JP5644226B2 - Redundant pair, signal transmission method and program - Google Patents

Description

  The present invention relates to a redundant pair used as a node of a communication network in which a communication path is made redundant and one signal is transmitted through a plurality of communication paths, a signal transmission method for the redundant pair, and a control program for the transmission device for the redundant pair About.

  One technique for improving the fault tolerance of a communication network is redundancy of communication paths. For example, the SNC (Sub Network Connection Protection) SDH (Synchronous Digital Hierarchy) network shown in Patent Document 1 includes a double ring network, and when a failure occurs in the active ring, the active network Communication is performed using a standby ring that transmits a signal in the opposite direction to the ring.

FIG. 11 is a configuration diagram illustrating a configuration example of an SNC type SDH network. The SDH network 1001 in FIG. 1 includes SDH apparatuses 1300 and 1400 and communication paths W1134, W1143, W1234, and W1243 that connect these SDH apparatuses. In addition, an external device 1600 is connected to the SDH device 1300 via communication paths W1036 and W1063. In addition, an external device 1700 is connected to the SDH device 1400 via communication paths W1047 and W1074.
A ring network is formed by the SDH apparatuses 1300 and 1400 and the communication paths W1143 and W1234. A ring network that transmits signals in the reverse direction of the ring is formed by the SDH devices 1300 and 1400 and the communication paths W1134 and W1243. The SDH network 1001 duplicates a communication signal between the external device 1600 and the external device 1700, and transmits it via these two rings.

FIG. 12 is a configuration diagram illustrating a configuration example of the SDH apparatuses 1300 and 1400 in the network 1001.
The communication signal transmitted from the external apparatus 1600 is transmitted to the external apparatus communication unit 1063 of the SDH apparatus 1300 through the communication path W1063. The signal transmitted from the external device 1600 is, for example, an Ethernet signal (Ethernet is a registered trademark), and the external device communication unit 1063 converts the signal into an SDH signal and outputs the SDH signal to the branch unit 1321. The branching unit 1321 duplicates the SDH signal from the external device communication unit 1063 and outputs it to the opposite device communication units 1311 and 1312. The opposing device communication unit 1311 transmits the SDH signal from the branching unit 1321 to the SDH device 1400 via the communication path W1234. Similarly, the opposing device communication unit 1312 transmits the SDH signal from the branching unit 1321 to the SDH device 1400 via the communication path W1134.

In the SDH device 1400, the opposite device communication unit 1412 receives the SDH signal from the opposite device communication unit 1311 and outputs it to the selector 1431. Similarly, the opposing device communication unit 1411 receives the SDH signal from the opposing device communication unit 1312 and outputs it to the selector 1431.
The selector 1431 selects a signal in which no error is detected from the SDH signal transmitted from the opposite device 1411 and the SDH signal transmitted from the opposite device 1412, and outputs the selected signal to the external communication unit 1413. The external communication device 1413 converts the SDH signal from the selector 1431 into, for example, an Ethernet signal (Ethernet is a registered trademark), and transmits the signal to the external device 1700 through the communication path W1047.
When the signal from the external device 1700 is transmitted to the external device 1600, the signal is duplicated by the branching unit 1421 and transmitted through the communication paths W1143 and W1243, and the selector 1331 selects a signal in which no error is detected, and the external device communication unit 1313 transmits to the external device 1600.

  As described above, the SDH network 1001 realizes a protection function by duplicating a signal to be transmitted and transmitting the signal through two rings. As a result, the transmission service can be continued even if a failure occurs in any of the opposing device communication units 1311, 1312, 1411, 1412 or any of the communication paths W1134, W1143, W1234, and W1243.

Japanese Patent Laid-Open No. 9-233083

  However, in this system, when a failure occurs in the communication path between the SDH apparatus or the SDH apparatus and the external apparatus, the transmission service cannot be continued. Specifically, in the SDH network 1001 of FIG. 12, when a failure occurs in the external device 1313 or 1413, the branching device 1321 or 1421, or the selector 1331 or 1431, or the communication paths W1036, W1063, W1047, and W1074. If a failure occurs in any of the above, the transmission service cannot be continued.

  The present invention has been made in view of such circumstances, and its purpose is to transmit even when a failure occurs in a transmission device (SDH device) or a communication path between the transmission device and an external device. It is to provide a redundant pair, a signal transmission method and a program that can provide a service.

The present invention has been made to solve the above-described problem, and a redundant pair according to an aspect of the present invention is a redundant pair including a main transmission device and an alternative transmission device, and the main transmission device is A first counter device communication unit, a first redundant pair communication unit, a first external device communication unit, and a main transmission device state determination unit that determines the state of the main transmission device to be either an execution state or a standby state. The alternative transmission device includes a second opposing device communication unit, a second redundant pair communication unit, a second external device communication unit, and the main transmission device state determination unit that determines the state of the main transmission device. When the execution state is determined, the state of the alternative transmission device is determined as a standby state, and when the main transmission device state determination unit determines the state of the main transmission device as a standby state, the state of the alternative transmission device is determined as an execution state. An alternative transmission device state determination unit; The first counter device communication unit and the second counter device communication unit send the same signal obtained by duplicating a signal addressed to an external device to the first counter device communication unit and the second counter device communication unit. The first redundant pair communication unit can communicate with the transmitting opposite device to transmit, and when the main transmission device state determination unit determines the state of the main transmission device as a standby state, the first opposite device communication unit The same signal to be received is transmitted to the second redundant pair communication unit, and the second redundant pair communication unit, when the alternative transmission device state determination unit determines the state of the alternative transmission device as a standby state, 2 The same signal received by the opposite device communication unit is transmitted to the first redundant pair communication unit, and the first external device communication unit executes the state of the main transmission device by the main transmission device state determination unit. Is determined, the first opposing device communication unit Of the same signal to be transmitted and the same signal received by the first redundant pair communication unit is transmitted to the external device, the second external device communication unit, When the alternative transmission device state determination unit determines the state of the alternative transmission device as an execution state, the same signal received by the second counter device communication unit and the same signal received by the second redundant pair communication unit Of the signals, a signal for which no error is detected is transmitted to the external device.

  A signal transmission method according to an aspect of the present invention is a redundant pair signal transmission method including a main transmission device and an alternative transmission device, and the main transmission device executes a state of the main transmission device. A main transmission device state determination step for determining either a state or a standby state; and when the alternative transmission device determines the state of the main transmission device as an execution state in the main transmission device state determination step, the alternative transmission device An alternative transmission device state determination step for determining a state as a standby state, and determining the state of the alternative transmission device as an execution state when the main transmission device state is determined as a standby state in the main transmission device state determination step; A first reception step in which the same signal obtained by duplicating the signal addressed to the device is transmitted from the opposite device and received by the main transmission device and the alternative transmission device; A first transmission step of transmitting the same signal received in the first reception step to the alternative transmission device when the state of the main transmission device is determined as a standby state in the main transmission device state determination step; When the transmission apparatus determines the state of the alternative transmission apparatus as a standby state in the alternative transmission apparatus state determination step, the second transmission that transmits the same signal received in the first reception step to the main transmission apparatus And when the main transmission apparatus determines that the state of the main transmission apparatus is an execution state in the main transmission apparatus state determination step, the same signal received in the first reception step, and the second transmission A third transmission step of transmitting, to the external device, a signal from which no error is detected among the same signals transmitted from the alternative transmission device in the step; When the replacement transmission apparatus determines the state of the alternative transmission apparatus as an execution state in the alternative transmission apparatus state determination step, the same signal received in the first reception step and the first transmission step And a fourth transmission step of transmitting, to the external device, a signal from which an error is not detected among the same signals transmitted from the alternative transmission device.

In addition, a program according to one embodiment of the present invention can execute a state of a transmission device on a computer as a control unit of the transmission device including an opposing device communication unit, a redundant pair communication unit, and an external device communication unit. When the state determination step to determine one of the standby states and the execution state at the state determination step, when the execution state is determined, select the signal received by the external device communication unit as a signal transmitted by the opposing device communication unit, When the standby state is determined in the state determination step, a first signal selection step of selecting a signal received by the redundant pair communication unit as a signal transmitted by the opposing device communication unit, and the state determination step when it is determined that execution state selects a signal in which the redundant pair communication unit is received by the external device communication portion as a signal to be transmitted, waiting at the state determination step When state determination is a program for the redundant pair communication unit to execute the second signal selection step of selecting the signal received by the opposite device communication unit as a signal to be transmitted.

  According to the present invention, it is possible to provide a transmission service even when a failure occurs in a transmission device or a communication path between the transmission device and an external device.

It is a block diagram which shows schematic structure of the SDH network in one Embodiment of this invention. In the embodiment, the SDH network 1 is a configuration diagram showing a schematic configuration example including one redundant pair and two SDH devices. It is a block diagram which shows schematic structure of the duplex SDH apparatus 100 in the embodiment. It is a block diagram which shows schematic structure of the SDH apparatus 300 in the embodiment. 4 is a diagram illustrating a path of a signal transmitted from the external apparatus 700 to the external apparatus 600 when the duplexed SDH apparatus 100 is in an execution state in the embodiment. FIG. 5 is a diagram illustrating a path of a signal transmitted from the external device 600 to the external device 700 when the duplexed SDH device 100 is in an execution state in the embodiment. FIG. 5 is a diagram illustrating a flow of failure information when a failure occurs in an external device communication unit 113 in the embodiment. FIG. 5 is a diagram illustrating a flow of control information (status information) when a failure occurs in an external device communication unit 113 in the embodiment. FIG. 5 is a diagram illustrating a path of a signal transmitted from the external apparatus 700 to the external apparatus 600 when the duplexed SDH apparatus 200 is in an execution state in the embodiment. FIG. 5 is a diagram illustrating a path of a signal transmitted from the external device 600 to the external device 700 when the duplexed SDH device 200 is in an execution state in the embodiment. FIG. 1 is a configuration diagram illustrating a configuration example of an SNC type SDH network. FIG. 2 is a configuration diagram illustrating a configuration example of SDH apparatuses 1300 and 1400 in a network 1001. FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram showing a schematic configuration of an SDH network in an embodiment of the present invention. In FIG. 1, an SDH network 1 connects a duplexed SDH apparatus (main transmission apparatus) 100, a duplexed SDH apparatus (alternate transmission apparatus) 200, an SDH apparatus (opposite apparatus) 300, and duplexed SDH apparatuses 100 and 200. Communication paths W12 and W21, communication paths W13 and W31 connecting the duplexed SDH apparatus 100 and the SDH apparatus 300, and communication paths W23 and W32 connecting the duplexed SDH apparatus 200 and the SDH apparatus 300 are provided.

The redundant SDH apparatuses 100 and 200 form a redundant pair 10 and function as one node of the SDH network 1. One of the duplexed SDH apparatuses 100 and 200 configuring the redundant pair is in an execution state (act, ACT), and communicates with the external apparatus 600. The other is in a standby state (standby, STB) and transmits a signal from the duplexed SDH device in the running state to the SDH device 300, and transmits a signal from the SDH device 300 to the duplexed SDH device in the running state. Perform transmission. When a failure occurs in the duplexed SDH device in the execution state, the duplexed SDH device in the execution state enters the standby state, and the duplexed SDH device in the standby state enters the execution state and continues signal transmission.
On the other hand, the SDH apparatus 100 is a general SDH apparatus, and one unit functions as one node of the SDH network.

The duplexed SDH apparatuses 100 and 200 are connected to an external apparatus 600 via communication paths W16 and W61 and communication paths W26 and W62, respectively. In addition, an external device 700 is connected to the SDH apparatus 300 via communication paths W37 and W73.
The redundant pair 10 and the external device 600, and the SDH device 300 and the external device 700 are respectively connected by Ethernet (registered trademark), and the SDH network 1 provides an Ethernet transmission service (for the external devices 600 and 700). Ethernet provides a registered trademark).

  The duplex SDH apparatuses 100 and 200, the SDH apparatus 300, and the communication paths W12, W23, and W31 form a ring network. Then, a ring network that transmits signals in the reverse direction of the ring is formed by the duplex SDH devices 100 and 200, the SDH device 300, and the communication paths W21, W13, and W32. The SDH network 1 realizes a protection (switching) function by duplicating a communication signal between the external apparatus 600 and the external apparatus 700 and transmitting the duplicated signal through these two rings.

  Note that the number of redundant pairs constituting the network as nodes of the SDH network 1 is not limited to one set shown in FIG. 1 and may be two or more sets. Further, the number of SDH apparatuses constituting the network as the nodes of the SDH network 1 is not limited to one as shown in FIG. 1, but two or more nodes are used so that the SDH network 1 functions as a network, that is, a redundant pair and an SDH. Two or more devices may be used together with the device. For example, the SDH network 1 may include a redundant pair instead of the SDH apparatus 300 of FIG. Alternatively, as illustrated in FIG. 2, the SDH network 1 may further include one SDH device from the configuration illustrated in FIG. 1.

  FIG. 2 is a configuration diagram illustrating a schematic configuration example in which the SDH network 1 includes one redundant pair and two SDH devices. In the figure, the duplex SDH devices 100 and 200, the SDH devices 300 and 400, and the communication paths W12, W24, W43, and W31 form a ring network. A ring network that transmits signals in the reverse direction of the ring is formed by duplexed SDH devices 100 and 200, SDH devices 300 and 400, and communication paths W21, W13, W34, and W42. The SDH network 1 realizes a protection function by duplicating a communication signal between the external devices 600, 700, and 800 and transmitting the duplicated signal through these two rings.

  For example, when a communication signal from the external device 800 is transmitted to the external device 600 through the duplexed SDH device 100, the SDH device 400 duplicates the communication signal from the external device 800, and the communication path W43, the SDH apparatus 300, and the communication path W31. The communication signal is transmitted through both of the transmission path in the order of the duplexed SDH apparatus 100 and the path of transmission from the SDH apparatus 400 in the order of the communication path W42, the duplexed SDH apparatus 200, the communication path W21, and the duplexed SDH apparatus 100.

Next, the internal configuration of the duplexed SDH apparatus 100 will be described with reference to FIG.
FIG. 3 is a configuration diagram illustrating a schematic configuration of the duplexed SDH apparatus 100. The duplexed SDH apparatus 100 includes a counter device communication unit (first counter device communication unit) 111, a redundant pair communication unit (first redundant pair communication unit) 112, an external device communication unit (first external device communication unit) 113, and Branching devices 121 and 122 and 123, selectors 131 and 132 and 133, an overhead (OH) monitoring unit 161, an overhead insertion unit 162, a failure information generation unit (main transmission apparatus failure information generation unit) 171 , A failure information communication unit (first failure information communication unit) 172, and a state determination unit (main transmission device state determination unit) 173. The external device communication unit 113 includes a transmission / reception unit 117, an Ethernet terminator 116 (Ethernet is a registered trademark), a VCAT terminator 115, and a VC path terminator 114.

The external device communication unit 113 communicates with an external device. In the present embodiment, the external device communication unit 113 is connected to the external device 600 via Ethernet (registered trademark) to perform communication.
The transmission / reception unit 117 receives a signal from an external device and outputs it to the Ethernet terminator 116 (Ethernet is a registered trademark). The transmission / reception unit 117 transmits a signal output from the Ethernet terminator 116 (Ethernet is a registered trademark) to an external device.
The Ethernet terminator 116 (Ethernet is a registered trademark) terminates an Ethernet signal (Ethernet is a registered trademark) transmitted from an external device, and outputs the terminated signal to the VCAT terminator 115. The Ethernet terminator 116 (Ethernet is a registered trademark) converts the signal output from the VCAT terminator 115 into an Ethernet signal (Ethernet is a registered trademark) and outputs the Ethernet signal to the transmission / reception unit 117.

The VCAT terminator 115 maps the signal output from the Ethernet terminator 116 (Ethernet is a registered trademark) to the VCAT signal and outputs the signal to the VC path terminator 114. The VCAT terminator 115 demaps the VCAT signal output from the VC path terminator 114 and outputs it to the Ethernet terminator 116 (Ethernet is a registered trademark).
The VC path terminator 114 maps the VCAT signal output from the VCAT terminator 115 to the VC path constituting the VCAT, generates an SDH signal, and outputs the generated SDH signal to the branching device 123. Further, the VC path terminator 114 demaps the SDH signal output from the selector 133 and outputs the obtained VCAT signal to the VCAT terminator 115.
As described later, the external device communication unit 113 shuts down and does not communicate with the external device 600 when the duplexed SDH device 100 is in a standby state. On the other hand, when the duplexed SDH apparatus 100 enters an execution state, the external apparatus communication unit 113 is activated and can communicate with the external apparatus 600.

  The opposing device communication unit 111 performs communication with the opposing device. That is, the opposing device communication unit 111 transmits the SDH signal output from the selector 131 to the opposing device, and outputs the SDH signal transmitted from the opposing device to the branching device 121. Here, the opposite device is an SDH device or a duplexed SDH device to which an external device that is a communication partner of the external device connected to the duplexed SDH device 100 is connected. For example, in FIG. 1, the opposite device of the duplexed SDH device 100 is the SDH device 300. In FIG. 2, when the external device 600 is communicating with the external device 700, the opposite device of the duplexed SDH device 100 is the SDH device 300. On the other hand, in FIG. 2, when the external device 600 is communicating with the external device 800, the opposite device of the duplexed SDH device 100 is the SDH device 400.

  The redundant pair communication unit 112 performs communication between the duplexed SDH apparatus 100 and the duplexed SDH apparatus 200 configuring the redundant pair 10. That is, the redundant pair communication unit 112 transmits the SDH signal into which the failure information is inserted, which is output from the overhead insertion unit 162, to the duplexed SDH device 200, and the SDH signal (duplexed) transmitted from the duplexed SDH device 200. SDH signal in which failure information of the SDH apparatus 200 is inserted into the overhead portion) is output to the overhead monitoring unit 161.

  The branching device 121 outputs the SDH signal output from the opposite device communication unit 111 to the selector 133 and the selector 132. The branching device 122 outputs the SDH signal output from the overhead monitoring unit 161 to the selector 131 and the selector 133. The branching device 123 outputs the SDH signal output from the VC path terminator 114 to the selectors 131 and 132.

Based on the state of the duplexed SDH device 100 determined by the state determining unit 173, the selector 131 outputs the SDH signal from the branching device 123 to the opposite device communication unit 111 when the duplexed SDH device 100 is in the execution state. . On the other hand, when the duplexed SDH device 100 is in the standby state, the selector 131 outputs the SDH signal from the branching device 122 to the opposite device communication unit 111.
Thereby, when the duplexed SDH apparatus 100 is in the execution state, the selector 131 transmits the signal received from the external apparatus to the opposite apparatus, and when the duplexed SDH apparatus 100 is in the standby state. Transmits a signal received from an external device to another device by another duplexed SDH device (duplexed SDH device 200 in the present embodiment) constituting a redundant pair.

The selector 132 outputs the SDH signal from the branching device 123 to the overhead inserting unit 162 when the duplexed SDH device 100 is in the execution state based on the state of the duplexed SDH device 100 determined by the state determining unit 173. On the other hand, when the duplexed SDH apparatus 100 is in the standby state, the selector 132 outputs the SDH signal from the branching device 121 to the overhead insertion unit 162.
As a result, when the duplexed SDH device 100 is in the execution state, the selector 132 transmits the signal received from the external device to the other duplexed SDH devices that form the redundant pair, and the duplexed SDH device 100 is duplexed. When the SDH apparatus 100 is in a standby state, the signal received from the opposite apparatus is transmitted toward another duplexed SDH apparatus that forms a redundant pair.
As will be described later, the duplexed SDH device 100 communicates with the external device when the duplexed SDH device 100 is in the running state by selecting the signals of the selector 131 and the selector 132, and is in a standby state. In the case of (2), a communication signal is transmitted between the other duplexed SDH apparatus and the opposite apparatus constituting the redundant pair.
Further, the selector 133 performs an error check on the SDH signal from the branching device 121 and the SDH signal from the branching device 122, and outputs one of the SDH signals that does not detect an error to the VC path terminator 114. .

The failure information generation unit 171 monitors the presence / absence of failures in the external device communication unit 113, the branching device 123, and the selector 133 as needed. The external device communication unit 113, the branching device 123, and the selector 133 are portions that handle signals that are not duplicated, and if a failure occurs in any of them, a transmission service cannot be provided to the external device. There is a risk that. Therefore, the failure information generation unit 171 monitors the presence or absence of these failures.
Furthermore, the failure information generation unit 171 monitors the presence or absence of a failure in the communication path between the external device communication unit 113 and the external device 600 as needed. For example, a signal is periodically transmitted from the external device communication unit 113 to the external device 600, and the failure information generation unit 171 determines the presence or absence of a failure in the communication path based on the presence or absence of a reply from the external device 600.
Then, the failure information generation unit 171 generates failure information indicating the presence or absence of a failure, and outputs the failure information to the failure information communication unit 172, the state determination unit 173, and the overhead insertion unit 162.
Note that the failure information generation unit 171 may also monitor the presence or absence of a failure in another part. For example, when a failure occurs in the branching device 122, it is not immediately possible to provide a transmission service to the external device. However, by detecting this failure and setting the duplexed SDH device 100 in a standby state, the duplexed SDH device 100 is provided. Can be repaired or replaced more smoothly.

The failure information communication unit 172 transmits the failure information output from the failure information generation unit 171 to the duplexed SDH device 200 (the partner that forms the redundant pair 10 with the duplexed SDH device 100).
The state determination unit 173 acquires the failure information of the duplexed SDH device 100 from the failure information generation unit 171 and acquires the failure information of the duplexed SDH device 200 from the failure information communication unit 172 and the overhead monitoring unit 161. . Here, the failure information acquired by the state determination unit 173 from the failure information communication unit 172 and the failure information acquired from the overhead monitoring unit 161 are the same failure information transmitted twice.
Then, the state determination unit 173 determines the state of the duplexed SDH device 100 based on the predetermined ACT priority information, the failure information of the duplexed SDH device 100, and the failure information of the duplexed SDH device 200, as an execution state. Alternatively, it is determined to be in a standby state. Here, the ACT priority information is information indicating which of the redundant pairs is preferentially set to the execution state.

For example, when it is set by the ACT priority information that the duplexed SDH apparatus 100 is preferentially put into the execution state, the state determination unit 173 determines that the duplexed SDH apparatuses 100 and 200 are duplexed when no failure has occurred. The SDH apparatus 100 is put into an execution state (therefore, the duplexed SDH apparatus 200 is set in a standby state).
On the other hand, when a failure has occurred in one of the duplexed SDH devices 100 and 200, the state determination unit 173 sets the duplexed SDH device in which no failure has occurred to the execution state and the other to the standby state.
In the duplexed SDH apparatus 200, the state determination unit 273 similarly determines the state so that one of the duplexed SDH apparatuses 100 and 200 is in the execution state and the other is in the standby state. Alternatively, the state determined by the duplexed SDH apparatus 100 may be transmitted to the duplexed SDH apparatus 200.

  Then, the state determination unit 173 generates state information indicating the determined state, and outputs the state information to the selectors 131 and 132, the overhead insertion unit 162, and the external device communication unit 113.

The overhead insertion unit 162 inserts the failure information (including communication channel failure information; the same applies hereinafter) of the duplexed SDH device 100 output from the failure information generation unit 171 into the overhead portion of the SDH signal output from the selector 132. Then, the SDH signal into which the failure information is inserted is output to the redundant pair communication unit 112.
The overhead monitoring unit 161 outputs the SDH signal output from the redundant pair communication unit 112 to the branching device 122. Further, the overhead monitoring unit 161 reads the status information of the duplexed SDH apparatus 200 from the overhead portion of the SDH signal and outputs it to the status determining unit 173.
Note that the configuration of the duplexed SDH apparatus 200 is the same as that of the duplexed SDH apparatus 100, and a description thereof will be omitted.
In the duplexed SDH apparatus 200, the opposing device communication unit 211 corresponds to the second opposing device communication unit, the redundant pair communication unit 211 corresponds to the second redundant pair communication unit, and the external device communication unit 213 corresponds to the second external device. Corresponding to the communication unit, the failure information generating unit 271 corresponds to the alternative transmission device failure information generating unit, the failure information communication unit 272 corresponds to the second failure information communication unit, and the state determining unit 273 is the alternative transmission device state determining unit. It corresponds to.

Next, an internal configuration of the SDH apparatus 300 will be described with reference to FIG.
FIG. 4 is a configuration diagram illustrating a schematic configuration of the SDH apparatus 300.
The SDH apparatus 300 includes opposing device communication units 311 and 312, an external device communication unit 313, a branching device 321, and a selector 331. The external device communication unit 313 includes a transmission / reception unit 317, an Ethernet terminator 316 (Ethernet is a registered trademark), a VCAT terminator 315, and a VC path terminator 314.
The external device communication unit 313 performs communication with an external device. The transmission / reception unit 317, the Ethernet terminator 316 (Ethernet is a registered trademark), the VCAT termination unit 315, and the VC path termination unit 314 are respectively the transmission / reception unit 117 and the Ethernet termination unit 116 (Ethernet is a registered trademark) in FIG. ), The VCAT terminator 115 and the VC path terminator 114, and the description thereof will be omitted.
The branching device 321 outputs the SDH signal output from the VC path terminator 314 to the opposing device communication units 311 and 312. The opposing device communication units 311 and 312 transmit the same SDH signal output from the branching unit 321 to the same opposing device. That is, the branching device 321, the opposing device communication unit 311, and the opposing device communication unit 312 duplex the SDH signal output from the external device communication unit 313 and transmit it to the opposing device.
The selector 331 performs an error check on the SDH signal from the opposite device communication unit 311 and the SDH signal from the opposite device communication unit 312, and the SDH signal that does not detect any error is sent to the VC path terminator 314. Output.

Next, with reference to FIG. 5 and FIG. 6, the path of the communication signal when the duplexed SDH apparatus 100 is in the execution state (therefore, the duplexed SDH apparatus 200 is in the standby state) will be described.
FIG. 5 is a diagram illustrating a path of a signal transmitted from the external apparatus 700 to the external apparatus 600 when the duplexed SDH apparatus 100 is in an execution state.
When a signal addressed to the external device 600 is transmitted from the external device 700, the external device communication unit 313 receives the signal and outputs it to the branching device 321. The branching device 321 duplicates the signal from the external device communication unit 313 and outputs it to the opposing device communication units 311 and 312, and the opposing devices 311 and 312 respectively send the signal from the branching device 321 to the duplexed SDH device 100. It transmits to the duplex SDH apparatus 200.
The signal transmitted from the opposing device communication unit 311 is received by the opposing device communication unit 111 and output to the branching device 121. The branching device 121 outputs a signal from the opposing device communication unit 111 to the selector 133 (and the selector 132).

On the other hand, the signal transmitted from the opposite device communication unit 312 is received by the opposite device communication unit 211 and transmitted in the order of the branching unit 221 and the selector 232. Here, since duplexed SDH apparatus 200 is in a standby state, selector 232 outputs a signal from branching unit 221 to overhead insertion unit 262. The overhead insertion unit 262 outputs the signal from the selector 232 to the redundant pair communication unit 212, and the redundant pair communication unit 212 transmits the signal to the duplexed SDH device 100.
A signal transmitted from the redundant pair communication unit 212 is received by the redundant pair communication unit 112 and transmitted in the order of the overhead monitoring unit 161, the branching device 122, and the selector 133.
The selector 133 performs an error check on the SDH signal from the branching device 121 and the SDH signal from the branching device 122, and outputs the SDH signal that does not detect any error to the external device communication unit 113. The external device communication unit 113 transmits the signal from the selector 133 to the external device 600.

As described above, the signal transmitted from the external device 700 is transmitted in the order of the SDH device 300, the communication channel W31, and the duplexed SDH device 100, the SDH device 300, the communication channel W32, the duplexed SDH device 200, and the communication channel W21. And the duplexed SDH apparatus 100 in order of transmission in the order of transmission.
The SDH apparatus 300, the communication path W31, and the duplexed SDH apparatus 100 are transmitted in this order in the duplexed SDH apparatuses 100 and 200, the SDH apparatus 300, and the communication paths W12, W23, and W31 described in FIG. It forms part of the ring network that forms. Further, the routes transmitted in the order of the SDH device 300, the communication channel W32, the duplexed SDH device 200, the communication channel W21, and the duplexed SDH device 100 are the duplexed SDH devices 100 and 200 and the SDH device 300 described in FIG. , Forming part of a ring network formed by communication paths W21, W13 and W32.
That is, the SDH network 1 realizes a protection function by duplicating a communication signal between the external device 600 and the external device 700 and transmitting the duplicated signal through these two rings.

FIG. 6 is a diagram illustrating a path of a signal transmitted from the external apparatus 600 to the external apparatus 700 when the duplexed SDH apparatus 100 is in the execution state.
When a signal addressed to the external device 700 is transmitted from the external device 600, the external device communication unit 113 receives the signal and outputs it to the branching device 123. The branching device 123 duplicates the signal from the external device communication unit 113 and outputs it to the selector 131 and the selector 132.
Here, since the duplexed SDH device 100 is in the execution state, the selector 131 outputs the signal from the branching unit 123 to the opposing device communication unit 111. The opposing device communication unit 111 transmits the signal from the selector 131 to the SDH device 300.
The signal transmitted from the opposite device communication unit 111 is received by the opposite device communication unit 311 and output to the selector 331.

Further, since the duplexed SDH apparatus 100 is in the execution state, the selector 132 outputs the signal from the branching unit 123 to the overhead inserting unit 162. The overhead insertion unit 162 outputs the signal from the selector 132 to the redundant pair communication unit 112, and the redundant pair communication unit 112 transmits the signal to the duplexed SDH device 200.
The signal transmitted from the redundant pair communication unit 112 is received by the redundant pair communication unit 212 and transmitted in the order of the overhead monitoring unit 261, the branching device 222, and the selector 231. Here, since the duplexed SDH apparatus 200 is in a standby state, the selector 231 outputs a signal from the branching device 222 to the opposing device communication unit 211. The opposing device communication unit 211 transmits the signal from the selector 231 to the SDH device 300.
The signal transmitted from the opposing device communication unit 211 is received by the opposing device communication unit 312 and output to the selector 331.
The selector 331 performs an error check on the signal from the opposite device communication unit 311 and the signal from the opposite device communication unit 312, and outputs a signal that does not detect any error to the external device communication unit 313. The external device communication unit 313 transmits the signal from the selector 331 to the external device 700.

As described above, the signal transmitted from the external apparatus 600 is transmitted in the order of the duplexed SDH apparatus 100, the communication path W13, and the SDH apparatus 300, the duplexed SDH apparatus 100, the communication path W12, the duplexed SDH apparatus 200, and the communication path. W23 and the SDH device 300 are transmitted in this order, and are transmitted twice.
The duplex SDH apparatus 100, the communication path W13, and the SDH apparatus 300 are transmitted in this order in the duplex SDH apparatuses 100 and 200, the SDH apparatus 300, and the communication paths W21, W13, and W32 described with reference to FIG. It forms part of the ring network that forms. The paths transmitted in the order of the duplexed SDH apparatus 100, the communication path W12, the duplexed SDH apparatus 200, the communication path W23, and the SDH apparatus 300 are the duplexed SDH apparatuses 100 and 200, the SDH apparatus 300 described in FIG. It forms part of a ring network formed by communication paths W12, W23 and W31.
That is, the SDH network 1 realizes a protection function by duplicating a communication signal between the external device 600 and the external device 700 and transmitting the duplicated signal through these two rings.

Next, the flow of failure information and control information when a failure occurs in the duplexed SDH apparatus 100 will be described with reference to FIGS. Note that FIGS. 7 and 8 are separate drawings for easy understanding of the drawings, and do not indicate a temporal order. That is, a part of the information shown in FIG. 8 may be output before or simultaneously with a part of the information shown in FIG.
FIG. 7 is a diagram illustrating a flow of failure information when a failure occurs in the external device communication unit 113.
The failure information generation unit 171 monitors the presence / absence of a failure in the external device communication unit 113 as needed. When a failure is detected in the external device communication unit 113, the failure information generation unit 171 generates failure information indicating the occurrence of the failure, And output to the failure information communication unit 172 and the overhead insertion unit 162.
The failure information communication unit 172 transmits the failure information from the failure information generation unit 171 to the duplexed SDH apparatus 200. The failure information transmitted from the failure information communication unit 172 is received by the failure information communication unit 272 and transmitted to the state determination unit 273.
Further, the overhead insertion unit 162 inserts the failure information from the failure information generation unit 171 into the overhead portion of the SDH signal from the selector 132 and outputs it to the redundant pair communication unit 112. The redundant pair communication unit 112 transmits the SDH signal in which the failure information is inserted from the overhead insertion unit 162 to the duplexed SDH device 200.
The SDH signal transmitted from the redundant pair communication unit 112 is received by the redundant pair communication unit 212 and output to the overhead monitoring unit 261. The overhead monitoring unit 261 reads the status information of the duplexed SDH apparatus 100 from the overhead part of the SDH signal from the redundant pair communication unit 212 and outputs the status information to the status determination unit 273.
As described above, the state determination unit 273 acquires the failure information generated by the failure information generation unit 171 in a double manner through two paths. Thereby, even when failure information cannot be acquired from one route, the state determination unit 273 can acquire failure information from the other route and determine the state of the duplexed SDH device 200.

FIG. 8 is a diagram illustrating a flow of control information (status information) when a failure occurs in the external device communication unit 113.
First, looking at the duplex SDH device 100, the state determination unit 173, and ACT priority information set in advance, and fault information of the duplex SDH device 100 the failure information generating unit 171 generates, fault information generating unit 271 generates The state of the duplexed SDH apparatus 100 is determined based on the failure information of the duplexed SDH apparatus 200 to be performed. Here, since a failure has occurred in the duplexed SDH apparatus 100 and no failure has occurred in the duplexed SDH apparatus 200, the state of the duplexed SDH apparatus 100 is determined as a standby state regardless of the ACT priority information. Then, the state determination unit 173 generates state information indicating the determined state, and outputs the state information to the selectors 131 and 132 and the external device communication unit 113.

The selector 131 selects the SDH signal to be output to the opposing device communication unit 111 based on this state information. Thus, when the duplexed SDH apparatus 100 is in the execution state, the selector 131 transmits a signal received from the external apparatus 600 to the SDH apparatus 300 that is the opposite apparatus, and the selector 131 in the state of FIG. As described above, when the duplexed SDH device 100 is in the standby state, a signal received by the duplexed SDH device 100 from the external device 600 via the duplexed SDH device 200 is transmitted to the opposite device 300.
Similarly, the selector 132 selects the SDH signal to be output to the overhead insertion unit 162 based on the state information from the state determination unit 173. Thereby, when the duplexed SDH apparatus 100 is in the execution state, the selector 132 transmits the signal received from the external apparatus 600 to the duplexed SDH apparatus 200, as shown in FIG. When the duplexed SDH apparatus 100 is in a standby state, the duplexed SDH apparatus 100 transmits a signal received from the SDH apparatus 300 that is the opposite apparatus to the duplexed SDH apparatus 200.
The state information indicating that the duplexed SDH apparatus 100 is in the standby state acts as a shutdown command to the external device communication unit 113, and the external device communication unit 113 is shut down in response to this state signal. The term “shutdown” as used here means that communication with the external device 600 is not performed.

Turning now duplexing SDH device 200, the state determination unit 273, and ACT priority information set in advance, and fault information of the duplex SDH device 100 the failure information generating unit 171 generates, fault information generating unit 271 Based on the generated failure information of the duplexed SDH apparatus 200, the state of the duplexed SDH apparatus 100 is determined. Here, since a failure has occurred in the duplexed SDH device 100 and no failure has occurred in the duplexed SDH device 200, the state of the duplexed SDH device 200 is determined as a standby state regardless of the ACT priority information. Then, the state determination unit 273 generates state information indicating the determined state, and outputs the state information to the selectors 231 and 232 and the external device communication unit 213.

The selector 231 selects an SDH signal to be output to the opposing device communication unit 211 based on this state information. As a result, when the duplexed SDH device 200 is in the execution state as shown in FIG. 8, the selector 231 sends a signal received by the duplexed SDH device 200 from the external device 600 to the SDH device 300 that is the opposite device. On the other hand, when the duplexed SDH device 200 is in a standby state, a signal received by the duplexed SDH device 200 from the external device 600 via the duplexed SDH device 100 is transmitted to the opposite device 300.
Similarly, the selector 232 selects an SDH signal to be output to the overhead insertion unit 262 based on the state information from the state determination unit 273. As a result, when the duplexed SDH apparatus 200 is in the execution state as shown in FIG. 8, the selector 232 transmits the signal received by the duplexed SDH apparatus 200 from the external apparatus 600 to the duplexed SDH apparatus 100, On the other hand, when the duplexed SDH apparatus 200 is in a standby state, the duplexed SDH apparatus 200 transmits a signal received from the SDH apparatus 300 that is the opposite apparatus to the duplexed SDH apparatus 100.
Further, the status information indicating that the duplexed SDH device 200 is in an execution state acts as an activation command to the external device communication unit 213, and the external device communication unit 213 is activated in response to this status signal and externally Communication with the apparatus 600 becomes possible.

Next, with reference to FIG. 9 and FIG. 10, the path of the communication signal when the duplexed SDH apparatus 200 is in the execution state (the duplexed SDH apparatus 100 is in the standby state) will be described.
FIG. 9 is a diagram illustrating a path of a signal transmitted from the external apparatus 700 to the external apparatus 600 when the duplexed SDH apparatus 200 is in an execution state.
When a signal addressed to the external device 600 is transmitted from the external device 700, the external device communication unit 313 receives the signal and outputs it to the branching device 321. The branching device 321 duplicates the signal from the external device communication unit 313 and outputs it to the opposing device communication units 311 and 312, and the opposing devices 311 and 312 respectively send the signal from the branching device 321 to the duplexed SDH device 100. It transmits to the duplex SDH apparatus 200.
The signal transmitted from the opposite device communication unit 312 is received by the opposite device communication unit 211 and output to the branching unit 221. The branching device 221 outputs a signal from the opposing device communication unit 211 to the selector 233 (and the selector 232).

On the other hand, the signal transmitted from the opposite device communication unit 311 is received by the opposite device communication unit 111 and transmitted in the order of the branching device 121 and the selector 132. Here, since duplexed SDH apparatus 100 is in a standby state, selector 132 outputs the signal from branching device 121 to overhead insertion unit 162. The overhead insertion unit 162 outputs the signal from the selector 132 to the redundant pair communication unit 112, and the redundant pair communication unit 112 transmits the signal to the duplexed SDH device 200.
A signal transmitted from the redundant pair communication unit 112 is received by the redundant pair communication unit 212 and transmitted in the order of the overhead monitoring unit 261, the branching device 222, and the selector 233.
The selector 233 performs an error check on the SDH signal from the branching unit 221 and the SDH signal from the branching unit 222 and outputs an SDH signal that does not detect any error to the external device communication unit 213. The external device communication unit 213 transmits a signal from the selector 233 to the external device 600.

As described above, the signal transmitted from the external device 700 is transmitted in the order of the SDH device 300, the communication channel W32, and the duplexed SDH device 200, the SDH device 300, the communication channel W31, the duplexed SDH device 100, and the communication channel W12. And the duplexed SDH device 200 are transmitted in the order of the routes.
The SDH apparatus 300, the communication path W32, and the duplexed SDH apparatus 200 are transmitted in this order in the duplexed SDH apparatuses 100 and 200, the SDH apparatus 300, and the communication paths W21, W13, and W32 described in FIG. It forms part of the ring network that forms. Further, the routes transmitted in the order of the SDH device 300, the communication channel W31, the duplexed SDH device 100, the communication channel W12, and the duplexed SDH device 200 are the duplexed SDH devices 100 and 200, the SDH device 300 described in FIG. It forms part of a ring network formed by communication paths W12, W23 and W31.
That is, the SDH network 1 realizes a protection function by duplicating a communication signal between the external device 600 and the external device 700 and transmitting the duplicated signal through these two rings.

FIG. 10 is a diagram illustrating a path of a signal transmitted from the external apparatus 600 to the external apparatus 700 when the duplexed SDH apparatus 200 is in an execution state.
When a signal addressed to the external device 700 is transmitted from the external device 600, the external device communication unit 213 receives the signal and outputs it to the branching device 223. The branching device 223 duplicates the signal from the external device communication unit 213 and outputs it to the selector 231 and the selector 232.
Here, since the duplexed SDH apparatus 200 is in the execution state, the selector 231 outputs the signal from the branching unit 223 to the opposing device communication unit 211. The opposing device communication unit 211 transmits a signal from the selector 231 to the SDH device 300.
The signal transmitted from the opposing device communication unit 211 is received by the opposing device communication unit 312 and output to the selector 331.

In addition, since duplexed SDH apparatus 200 is in an execution state, selector 232 outputs a signal from branching unit 223 to overhead inserting unit 262. The overhead insertion unit 262 outputs the signal from the selector 232 to the redundant pair communication unit 212, and the redundant pair communication unit 212 transmits the signal to the duplexed SDH device 100.
The signal transmitted from the redundant pair communication unit 212 is received by the redundant pair communication unit 112 and transmitted in the order of the overhead monitoring unit 161, the branching device 122, and the selector 131. Here, since the duplexed SDH apparatus 100 is in a standby state, the selector 131 outputs a signal from the branching device 122 to the opposing device communication unit 111. The opposing device communication unit 111 transmits the signal from the selector 131 to the SDH device 300.
The signal transmitted from the opposing device communication unit 111 is received by the opposing device communication unit 311 and output to the selector 331.
The selector 331 performs an error check on the signal from the opposite device communication unit 311 and the signal from the opposite device communication unit 312, and outputs a signal that does not detect any error to the external device communication unit 313. The external device communication unit 313 transmits the signal from the selector 331 to the external device 700.

As described above, the signal transmitted from the external apparatus 600 is transmitted in the order of the duplexed SDH apparatus 200, the communication path W23, and the SDH apparatus 300, the duplexed SDH apparatus 200, the communication path W21, the duplexed SDH apparatus 100, and the communication path. W13 and the SDH device 300 are transmitted in this order and are transmitted twice.
The paths transmitted in the order of the duplexed SDH apparatus 200, the communication path W23, and the SDH apparatus 300 are the duplexed SDH apparatuses 100 and 200, the SDH apparatus 300, and the communication paths W12, W23, and W31 described in FIG. It forms part of the ring network that forms. The paths transmitted in the order of the duplexed SDH apparatus 200, the communication path W21, the duplexed SDH apparatus 100, the communication path W13, and the SDH apparatus 300 are the duplexed SDH apparatuses 100 and 200, the SDH apparatus 300 described in FIG. It forms part of a ring network formed by communication paths W21, W13, and W32.
That is, the SDH network 1 realizes a protection function by duplicating a communication signal between the external device 600 and the external device 700 and transmitting the duplicated signal through these two rings.

As described above, the duplexed SDH apparatus 100 and 200 constitute the redundant pair 10 and the selectors 131, 132, 231 and 232 select the SDH signal according to the status of the duplexed SDH apparatus, thereby the duplexed SDH apparatus. Even when a failure occurs in itself or when a failure occurs in the communication path between the duplexed SDH device and the external device, the transmission service can be continued while maintaining the protection function.
Duplex SDH apparatuses 100 and 200 communicate failure information using a failure information communication unit, and also insert failure information in the overhead portion of the VC path signal. In this way, since the failure information is transmitted twice, even if failure information communication by any means becomes impossible, such as when a failure occurs in the failure information communication unit or overhead insertion unit, communication by other means is possible. The status of the duplexed SDH apparatus can be determined using the failure information to be used.

Further, since overhead insertion units 162 and 262 perform communication by inserting failure information into the overhead portion of the VC path signal, it is not necessary to newly provide communication means for communicating failure information, and the device configuration can be simplified. .
Further, the duplexed SDH devices 100 and 200 shut down the external device communication unit so as not to communicate with the external device 600 when the duplexed SDH device is in a standby state. Need only communicate with either one of the duplexed SDH devices 100 and 200. Therefore, there is no load for receiving signals from both the duplexed SDH apparatuses 100 and 200 and performing error checking to select one of the signals or transmitting to both the duplexed SDH apparatuses 100 and 200. Just do it.

A program for realizing all or part of the functions of duplexed SDH apparatuses 100 and 200 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. The processing of each unit may be performed as necessary. Here, the “computer system” includes an OS and hardware such as peripheral devices.
Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 SDH network 100, 200 Duplex SDH apparatus 300 SDH apparatus 111, 211, 311, 312 Opposite apparatus communication part 112, 212 Redundant pair communication part 113, 213, 313 External apparatus communication part 121, 122, 123, 221, 222, 223 , 321 Branch 131, 132, 133, 231, 232, 233, 331 Selector 161, 261 Overhead monitoring unit 162, 262 Overhead insertion unit 171, 271 Fault information generation unit 172, 272 Fault information communication unit 173, 273 State determination unit 173

Claims (7)

A redundant pair comprising a main transmission device and an alternative transmission device,
The main transmission device determines a state of the first transmission device, a first redundant pair communication unit, a first external device communication unit, and the main transmission device to be either an execution state or a standby state. An apparatus state determination unit,
In the alternative transmission device, when the second opposing device communication unit, the second redundant pair communication unit, the second external device communication unit, and the main transmission device state determination unit determine the state of the main transmission device as the execution state Alternative transmission device state determination that determines the state of the alternative transmission device as a standby state, and determines the state of the alternative transmission device as an execution state when the main transmission device state determination unit determines the state of the main transmission device as a standby state And comprising
The first counter device communication unit and the second counter device communication unit send the same signal obtained by duplicating a signal addressed to an external device to the first counter device communication unit and the second counter device communication unit. It is possible to communicate with the transmitting opposite device that transmits,
The first redundant pair communication unit receives the same signal received by the first counter device communication unit when the main transmission device state determination unit determines that the state of the main transmission device is a standby state. To the communication department,
The second redundant pair communication unit receives the same signal received by the second opposite device communication unit when the alternative transmission device state determination unit determines that the state of the alternative transmission device is a standby state. To the communication department,
The first external device communication unit, when the main transmission device state determination unit determines the state of the main transmission device as an execution state, the same signal received by the first counter device communication unit and the first redundancy Of the same signal received by the pair communication unit, the signal that is not detected error is transmitted to the external device,
When the alternative transmission device state determination unit determines the state of the alternative transmission device as an execution state, the second external device communication unit receives the same signal received by the second counter device communication unit and the second redundancy The redundant pair, wherein the signal that is not detected in error among the same signals received by the pair communication unit is transmitted to the external device. The first redundant pair communication unit receives a signal received by the first external device communication unit from the external device when the main transmission device state determination unit determines the state of the main transmission device as an execution state. Send to the pair communication unit,
The second redundant pair communication unit receives a signal received by the second external device communication unit from the external device when the alternative transmission device state determination unit determines the state of the alternative transmission device as an execution state. Send to the pair communication unit,
The first counter device communication unit receives a plurality of signals received by the first external device communication unit from the external device when the main transmission device state determination unit determines the state of the main transmission device as an execution state. When a signal in which no error is detected among the signals is transmitted to a reception-side counter device capable of transmitting to the destination of the signal, and the main transmission device state determination unit determines that the state of the main transmission device is a standby state, A redundant pair communication unit transmits a signal from the external device received from the second redundant pair communication unit to the reception-side counter device;
When the alternative transmission device state determination unit determines that the state of the alternative transmission device is an execution state, the second counter device communication unit receives a signal received by the second external device communication unit from the external device on the reception side When the alternative transmission device state determination unit determines that the state of the alternative transmission device is a standby state, the second redundant pair communication unit receives from the first redundant pair communication unit from the external device. The redundant pair according to claim 1, wherein a signal is transmitted to the reception-side counter device. The main transmission device is:
A main transmission device failure information generation unit for generating failure information of the main transmission device;
A first failure information communication unit for transmitting the failure information;
Comprising
The alternative transmission device is:
An alternative transmission device fault information generation unit for generating fault information of the alternative transmission device;
A second failure information communication unit for receiving failure information of the main transmission device transmitted by the first failure information communication unit;
The first redundant pair communication unit transmits failure information of the main transmission device,
The second redundant pair communication unit receives failure information of the main transmission device transmitted by the first redundant pair communication unit,
The alternative transmission device state determination unit includes failure information of the alternative transmission device, failure information of the main transmission device received by the second redundant pair communication unit or the second failure information communication unit, and the main information determined in advance. The redundant pair according to claim 1 or 2, wherein a state of the alternative transmission device is determined based on a priority of the transmission device and a priority of the alternative transmission device. The main transmission device includes an overhead insertion unit that inserts failure information of the main transmission device into an overhead portion of a signal transmitted by the first redundant pair communication unit,
4. The redundant pair according to claim 3, wherein the alternative transmission device includes an overhead monitoring unit that reads out failure information of the main transmission device from an overhead portion of a signal received by the second redundant pair communication unit. The said alternative transmission apparatus state determination part controls so that a said 2nd external apparatus communication part may not transmit a signal, if the state of the said alternative transmission apparatus is determined to be a standby state. The redundant pair according to item 1. A redundant pair signal transmission method comprising a main transmission device and an alternative transmission device,
A main transmission device state determination step in which the main transmission device determines the state of the main transmission device to be either an execution state or a standby state;
When the alternative transmission device determines the state of the main transmission device as an execution state in the main transmission device state determination step, the state of the alternative transmission device is determined as a standby state, and the main transmission device state determination step An alternative transmission device state determination step for determining a state of the main transmission device as a standby state and determining the state of the alternative transmission device as an execution state;
A first reception step in which the same signal obtained by duplicating the signal addressed to the external device is transmitted from the opposite device and received by the main transmission device and the alternative transmission device;
When the main transmission apparatus determines that the state of the main transmission apparatus is a standby state in the main transmission apparatus state determination step, the main transmission apparatus transmits the same signal received in the first reception step to the alternative transmission apparatus. One transmission step;
When the alternative transmission apparatus determines that the state of the alternative transmission apparatus is a standby state in the alternative transmission apparatus state determination step, the alternative transmission apparatus transmits the same signal received in the first reception step to the main transmission apparatus. Two transmission steps;
When the main transmission apparatus determines the state of the main transmission apparatus as an execution state in the main transmission apparatus state determination step, the same signal received in the first reception step and the second transmission step A third transmission step of transmitting, to the external device, a signal in which no error is detected among the same signals transmitted from the alternative transmission device;
When the alternative transmission device determines the state of the alternative transmission device as an execution state in the alternative transmission device state determination step, the same signal received in the first reception step and the first transmission step A fourth transmission step of transmitting, to the external device, a signal from which no error is detected among the same signals transmitted from the alternative transmission device;
A signal transmission method comprising: In a computer as a control unit of a transmission device including an opposing device communication unit, a redundant pair communication unit, and an external device communication unit,
A state determining step for determining the state of the transmission apparatus to be either an execution state or a standby state;
When the execution state is determined in the state determination step, the signal received by the external device communication unit is selected as a signal transmitted by the opposing device communication unit, and when the standby state is determined in the state determination step A first signal selection step of selecting a signal received by the redundant pair communication unit as a signal transmitted by the opposite device communication unit;
When the execution state is determined in the state determination step , the signal received by the external device communication unit is selected as the signal transmitted by the redundant pair communication unit, and when the standby state is determined in the state determination step And a second signal selection step of selecting a signal received by the opposing device communication unit as a signal transmitted by the redundant pair communication unit.

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