JP4970336B2 - Transmission system, transmission apparatus, and transmission method - Google Patents

Description

  The present invention relates to a transmission system, a transmission apparatus, and a transmission method that can avoid a failure that occurs in communication between networks.

Conventionally, transmission device control / monitoring is performed by an Ethernet work using an Ethernet frame. When a failure occurs on the transmission device or the line, if the transmission device is directly connected to the Ethernet work, the failure is avoided by directly operating the transmission device. On the other hand, if the transmission device cannot be connected via Ethernet, a person goes directly to the transmission device. Alternatively, one of a plurality of lines connecting between transmission apparatuses is used to avoid a failure by using a spanning tree or rapid spanning tree protocol (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2005-102012

  However, it is difficult to connect an Ethernet work directly to a transmission apparatus installed in the mountains. When an obstacle occurs, it is necessary for a person to go directly, but it took time to avoid the obstacle.

Further, in the method of avoiding a failure by using one of a plurality of transmission lines connecting between transmission apparatuses of the prior art for Ethernet work, the line accommodation is performed because one line for transferring a main signal between the transmission apparatuses is occupied. On the other hand, there was a problem of inefficiency. On the other hand, in the case of spanning tree, it took time to switch from a failure to a normal line. Further, even in the case of a rapid spanning tree with improved switching time, it is necessary to create a transmission path having a structure that does not terminate an Ethernet work because it cannot be switched quickly unless a LINK disconnection is detected when a failure occurs.

  SUMMARY OF THE INVENTION In view of the above-described problems of the prior art, an object of the present invention is to provide a technique capable of avoiding a failure occurring during transmission in a short time without deteriorating line accommodation efficiency between networks.

In order to solve the above-described problem, the present invention provides a transmission system including two transmission apparatuses connected to each other by a plurality of transmission paths so as to perform communication between networks, and one transmission apparatus is A network interface unit for transferring a main signal from a network connected to one transmission device via a plurality of transmission lines to the other transmission device or from the other transmission device to a network connected to the one transmission device; a switching unit that selects one of the transmission path of the transmission line to establish the in-band communication with other transmission apparatus, a transmission path respective operating state information a plurality of transmission apparatus other hand the transfer of an extraction unit that extracts from the main signal from other transmission device, based on the extracted information of the operating condition of the other transmission device and a control unit for monitoring the operation state of the other transmission devices, other A transmission apparatus is a network interface unit that transfers a main signal from one transmission apparatus to a network connected to the other transmission apparatus or from the network connected to the other transmission apparatus to one transmission apparatus via a plurality of transmission paths. And an analysis unit for examining the operation state of the other transmission device, and an addition unit for transferring information on the operation state of the other transmission device to the main signal that is transmitted through each of the plurality of transmission paths and directed to the one transmission device. Further, the control unit determines whether or not a failure has occurred in the transmission path selected by the switching unit based on the operation state of the other transmission apparatus, and operates normally with respect to the switching unit according to the determination result. In-band communication is performed by switching to another transmission line.

  In this invention, the adding unit adds information on the operating state of the other transmission device to the overhead of the SDH frame of the main signal going to one transmission device, and the extracting unit adds the main signal from the other transmission device. Information on the operating state of the other transmission apparatus is extracted from the overhead of the SDH frame.

In this invention, the control unit monitors the operation state of the other transmission device, checks the operation state of one transmission device, and determines the operation state of one transmission device and the other transmission device by the switching unit. It is determined whether or not a failure has occurred in the selected transmission path.

  In the present invention, the two transmission apparatuses are wavelength division multiplexing apparatuses.

The present invention also relates to a transmission apparatus that receives information on the operating state of the other transmission apparatus among two transmission apparatuses connected to each other by a plurality of transmission paths so as to perform communication between networks. A network interface unit for transferring a main signal from a network connected to the own apparatus through a plurality of transmission paths to the other transmission apparatus or from the other transmission apparatus to a network connected to the own apparatus; and a plurality of transmission paths A switching unit that selects one of the transmission paths and establishes in-band communication with the other transmission apparatus, and the other transmission apparatus that transfers information on the operating state of the other transmission apparatus to each of the plurality of transmission paths And a control unit for monitoring the operating state of the other transmission device based on the extracted operating state information of the other transmission device . Further, the control unit determines whether or not a failure has occurred in the transmission path selected by the switching unit based on the operation state of the other transmission apparatus, and operates normally with respect to the switching unit according to the determination result. In-band communication is performed by switching to another transmission line.

The present invention also relates to a transmission apparatus for notifying one of the transmission apparatuses of information on the operation state of the own apparatus among two transmission apparatuses connected to each other by a plurality of transmission paths so as to perform communication between networks. The main signal is transferred from one transmission apparatus to a network connected to the own apparatus or from the network connected to the own apparatus to one transmission apparatus via a plurality of transmission paths , and the one transmission apparatus a network interface unit for performing in-band communication with, added to the own and analyzer to check the operating state of the apparatus, the main signal toward the information in the operation state of the self apparatus to the plurality of transmission paths respectively forwards one of the transmission device And an additional unit.

The present invention also relates to a transmission method in a transmission system including two transmission apparatuses connected to each other by a plurality of transmission paths so as to perform communication between networks, wherein one transmission apparatus transmits a plurality of transmissions. a step to establish a in-band communication between the selected and the other transmission apparatus of one of the transmission path of the road, the other transmission device, the steps of examining the operation state of the apparatus, the other transmission device A step of transferring the information on the operation state of the own device to a main signal that is transferred to each of the plurality of transmission paths and directed to one of the transmission devices, and one of the transmission devices has a plurality of pieces of information on the operation state of the other transmission device. extracting from the main signal from other transmission device for transferring each transmission path, one transmission device, based on the extracted information of the operating condition of the other transmission device the operating state of the other transmission device A step of viewing, one transmission device, based on the operating state of the other transmission device determines whether failure has occurred in the transmission path selected, operating normally in accordance with the determination result Switching to another transmission line and performing in-band communication .

  According to the present invention, a failure occurring during transmission can be avoided in a short time without deteriorating the line accommodation efficiency between networks.

  FIG. 1 is a conceptual diagram of a transmission system according to an embodiment of the present invention. In this embodiment, as shown in FIG. 1, it is a transmission system comprising a pair of transmission apparatuses 3a and 3b for transferring a main signal between networks 1a and 1b. In the present embodiment, the transmission devices 3a and 3b are wavelength division multiplexing (WDM) devices that are connected to each of the networks 1a and 1b via four optical fiber lines and transfer main signals. The transmission apparatuses 3a and 3b are connected by a WDM line 10 that transmits a main signal at four wavelengths with one optical fiber. The main signal transfer method in this embodiment is based on the SDH (Synchronous Digital Hierarchy) method. In the SDH system, main signals are transferred using a frame 20 having a structure as shown in FIG. The frame 20 includes an overhead 21 and a payload 22 in which a main signal is written.

  The transmission device 3a includes input / output interfaces (I / F) 4a to 4d, a switching unit 5, a storage device 6, a control unit 7, and a multiplexing / dividing unit 8. Further, the transmission device 3a is connected to the terminal 2 for displaying the operation state of the transmission devices 3a and 3b in a format that can be confirmed by the user and receiving a command from the user via an Ethernet work line. The terminal 2 can be a general workstation or a personal computer.

  The input / output I / Fs 4a to 4d are network interfaces respectively connected to four lines that transfer main signals between the network 1a and the transmission device 3b.

  The switching unit 5 is a switch such as a layer 2 switch. In the present embodiment, the switching unit 5 does not cause an Ethernet packet storm or the like, and performs in-band communication with the transmission apparatus 3b based on commands from the control unit 7 to input / output I / Fs 4a to 4d. Select one of them to switch.

  The storage device 6 stores a control program in which the control unit 7 controls the transmission device 3a, a history database regarding the operation states of the transmission devices 3a and 3b, and the like. Programs and data stored in the storage device 6 can be referred to as appropriate from the control unit 7. As the storage device 6, a flash memory, an EEPROM (Electrically Erasable Programmable Read-Only Memory), or the like can be selected and used.

  The control unit 7 controls the operation of the transmission device 3a, monitors the operation state of the transmission device 3a or 3b via the switching unit 5, and performs an operation to avoid any failure. A general CPU or the like can be used for the control unit 7.

  The multiplexing / dividing unit 8 multiplexes the main signal from the network 1a with four wavelengths and transmits it to the WDM line 10, or divides the optical signal from the WDM line 10 into four wavelengths.

  On the other hand, the transmission device 3b includes input / output I / Fs 4e to 4h, a multiplexing / dividing unit 11, a switching unit 12, and a control unit 13.

  Input / output I / Fs 4e to 4h are network interfaces respectively connected to four lines for transferring main signals between the network 1b and the transmission device 3a, and are the same as the input / output I / Fs 4a to 4d.

  The multiplexing / dividing unit 11, like the multiplexing / dividing unit 8, multiplexes the main signal from the network 1 b with four wavelengths and transmits it to the WDM line 10, or converts the optical signal from the WDM line 10 into four wavelengths. To divide.

  The switching unit 12 is a layer 2 switch or the like similarly to the switching unit 5. The switching unit 12 is connected to all ports of the input / output I / Fs 4e to 4h according to instructions from the control unit 13. In the present embodiment, the control unit 13 adds the analyzed operation state information of the transmission device 3b to all four overheads and transfers the information to the transmission device 3a by in-band communication. Thereby, even if some trouble occurs, the operating state of the transmission device 3b is reliably transferred to the transmission device 3a. In addition, the switching unit 5 of the transmission device 3a selects one input / output I / F, and the switching unit 12 selects all the input / output I / Fs 4e to 4h, and the Ethernet network between the transmission devices 3a and 3b. Since the in-band communication is established without the loop configuration, packet storms and the like can be avoided in advance.

  The control unit 13 controls the operation of the transmission device 3b, analyzes the operation state of the transmission device 3b, and transfers it to the control unit 7. As the control unit 13, a general CPU or the like can be used similarly to the control unit 7. In the present embodiment, a program in which the control unit 13 controls the transmission device 3b and analyzes an operation state of the transmission device 3b is stored in a memory provided in the control unit 13 or an external memory (not shown). The control unit 13 reads and executes the program when the transmission apparatus 3b is activated.

  Next, FIG. 3 shows the configuration of each of the input / output I / Fs 4 a to 4 h, and includes an O / E conversion unit 41, a field programmable gate array (FPGA) 42, and a PHY unit 43.

  The O / E converter 41 converts an optical signal into an electrical signal or an electrical signal into an optical signal.

  The FPGA 42 is a gate array in which a user can write a unique program. The FPGA 42 in this embodiment receives an Ethernet frame having a command or data from the control unit 7 or 13 via the PHY unit 43, and decomposes it by a predetermined number of bytes (2 bytes in this embodiment). The FPGA 42 writes 2 bytes of the divided Ethernet frame into the area 23 for 2 bytes other than the AU pointer area in the overhead 21 of each frame 20 of the SDH system of the main signal directed to the opposite transmission apparatus 3a or 3b. The frame 20 is transferred to the opposite transmission apparatus 3a or 3b. The FPGA 42 extracts 2 bytes at a time from the area 23 in the overhead 21 of the frame 20 that is the main signal from the opposite transmission apparatus 3a or 3b, and reconstructs one Ethernet frame. The FPGA 42 transmits to the control unit 7 or 13 via the PHY unit 43.

  Further, the FPGA 42 of the transmission device 3b directly receives information on the operation state of the transmission device 3b from the control unit 13 without passing through the PHY unit 43, and overhead of each frame 20 of the main signal directed to the opposite transmission device 3a. 21 is written in the area 24 in the overhead 21 different from the area 23, and the frame 20 is transferred to the transmission apparatus 3a. On the other hand, the FPGA 42 of the transmission apparatus 3a extracts information on the operation state of the transmission apparatus 3b from the area 24 in the overhead 21 of the main signal from the opposite transmission apparatus 3b. The FPGA 42 of the transmission device 3 a directly transmits information on the operation state of the transmission device 3 b to the control unit 7 without going through the PHY unit 43. Therefore, the operation of the FPGA 42 eliminates the need for dedicated use of one of the lines for transferring the main signal in order to perform in-band communication between the transmission apparatuses 3a and 3b.

  The PHY unit 43 adjusts the waveform of the digital signal of the Ethernet frame exchanged between the switching unit 5 or 12 and the FPGA 42.

  Next, operations of the transmission apparatuses 3a and 3b according to the present embodiment in the transmission system of FIG. 1 will be described based on the flowchart of FIG.

  When the user inputs power to the transmission devices 3a and 3b, the control unit 7 reads the control program for the transmission device 3a from the storage device 6, and the control unit 13 reads and executes the control program for the transmission device 3b from the memory (not shown). To do. The control unit 7 performs the operations from step S101 to step S104, and the control unit 13 performs the operation of step S101 at predetermined time intervals (10 milliseconds in this embodiment). In the present embodiment, the control unit 7 performs in-band communication with the transmission device 3b using a line connected to the input / output I / F 4a. That is, the control unit 7 instructs the switching unit 5 to select and switch the input / output I / F 4a.

  Step S101: The control unit 7 acquires information on the operating state of the transmission apparatuses 3a and 3b. For example, the control unit 7 determines whether or not each input / output I / F 4a to 4d is out of order, whether or not the link between the switching unit 5 and each input / output I / F 4a to 4d is normal, or transmission. The operating state of the transmission device 3a, such as whether or not a line disconnection has occurred between the devices 3a and 3b, is examined.

  On the other hand, the control unit 13 analyzes the operation state of the transmission device 3b at a time interval of 10 milliseconds. The control unit 13 transmits information on the operation state of the transmission device 3b to the FPGA 42 of all the input / output I / Fs 4e to 4h. Each of the input / output I / Fs 4e to 4h writes and transfers to the area 24 in the overhead 21 of each frame 20 of the main signal directed to the transmission device 3a via the FPGA 42. The input / output I / Fs 4a to 4d of the transmission device 3a extract information on the operating state of the transmission device 3b from the area 24 of each transferred frame 20, and transmit the information to the control unit 7. The control unit 7 receives information on the operating state of the transmission device 3b. Since the information on the operation state of the transmission device 3b is received by all the input / output I / Fs 4a to 4d, the transmission device 3a can acquire information from any input / output I / F. There is heavy reliability.

  Step S102: The control unit 7 registers and saves information on the operation state of the transmission device 3a and the transmission device 3b in the history database of the storage device 6.

  Step S103: The control unit 7 determines whether or not there is information indicating that a failure has occurred in the operation state information of the transmission apparatuses 3a and 3b obtained in Step S101. If no failure has occurred (NO side), the series of operations is terminated. On the other hand, if a failure has occurred (YES side), the control unit 7 displays the alarm on the monitor of the terminal 2 and proceeds to step S104.

  Here, as a failure assumed to occur in the present embodiment, for example, a link down due to a failure of the input / output I / Fs 4a to 4h, a failure in the forward path or the return path of a line of any wavelength of the WDM line 10, etc. There is a line disconnection.

  Step S104: The control unit 7 determines whether or not the failure found in Step S103 has occurred between the input / output I / Fs 4a and 4e that are performing in-band communication from the transmission device 3a to the transmission device 3b. judge. If no failure has occurred between the input / output I / Fs 4a and 4e (NO side), the series of operations is terminated without switching the line for in-band communication. On the other hand, when a failure occurs between the input / output I / Fs 4a and 4e (YES side), the control unit 7 causes the switching unit 5 to input / output I / Fs 4b to 4d in which no failure has occurred. Instruct to switch to one of the following to avoid the failure. The control unit 7 ends the series of operations. When the next 10 milliseconds have elapsed, the control units 7 and 13 perform the operations from step S101 to step S104 again.

  As described above, in this embodiment, the information on the operation state of the transmission apparatus 3b is written and transferred in a part of the overhead 21 of each frame 20 of the main signal to be transferred, so that a part of the line is used exclusively. Therefore, it is possible to avoid a failure that has occurred in the transmission system.

  Therefore, the user can reliably connect to the transmission apparatus 3a or 3b by in-band communication using the terminal 2, and can perform a recovery operation for the failure that has occurred.

Further, when performing in-band communication between the transmission apparatuses 3a and 3b, the switching unit 5 selects one of the input / output I / Fs 4a to 4d, and the switching unit 12 selects the input / output I / Fs 4e to 4h. Since all are used, it is possible to reliably avoid a failure occurring between the opposing transmission apparatuses 3a and 3b in a short time.
≪Supplementary items for the embodiment≫
In the present embodiment, the pair of transmission systems including the transmission apparatuses 3a and 3b has been described, but the present invention is not limited to this. For example, as shown in FIG. 5, transmission apparatuses 3a and 3b may be connected in multiple stages. In the case of the two-stage connection in FIG. 5, work for avoiding a failure is performed in each of the pair of transmission apparatuses 3a-1 and 3b-1 and transmission apparatuses 3a-2 and 3b-2. The transmission apparatuses 3a-1 and 3a-2 have the same configuration as the transmission apparatus 3a in FIG. 1, and the transmission apparatuses 3b-1 and 3b-2 have the same configuration as the transmission apparatus 3b, respectively. However, since the transmission apparatuses 3b-1 and 3a-2 are directly connected by four optical fiber lines, the main signal is transferred through these lines. Further, since the transmission apparatuses 3b-1 and 3a-2 are also connected by an Ethernet work line, the Ethernet frame for in-band communication is transferred by the Ethernet work line. Note that one end of the Ethernet work line is connected to the switching unit 12 of the transmission device 3b-1, and the other end is connected to the switching unit 5 of the transmission device 3a-2. The control unit 7 and the transmission device of the transmission device 3a-1 It is preferable that the Ethernet frames be transferred to each other based on the instruction of the control unit 13 of 3b-1. Therefore, in the transmission system as shown in FIG. 5, for example, the information on the operation state of the transmission device 3b-2 displayed on the monitor of the terminal 2 is the transmission devices 3b-2 to 3a-2 and the transmission devices 3b-1 to 3a. -1 is transferred by in-band communication via the WDM line 10 and from the transmission apparatuses 3a-2 to 3b-1 via the Ethernet work line.

  In this embodiment, the transmission apparatuses 3a and 3b are connected by the WDM line 10 and the main signal is transferred by the method using wavelength division multiplexing. However, the present invention is not limited to this. The input / output I / Fs 4a to 4d and the input / output I / Fs 4e to 4h may be independently connected by optical fibers.

  In the present embodiment, the transmission apparatuses 3a and 3b are WDM apparatuses connected to the network 1a and the network 1b through four optical fiber lines, respectively. However, the present invention is not limited to this. A WDM device connected by a plurality of optical fiber lines such as 16 can be used.

  In this embodiment, the FPGA 42 divides the Ethernet frame by 2 bytes and writes it in the area 23 of the SDH frame 20 or extracts 2 bytes from the area 23 of the frame 20 to reconstruct the Ethernet frame. However, the present invention is not limited to this. The FPGA 42 may divide the Ethernet frame by an arbitrary number of bytes and write it in an area other than the area 23 of the overhead 21 of the frame 20 or extract it from the overhead 21 of the frame 20 to reconstruct the Ethernet frame.

  In the present embodiment, the FPGA 42 of the transmission apparatus 3b writes the information on the operation state of the transmission apparatus 3b to the area 24 of the SDH frame 20, and the FPGA 42 of the transmission apparatus 3a starts from the area 24 of the frame 20 to the transmission apparatus 3b. However, the present invention is not limited to this. Information on the operating state of the transmission device 3b may be written in an area other than the area 24 of the overhead 21 of the frame 20 or extracted from the overhead 21 of the frame 20.

  In the present embodiment, the operation of the flowchart of FIG. 4 is repeated at intervals of 10 milliseconds, but the present invention is not limited to this. It is preferable to determine according to the processing capability of the control units 7 and 13 and conditions required for the transmission apparatuses 3a and 3b.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

1 is a conceptual diagram of a transmission system according to an embodiment of the present invention. The figure which shows the structure of the flame | frame 20 of a SDH system The figure which shows the structure of input-output I / F4a-4h The flowchart which shows the work procedure of the transmission system which concerns on one Embodiment of this invention. Diagram when the transmission system of FIG. 1 is connected in two stages

Explanation of symbols

1a, 1b network, 2 terminal, 3a, 3b transmission device, 4a to 4h input / output I / F, 5, 12 switching unit, 6 storage device, 7, 13 control unit, 8, 11 multiplexing / division unit, 10 WDM line , 20 frames, 21 overhead, 22 payloads, 23 and 24 areas, 41 O / E converter, 42 FPGA, 43 PHY

Claims (7)

A transmission system comprising two transmission devices connected to each other by a plurality of transmission paths so as to communicate between networks,
The transmission device of one hand is
Network for transferring main signals to the network that is connected to the transmission device of said one from said plurality of transmission line network or al the other to the transmitting device or the other transmission apparatus which is connected to the transmission device of said one via An interface part;
A switching unit that selects one of the plurality of transmission lines and establishes in-band communication with the other transmission device ;
An extraction unit for extracting information of an operation state of the other side transmission apparatus from said main signal from the other transmission apparatus for transferring each of the plurality of transmission paths,
Based on the extracted information of the operating state of the other transmission device and a control unit for monitoring the operation state of the other transmission device,
The other transmission device is
A network that transfers the main signal from the one transmission device to the network connected to the other transmission device or from the network connected to the other transmission device to the one transmission device via the plurality of transmission paths. An interface part;
An analysis unit for examining an operation state of the other transmission device;
An additional unit for transferring information on the operating state of the other transmission device to each of the plurality of transmission lines and adding the information to the one main transmission device ;
The controller is
Based on the operating state of the other transmission device, it is determined whether or not a failure has occurred in the transmission path selected by the switching unit, and operates normally with respect to the switching unit according to the determination result. The in-band communication is performed by switching to the other transmission path . The transmission system according to claim 1, wherein
The adding unit adds information on an operating state of the other transmission device to an overhead of an SDH frame of the main signal going to the one transmission device,
The extraction unit extracts information on an operation state of the other transmission apparatus from an overhead of an SDH frame of the main signal from the other transmission apparatus. In the transmission system according to claim 1 or 2,
Prior Symbol controller, monitors the operation state of the other transmission apparatuses, wherein examining the operation state of one of the transmission device, on the basis of the operating state of the one of the transmission device and the other transmission devices, wherein It is determined whether or not a failure has occurred in the transmission path selected by the switching unit. The transmission system according to any one of claims 1 to 3,
The two transmission apparatuses are wavelength division multiplexing apparatuses. Of the two connected transmission device by a plurality of transmission lines facing each other for communication between networks, a transmission device for receiving information in the operation state of the other of said transmission device,
A network interface unit for transferring main signals from the plurality of via the transmission path or from a network connected to the own device to the other transmission device the other transmission devices to the network connected to the own device,
A switching unit that selects one of the plurality of transmission lines and establishes in-band communication with the other transmission device ;
An extraction unit that extracts information on an operating state of the other transmission device from the main signal from the other transmission device that transfers each of the plurality of transmission lines;
Based on the extracted information of the operating state of the other transmission device and a control unit for monitoring the operation state of the other transmission device,
The controller is
Based on the operating state of the other transmission device, it is determined whether or not a failure has occurred in the transmission path selected by the switching unit, and operates normally with respect to the switching unit according to the determination result. The in-band communication is performed by switching to the other transmission line
Transmission and wherein the this. Among the plurality of transmission paths by the two connected transmission devices face each other for communication between networks, a transmission apparatus which notifies the information of the operating state of the apparatus to one of the transmission device,
The main signal is transferred from the one transmission apparatus to the network connected to the own apparatus or from the network connected to the own apparatus to the one transmission apparatus via the plurality of transmission paths, and the one transmission is performed. A network interface unit for performing in-band communication with the device ;
An analysis unit checks the operation state of the own device,
An adding unit for transferring the information on the operating state of the own device to the main signal that is transferred to each of the plurality of transmission paths and is directed to the one transmission device;
A transmission apparatus comprising: A transmission method in a transmission system composed of two transmission devices connected to each other by a plurality of transmission paths to perform communication between networks,
One of the transmission device, the steps to establish a in-band communication with the other of said transmission device selects one of the transmission lines among the plurality of transmission paths,
The other transmission device checks the operating state of the device ;
The other transmission device transfers information on the operation state of the own device to the main signal that is transferred to each of the plurality of transmission paths and directed to the one transmission device;
The one transmission apparatus extracts information on an operating state of the other transmission apparatus from the main signal from the other transmission apparatus that transfers each of the plurality of transmission paths;
The one transmission device monitoring the operation state of the other transmission device based on the extracted operation state information of the other transmission device;
It said one transmission device, on the basis of the operating state of the other transmission devices, other a fault in the transmission path selected determines whether or not occur, operating normally in accordance with the determination result Switching to the transmission path and performing the in-band communication ;
A transmission method comprising:

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