormality notification to determine the failure point on the transmission line, and when abnormality is reported on both transmission lines, the loopback start message is edited and both transmission lines are edited. And a loopback mode setting unit that is provided in the slave station transmission device and that receives a message from the master station transmission device and sets the transmission control state to a loopback mode, The master station transmission device is provided with a determining means for transmitting a telegram for confirmation of opening to the transmission path after a predetermined time has elapsed from the transmission of the telegram, and for determining that loopback is completed when the telegram is returned. It has a feature.

According to the above configuration, when an abnormality occurs in the transmission line, the notification of the transmission line abnormality is immediately transmitted to the master station transmission device. Especially when an error occurs on both transmission lines,
The slave station transmission device that has detected the abnormality does not form a detour by itself, and all notifications of the transmission path abnormality are transmitted to the master station transmission device. Then, the master station transmission device receives the notification of the transmission path abnormality, edits the telegram of the loopback start, and sends the telegram to both transmission paths, so the slave station transmission device receives the telegram and transmits it immediately. The control state can be set to loopback mode. As a result, data transmission by loopback becomes possible, and the time until the transmission is restored can be shortened.

In the above configuration, when the master station transmission device is notified of an abnormality on only one transmission line, a loop alternation mode for switching the transmission line between the active system and the standby system is set.

Further, when the opening confirmation message is not returned, the master station transmission device edits the loopback start message with the minimum detour configuration information defined in advance in the system, and retransmits it.

Further, the following elements can be added to the network system having the above configuration. That is,
A loop check message transmitting means, which is provided in the master station transmission device, transmits a loop check message to both transmission lines in a predetermined cycle to check whether or not the failure of the transmission line is recovered, and the slave station transmission device, Loop check message receiving / transmitting means for receiving the loop check message and transmitting the loop check message to the transmission line of the receiving side, and the master station transmission device are provided, and the loop check message is transmitted on both transmission lines. A loopback release message sending means for sending a loopback release message to both transmission lines when returning, and a transmission control state in the normal mode when the loopback release message is received in the slave station transmission device. And a normal mode setting means for setting.

Also, in the network system control method of the present invention, one master station transmission device and a plurality of slave station transmission devices are connected to two loop type transmission lines whose transmission directions are opposite to each other, and the loop type transmission line is connected. Among them, one transmission path is used as an active system and the other transmission path is used as a standby system, and when controlling a network system for performing communication between the transmission devices, a carrier is provided on the transmission line toward a downstream transmission device. While transmitting a signal, if the carrier signal is interrupted by monitoring the reception of the carrier signal, a transmission path abnormality is notified to the master station transmission device, and the master station transmission receives the transmission path abnormality notification. The device determines the failure point on the transmission line from the notification of the transmission line error, and when an error is reported on both transmission lines, edits the loopback start message and sends it to both transmission lines. However, the slave station transmission device that has received the loopback start message, while setting the transmission control state to the loopback mode, the master station transmission device, a predetermined time after transmitting the loopback start message It is characterized in that after the lapse of time, an opening confirmation message is transmitted to the transmission line, and when the opening confirmation message is returned, it is determined that the loopback is completed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a network system according to the present invention. This network system includes one master device M as a master station transmission device,
Five processor devices P1 to P5 are installed as slave station transmission devices, and a master device M and processor devices P1 to P5 are installed.
5 are connected by double loop-shaped transmission lines L1 and L2 whose transmission directions are opposite to each other. Note that the number of processor devices is not limited to five, and may be two to four, or six or more. In the following description, the master device M will be referred to as the master device 1, and the processor devices P1 to P5 will be referred to as the processor devices 2 to 6, respectively.

FIG. 2 shows the internal structure of the transmission device, which is the master device 1 or the processor devices 2 to 6. The transmission device is a 1-system CPU 20A and a 2-system CPU 20B.
And NCP 22A, 22B connected to CPU 20A
And the NCP 22C, 22D connected to the CPU 20B
And NIF24A connected to NCP22A, 22C
And an NIF 24B connected to the NCPs 22B and 22D.

The CPUs 20A and 20B are processors for executing application processing, which are connected to each other through an inter-CPU communication path 21 and exchange state information or control information.
Executes dual function. NCP22A, 22B, 22
C and 22D are network controllers that control the communication of the transmission line, and NCPs 22A and 22C are the transmission line L1.
The NCPs 22B and 22D control the transmission line L2, respectively. Further, the NCPs 22A and 22B are the communication paths 23 between the NCPs.
In A, the NCPs 22C and 22D are respectively connected by the inter-NCP communication path 23B, and bidirectionally transmit and receive electronic messages.
The NIFs 24A and 24B are network interfaces that control input and output to and from the transmission lines L1 and L2, respectively.

In the following description, the CPUs 20A, 2
0B are collectively referred to as CPU 20, NCP 22A, 22B,
22C and 22D are collectively referred to as NCP22 and NIF24.
A and 24B are collectively called NIF24.

FIG. 3 shows the internal structure of the NIF 24. The NIF 24 includes the NCP I / F 31 and the selector 3
2, a receiver 33, and a driver 34.
The NCP I / F 31 is an NCP22 (NCP22A, 22
C and NCP 22B, 22D), and has data transmission / reception, mode setting and monitoring functions. The receiver 33 and the driver 34 are connected to the transmission lines L1 and L2 and control the reception and transmission of data, respectively. The selector 32 receives the data received from the receiver 33 or NC.
The transmission data from the P I / F 31 is transferred to the NCP I / F 31
It has a function of selectively selecting and outputting to the driver 34 under the control of.

FIG. 4 shows a transmission / reception data format. As shown in the figure, the transmission / reception data includes a start flag 40 for bit synchronization, a transmission source address 41, a function code 42, a data section 43, a frame check sequence 44 (FCS), and an end flag 45.

Next, the operation of the network system having the above configuration will be described. First, a procedure for receiving data from another device will be described with reference to FIGS. 5 and 6. When the NCP 22 is not performing transmission processing, the NCP 22
The selector 32 of 24 is set to a mode (through mode) for selecting the data received from the receiver 33. NIF
24 electrically relays the received data, and the driver 34
To the transmission line L1 or L2 via
Received data is sent to the NCP 22 via the CP I / F 31.

The NCP 22 checks the frame of the received data that has been sent, checks the function code if it is a normal frame, searches the preset function code table, and if they match, the CPU shared memory Set the received data to. When the frame of the received data is abnormal or the function code does not match, the received data is discarded.

The procedure of data transmission will be described with reference to FIGS. When the NCP 22 receives a transmission request from the CPU 20,
The selector 32 of the NIF 24 blocks the received data to N
Set to the mode (S & F mode) for selecting the transmission data from the CP I / F 31. After confirming the switching of the selector 32, the NCP 22 activates the feedback monitoring timer T1 and sends the transmission data to the NIF 24 (FIG. 7).

When the transmission data goes around the loop transmission line (transmission line L1 in this case) and returns to the transmission source, the data is sent from the NIF 24 to the NCP 22 (FIG. 8). NCP22
Checks the transmission source address of the received data, and if it is the address of its own device, it judges that the transmission data is returned and returns N
The selector 32 of the IF 24 is returned to the through mode, the feedback monitoring timer T1 is canceled, and the transmission process is normally terminated. When the feedback monitoring timer T1 times out without the feedback of the transmission data, the NCP 22 abnormally terminates the transmission process as transmission data non-feedback.

The data received during the transmission processing by the NCP 22 is drawn into the NCP 22 without being electrically relayed because the selector 32 of the NIF 24 is held in the S & F mode (FIGS. 9 and 10).

The NCP 22 checks the frame of the data received in the S & F mode, and if the frame is abnormal, discards the received data. As a result of the frame check, if the frame is a normal frame, it is retransmitted following the data being transmitted. If it is a normal frame, the function code is checked, and if the function code table set in advance by the CPU 20 is searched and they match, the received data is set in the CPU shared memory.

One of the dual loop transmission lines is an active system and the other is a standby system, and an application message exchanged between transmission devices is transmitted to the active transmission line. The master device 1 gives instructions for the operating system and the standby system. The master device 1 periodically switches the transmission line system once a day, and also uses a terminal (not shown) to instruct the transmission line by an operator's operation instruction. The system is switched and the loop replacement is performed.

In the processor devices 2 to 6, the transmission system that has received the application message from the master device 1 is recognized as the active system, and when there is a transmission request from the own device, it is transmitted to the recognized active system. .

Next, the procedure for performing the loop alternation in the case of abnormal transmission will be described with reference to FIGS. 11 and 12. When an abnormality occurs in the transmission lines L1 and L2 or the transmission device (NIF in the master device 1 or the processor devices 2 to 6),
Since the transmission data cannot loop back through the transmission lines L1 and L2 and return, the NCP detects a feedback timeout error in the transmission process and notifies the master device 1 of the feedback timeout error.

When the CPU of the master device 1 is notified of the transmission data feedback timeout by the NCP, it determines that the transmission line is abnormal and switches the transmission line between the active system and the standby system. For example, in FIG. 11, when the transmission line L1 is the active system,
When an abnormality occurs in the NIF on the L1 side of the processor device 4, a transmission data feedback timeout is detected in the transmission process of the master device 1, and transmission is performed with the L2 side as the active system, as shown in FIG. The processor device recognizes the switching of the transmission loop by receiving the application message of the master device which has been recognized as the standby system.

Here, detection of a line abnormality will be described.
The NIF driver 34 constantly transmits a carrier signal to the transmission lines L1 and L2. And the NIF receiver 3
3 monitors the carrier signal from the NIF on the upstream side of the transmission lines L1 and L2, and when the carrier signal is interrupted, N
The NCP is notified of the carrier disconnection via the CP I / F unit 31.

Since all the NIFs transmit the carrier signal and the NIFs on the downstream side receive the carrier signals, the abnormality in the transmission lines L1 and L2 is detected only in the NIF immediately downstream of the abnormal portion, and is detected in the NIF further downstream. do not do.

Further, the line abnormality notification will be described.
The NCP monitors the carrier disconnection signal from the NIF, and when the carrier disconnection is detected, the NCP of the processor device transmits a line status message to the master device on the transmission path in which the carrier disconnection is detected.

For example, in FIG. 13, the processor device P
When an abnormality occurs in the transmission line L1 between the P3 and P4, the carrier disconnection is detected by the NIF of the processor device P4 and the NCP is detected.
And the NCP of the processor device P4 notifies the transmission line L1.
The line status message is sent to.

Further, as shown in FIG. 14, when an abnormality occurs in the transmission line L2 between the processor devices P3 and P4,
The processor device P3 transmits the line status message to the transmission line L2.

Next, the procedure of the loopback start control of the master device will be described with reference to FIGS. After receiving the line status message, the master device 1 performs the following procedure (10
The control of loop alternation or loop back is executed in 0) to (110). If the NIF of the master device 1 detects the carrier disconnection, the line abnormality message is not transmitted. However, in the following description, the line state message reception means the master device 1
It also includes the case where carrier disconnection is detected by NIF. (100) Check the status of the transmission path on the opposite side to the transmission path on which the line status abnormal message was received, and if the line status abnormal message is not received on the opposite side transmission path, the operating loop and the standby loop To replace. (101) The loop control mode is set to the loop back transition. (102) The transmission source address is extracted from the line status abnormal message, and the device number of the device that has detected the line error is obtained from the predefined network allocation table (Table 1). For example, if the source address of the received line abnormality message is 41,
It is determined that the abnormality is detected in the device number 5 (processor device P4).

[0038]

[Table 1]

(103) From the device number of the line abnormality detecting device of both transmission lines L1 and L2 and the pre-defined detour configuration table (Table 2), the address of the device forming the detour is obtained, and the detour configuration data is obtained. To record. For example, if the abnormality detection device on the L1 side is 5 and the abnormality detection device on the L2 side is 4, the detour designation is 4: 5, that is, the device number 4 (processor device P
3) Detour from transmission line L1 to transmission line L2, device number 5
The (processor device P4) determines that there is a detour from the transmission line L2 to the transmission line L1.

[0040]

[Table 2]

(104) If the detour designation is not defined in the detour configuration table, it is determined that the loopback is not possible, and the loop control mode is set to the loop stop of both systems to finish. (105) According to the recorded detour configuration data, the instruction of the device forming the detour is edited into a loopback start instruction message. In the loopback start instruction message, the address of the device detouring from the transmission line L1 to the transmission line L2 and the address of the device detouring from the transmission line L2 to the transmission line L1 are set. (106) Send the loopback start instruction message to both transmission lines L
1, L2, and start timer T2 (Fig. 1
5). (107) After the timer T2 times out, an opening confirmation message is transmitted to the transmission line L1 and the timer T3 is started. (108) When the opening confirmation message is returned, the loop control mode is set to the loop back control (FIG. 17). (109) Timer T3 without opening confirmation message
If the time-out has occurred and the instruction of the detour configuration is the minimum detour configuration defined in advance (FIG. 22), the loop control mode is set to stop both loops and the process is terminated. (110) Timer T3 without opening confirmation message
If the time-out occurs and the detour configuration instruction is not the minimum detour configuration, a device that configures the detour is obtained according to a predefined minimum detour configuration table, recorded in the detour configuration data, and the process returns to step (105). .

The procedure of loopback start control of the processor unit will be described. After receiving the loopback start instruction message from the master device, the processor device executes the loopback control in the following steps (200) to (203). (200) Set the loop control mode to loop back transition. (201) The received loopback start instruction message is NC
Transfer to the NCP on the opposite loop side using the P-to-P communication path (FIG. 16). (202) The detour configuration device of the loopback start instruction message is checked, and if it is its own device, the NIF is set to the S & F mode, and the loopback start instruction message is detoured from the transmission line L1 to the transmission line L2 (see FIG. 19), or according to the detour (FIG. 20) instruction from the transmission line L2 to the transmission line L1, the NCP
Set up a communication path between them. (203) After receiving the opening confirmation message, the loop control mode is changed to the loopback transition.

The operation during loopback control will be described. The master device transmits a loop check message to both transmission paths at a system-specified cycle. The processor device sends the received loop check message to the received loop side without detouring to the opposite loop side (FIG. 18).
Therefore, when the failure of the transmission path is recovered, the loop check message is returned to the master device.

Next, the procedure for canceling the loopback of the master device will be described. When the loop check message is returned on both transmission lines, the master device performs the following procedure (30
The loopback cancellation control is executed in 0) to (303). (300) Set the loop control mode to the loopback canceling state. (301) Send a loopback release message to both transmission lines and activate the feedback timeout monitoring timer T1 (FIG. 21). (302) When the loopback release message is returned, the loop control mode is set to the normal mode. (303) If the loopback release message does not return and the feedback timeout monitoring timer T1 times out,
The loop control mode is set to the transition to the loopback, and the control to start the loopback is performed again according to the detour configuration data.

A loopback cancellation procedure of the processor unit will be described. When the processor device receives the loopback release message from the master device, the processor device performs the following procedure (40
The loopback cancellation control is executed in 0) to (401). (400) Set the loop control mode to the normal mode. (401) In the processor device forming the detour,
Cancel the communication path between NCPs set in step (202),
Send the received loopback release message to the receiving loop side.

According to this embodiment, the following effects can be expected. As shown in FIG. 23, since each component of the transmission device is configured in a dual system, one system (for example, NCP2
Even when an abnormality occurs in 2A), the transmission control can be continued in the remaining other system (for example, NCP 22C and 22D). As described in the procedure of data transmission / reception, S & F
Since the device which has entered the mode discards the data having the frame abnormality, the data having the frame abnormality during the transmission is appropriately removed. As explained in the procedure for loop replacement, the master device manages the switching between the active system and the standby system, and the processor device recognizes the application message reception loop from the master device as the active system. No special transmission procedure is required. As described in the line abnormality detection procedure, the carrier signal is monitored between each NIF of the transmission line. Therefore, if an abnormality occurs on the line, only the downstream device adjacent to the abnormal point can detect the abnormality. The location can be easily specified. Since the NCP carries out line status monitoring at its own timing, it is possible to promptly detect and notify the occurrence of an abnormality without the need for control from the master device or the CPU. As described in the loopback start control procedure, the device to be looped back is determined from the line state aggregated in the master device, so that the determination of the abnormal portion and the identification of the bypass device can be performed quickly. If the detour configuration cannot be taken, the system shifts to the minimum detour configuration that is predefined in the system, so that the transmission can be recovered with the minimum equipment required for system operation, and the transmission interruption time can be minimized. it can. As described in the procedure for canceling the loopback, the master device periodically performs the loop check, so that the recovery of the transmission path can be automatically detected. As shown in FIG. 21, since the loopback release message is transmitted without circumventing both loops, transmission of all devices on the loop transmission line, including devices located outside the transmission line during loopback, is performed. The state can be reset.

[0047]

As described above, according to the present invention,
When an abnormality occurs in the transmission line or the transmission device, the loopback mode is set immediately, so that the time until the transmission is restored can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a network system according to the present invention.

FIG. 2 is a transmission device (master device or processor device)
FIG.

FIG. 3 is a configuration diagram of an NIF.

FIG. 4 is a diagram showing a data format of transmission / reception data.

FIG. 5 is a diagram showing a data reception path in a transmission device.

FIG. 6 is a diagram showing a data reception path inside the NIF.

FIG. 7 is a diagram showing a data transmission path in a transmission device.

FIG. 8 is a diagram showing a data flow when data is returned in the transmission device.

FIG. 9 is a diagram showing a data flow during S & F in the NIF.

FIG. 10 is a diagram showing a data flow in S & F in the transmission device.

FIG. 11 is a diagram showing a state in which an abnormality has occurred in the active system.

FIG. 12 is a diagram showing a state in which a standby system is changed from the state shown in FIG. 11 to a loop system.

FIG. 13 is a diagram showing how the master device is notified of a line abnormality of a transmission line L1.

FIG. 14 is a diagram showing a state in which a line abnormality of a transmission line L2 is notified to a master device.

FIG. 15 is a diagram showing how a loopback start instruction message is being transmitted.

FIG. 16 is a diagram showing how the received loopback start instruction message is transferred to the NCP on the opposite loop side.

FIG. 17 is a diagram showing a data flow during loopback control.

FIG. 18 is a diagram showing how a loop check message is being transmitted.

FIG. 19 is a diagram showing a loopback route from the transmission line L1 to the transmission line L2.

20 is a diagram showing a loopback route from the transmission line L2 to the transmission line L1. FIG.

FIG. 21 is a diagram showing how a loopback cancellation message is being transmitted.

FIG. 22 is a diagram showing a minimum detour configuration.

FIG. 23 is a diagram showing a bypass route when an abnormality occurs in one system.

[Explanation of symbols]

1 Master device 2-6 Processor device L1, L2 Loop transmission line 20A, 20B CPU 21 CPU transmission line 22A-22D NCP (network controller) 23A, 23B NCP transmission line 24A, 24B NIF (network interface) 31 NCP I / F 32 Selector 33 Receiver 34 Driver

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Chiba             1070 Ichimo, Hitachinaka City, Ibaraki Prefecture Stock Association             Hitachi, Ltd. Transportation Systems Division Mito Transportation             System headquarters (72) Inventor Masakazu Sonobe             2-2-2 Yoyogi, Shibuya-ku, Tokyo Tohnichi             Inside the passenger railway (72) Inventor Manabu Nishio             2-2-2 Yoyogi, Shibuya-ku, Tokyo Tohnichi             Inside the passenger railway (72) Inventor Takashi Kunifuji             2-2-2 Yoyogi, Shibuya-ku, Tokyo Tohnichi             Inside the passenger railway (72) Inventor Yuichiro Tora             2-2-2 Yoyogi, Shibuya-ku, Tokyo Tohnichi             Inside the passenger railway F term (reference) 5K031 AA08 DA02 DA12 EA03 EA10                       EA12 EB05 EB12

Claims (5)

[Claims] 1. A master station transmission device and a plurality of slave station transmission devices are connected to two loop type transmission lines whose transmission directions are opposite to each other, and one transmission line of the loop type transmission lines is operated. And a carrier signal transmitting means for transmitting a carrier signal on a transmission line toward a transmission device on the downstream side, and the carrier signal. Monitoring means for notifying the master station transmission device of a transmission path abnormality if the carrier signal is interrupted, and the master station transmission apparatus is provided with a monitoring means for receiving the transmission path abnormality notification and transmitting it. In addition to determining the failure point on the road, if an error is reported on both transmission lines, edit the loopback start message and send it to both transmission lines.
Transmitting means, a loopback mode setting means provided in the slave station transmission device for receiving a message from the master station transmission device and setting a transmission control state to a loopback mode, and provided in the master station transmission device And a determining unit that transmits a message confirming the opening to a transmission path after a predetermined time has elapsed from the message transmission, and determines that loopback is completed when the message is returned. 2. The network system according to claim 1, wherein when the opening confirmation message does not return, the master station transmission device uses a minimum detour configuration information predefined in the system to start a loopback message. A network system characterized by editing and transmitting again. 3. The network system according to claim 1, wherein a loop check message, which is provided in the master station transmission device and checks whether or not a failure of the transmission line is recovered, is transmitted to both transmission lines at a predetermined cycle. Loop check message transmitting means, provided in the slave station transmission device, while receiving the loop check message, the loop check message, the loop check message receiving and transmitting means for transmitting to the transmission path of the receiving, and the Provided in the master station transmission device, when the loop check message is returned in both transmission lines, loopback cancellation message transmission means for transmitting a loopback cancellation message to both transmission lines, and provided in the slave station transmission device And a normal mode setting means for setting the transmission control state to the normal mode when the loopback release message is received. Network system and butterflies. 4. The network system according to claim 1, wherein the message edit / transmission means switches a transmission path between an active system and a standby system when an abnormality is reported in only one transmission path. A network system characterized by transmitting the electronic message of the above to a transmission line. 5. A master station transmission device and a plurality of slave station transmission devices are connected to two loop type transmission lines whose transmission directions are opposite to each other, and one transmission line of the loop type transmission lines is operated. System and the transmission path as a standby system, and when controlling the network system that performs communication between the transmission devices, the carrier signal is transmitted on the transmission line toward the transmission device on the downstream side, and the carrier signal is transmitted. If there is an interruption in the carrier signal by monitoring the reception of the, the transmission path abnormality is notified to the master station transmission apparatus, and the master station transmission apparatus that has received the transmission path abnormality notification is In addition to determining the failure point on the transmission line, if an error is reported on both transmission lines, edit the loopback start message and send it to both transmission lines, and receive the loopback start message. Previous The slave station transmission device sets the transmission control state to a loopback mode, while the master station transmission device transmits a communication confirmation message to the transmission path after a predetermined time has elapsed after transmitting the loopback start message. A method for controlling a network system, characterized in that it is judged that the loopback is completed when the message for confirming the opening is returned.