JP2008301509A - Signal switching apparatus and transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a more highly reliable reserve switching system. <P>SOLUTION: With respect to an active system under operating, first and second reserve routes are provided, the second reserve route is shared among a plurality of first reserve routes, and the first and the second reserve routes are connected with a signal selecting section via a signal switching section. The first reserve route is monitored. When a fault is detected, in timing of the fault detection, the reserve route to be connected with the signal selecting section is automatically switched from the first to the second reserve route by 1:N switching or restoration, so that the reserve system that is a switching destination is maintained normal even under active system failure and reliability improvement is attained. Furthermore, the second reserve route is shared among a plurality of first reserve routes, so that the system becomes economical. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to standby switching, and more particularly to a reliable and high-speed standby switching of a communication network and an optical transmission system using the same.

  With the rapid increase in data traffic represented by the Internet in recent years, the transmission capacity of communication networks has been increasing. At present, when transmission opticalization is put into practical use, the capacity is increased by using time division multiplexing technology and optical wavelength multiplexing technology.

  There is a 10 Gbps transmission device per channel, or a wavelength multiplex transmission device that can multiplex several channels to several tens of channels with a single fiber and can transmit over a long distance using an optical amplifier or a regenerative repeater. It has been put into practical use.

  On the other hand, mesh-type optical networks are being studied in order to cope with future increases in demand, further economics, and diversification of services. By making the optical network mesh-type, the degree of freedom of route setting is improved, so it is expected that the degree of freedom for faults is high, automatic and high-speed recovery is possible, and the reliability of the network can be improved. Yes. In addition, since the spare capacity can be selected so that the necessary line is used when necessary, it is considered that the spare system can be shared by a plurality of working paths and the entire network can be realized economically.

  In order to realize the mesh type optical network as described above, an optical signal switching device or an optical cross-connect that can accommodate an optical signal such as STM-64 / OC-192 as an input / output interface and performs path switching or switching to a standby device. The development of a device called "" is underway. The optical cross-connect can switch the connection relationship between transmission lines connected to a certain node or the connection relationship between a transmission line and a user device by automatic or remote control. In addition, optical cross-connects that switch using optical switches without converting optical signals into electrical signals are capable of processing large-capacity information that is difficult to achieve with electronic circuits, while increasing the capacity of node processing information. It is expected to be able to do.

  In general, as a communication network switching method, several redundant configurations such as 1 + 1 switching and 1: N switching are used. For example, in the 1 + 1 switching, when the signal is split into two on the transmission side, and one is used to transmit / receive a signal in operation as the active system, the other is used as a standby system, and when the failure on the active system is detected on the reception side, Switch the operating signal to the standby system. In the 1: N switching, one standby system is shared with a plurality of active systems, and a control signal is exchanged between a transmitting node and a receiving node for a system in which a failure occurs among a plurality of active systems, and transmission / reception is performed. Switch to the standby system using both switching devices. As conventional techniques related to 1 + 1 switching and 1: N switching, for example, a preliminary switching method described in “Patent No. 2722879 (Patent Document 1)” and “No. 2746203 (Patent Document 2)” are described. There is a transmission line uninterruptible switching system. As a related art relating to 1 + 1 switching that performs switching using an optical signal or an electric signal, there is an optical 1 + 1 switching device described in “Japanese Patent Laid-Open No. 2002-51209 (Patent Document 3)”.

  Among these switching methods, the 1 + 1 switching is performed by judging the normality of the signal only on the receiving side, so other methods that require switching after performing communication control on both the transmitting side and the receiving side Compared to, it has the feature of being able to recover from failures at high speed.

  Here, as an example of recovery time due to 1 + 1 switching, when switching is performed using an electrical signal, recovery can be performed without instantaneous interruption by using a delay circuit, a time difference detection circuit, etc., that is, without causing the user to sense a failure. In the case of recovery using an optical signal, the recovery can be performed in several milliseconds to several tens of milliseconds. Further, according to the above-mentioned “Japanese Patent Laid-Open No. 2002-51009 (Patent Document 3)”, a high-reliability and high-speed 1 + 1 switching device can be realized by performing performance monitoring not only on optical power but also on an electrical level. This can be realized and contributes to high reliability of the optical network.

  By combining such a 1 + 1 switching device and the above-described mesh type optical network, it is considered that an economical network that can recover from a failure at high speed can be realized.

  As a technique related to the optical switch used in the above-described signal switching device or 1 + 1 switching device, for example, an optical waveguide movable optical switch as shown in “JP-A-9-159936 (Patent Document 4)”, Optical waveguide non-movable optical switch as disclosed in “Japanese Patent Laid-Open No. 10-10588 (Patent Document 5)”, and micromachine type optical switch as illustrated in “Japanese Patent Laid-Open No. 2002-169107 (Patent Document 6)” Etc. are known.

Japanese Patent No. 2722879 Japanese Patent No. 2746203 JP 2002-51009 A JP-A-9-159936 Japanese Patent Laid-Open No. 10-10588 JP 2002-169107 A

  When applying 1 + 1 switching within a mesh network using an optical cross-connect or the like, the following problems are expected. Since the degree of freedom of route selection increases, the transmission distance between the transmission node and the reception node increases for both the working route and the backup route, and the number of devices arranged on the working route and the backup route also increases. Along with this, the frequency of failure occurrence in each route also increases. In addition, as the speed of user interface signals increases, the types of data contained in one signal and the required level of reliability are expected to diversify, and depending on the services provided, it will be more than ever. Therefore, a highly reliable switching method may be required. However, in the conventional 1 + 1 switching device, the standby transmission line as a switching destination is fixedly determined with respect to the active system, and even if only the failure of the standby system occurs, the standby system is automatically restored. Therefore, if a failure occurs in the active system when a double failure occurs, for example, the backup path is out of service due to failure or maintenance, the line may not be temporarily restored. The time interval that cannot be restored here is the repair time by the working or standby system. If the respective repair times are Trw and Trp, the line recovery time is the smaller of Trw and Trp. Usually, Trw and Trp were almost equal, and several hours were required.

  In order to solve the above-described problem, the standby switching method of the present invention includes a second standby path in addition to the first standby path that is a normal switching destination when the active system that accommodates a signal in operation has failed. When the first backup path and the second backup path are accommodated in the signal switching device, the first backup path status is monitored, and a failure occurs in the first backup path, etc. In this case, the switchover destination at the time of failure of the active system is automatically switched to the second backup path using the signal switching device triggered by the detection of the state change, so that the backup destination that is the switchover destination of the active system The system was maintained normally.

  More specifically, the preliminary switching method according to the present invention uses a signal switching device including a branching unit, a signal switching unit, a signal monitoring unit, and a signal selection unit, and an active path on the transmission path side of the signal switching unit. Connect the first backup path and the second backup path, connect the branching unit and the signal selection unit to the user device side of the signal switching device, and detect the state change of the signal from the first backup path in the signal monitoring unit. As a trigger, the signal switching unit is controlled to automatically switch the input of the signal selection unit from the first backup path to the second backup system, thereby reducing the standby time of the standby system.

According to the optical signal switching method of the present invention, the standby system can always be maintained normally by automatically switching the standby system to another normal standby system upon detection of a failure in the standby system. It is possible to realize a redundant configuration that can cope with a double failure in a transmission line or device. Further, according to the standby switching method according to the present invention, a highly reliable 1 + 1 redundant configuration can be provided as described above, and thus a quick and highly reliable optical transmission system can be provided.

  In the embodiment of the present invention, the preliminary switching is performed by using a signal switching device including a branching unit, a signal switching unit, a signal monitoring unit, and a signal selection unit. Connect the backup path and the second backup path, connect the branching unit and the signal selection unit to the user device side of the signal switching device, and detect the change in the state of the signal from the first backup route in the signal monitoring unit By controlling the signal switching unit, the input of the signal selection unit is automatically switched from the first backup path to the second backup system to reduce the standby time of the standby system.

Further, the standby switching according to the present embodiment enables each of the first backup paths in the plurality of 1 + 1 switching devices and the number of second backup paths fewer than the 1 + 1 switching devices to be connected to each other by the signal switching unit. When a failure in any of the first backup paths is detected, the signal switching unit is controlled to select the second backup path from which the change in state is detected among the plurality of first backup paths. Switch to the alternate route. As a switching method between the first backup route and the second backup route, 1: 1 switching by cooperative operation between two nodes, 1: N switching, restoration by cooperative operation of a plurality of nodes, and the like are used. .

Hereinafter , embodiments of optical standby switching and an optical network using the same will be described in detail with reference to the drawings.

It shows an embodiment of an optical signal switching device in applying a preliminary switching scheme in FIG. The signal switching device 101 includes a signal switching unit 131, a branching unit 111 that branches a user signal for redundancy, and a device monitoring control unit 141 that monitors and controls the entire device. The signal switching apparatus 101 transmits a user signal or a signal including a user signal to the signal switching apparatus 102 via the working path 201, the first backup path 211, and the second backup path 221. The signal switching device 102 receives the received signals from the paths 201, 211, and 221, monitors the signal status of the working path and the backup path with the signal monitoring units 271 and 272, selects a normal signal with the selection unit 122, Outputting to the user device. Normally, when the working path is normal, connections indicated by thick dotted lines in the signal switching units 131 and 132 are set. When a failure occurs in the working path, the selection unit 122 of the switching device 102 on the reception side selects a signal from the first backup path via the connection within the switching unit indicated by the thick dashed-dotted line and outputs it to the user device.

  That is, when both the working path and the first backup path are normal, the signal from the user device is branched by the branching unit 111, and one signal is given to the selection unit 122 in the signal switching device 102 through the working path 201. It has been. The other signal is also given to the selector 122 through the first backup path 211. The selection unit 122 selects a signal from the working path when the working path is normal, and selects a signal from the first backup path when the working path is abnormal.

An example of a signal switching procedure will be described with reference to FIGS. The first backup path is monitored by the backup path signal monitoring unit 272 (S001). When a failure such as a signal break in the signal from the first backup path or an error rate threshold value exceeded is detected, the device monitoring control unit 142 senses this, and the device monitoring control units 141 and 142 communicate with each other. The signal switching units 131 and 132 are controlled, and switching is performed from the thick one-dot chain line to the connection indicated by the thin one-dot chain line as indicated by the arrows in the drawing (S003). In order to prevent a malfunction of the system due to the operation of the active signal selection unit during the standby switching operation, the operation of the signal selection unit is temporarily suspended during the standby switching operation (S002). After completion, the temporary hold is released (S004). If there is no change or deletion of the set route, monitoring is continued. If there is a route deletion or change command from the external monitoring control device, this switching procedure for the route is terminated (S005).

Here, in order to make the explanation easy to understand, the present embodiment refers to the case of one-way communication and the case where there is one signal from the user device. However, it is obvious that there is an effect of the present embodiment . In the case of bidirectional communication, the branching unit and the selection unit are installed in both the signal switching devices 101 and 102. When there are a plurality of signals from the user apparatus, the same number of branching units and selection units as the user signals are set. In this case, the second backup path can be shared by the first backup paths of the plurality of user signals. When switching between the first and second standby systems, as described above, the device monitoring control units may communicate directly with each other, or the external monitoring control unit receiving information from the monitoring control unit The signal switching units 131 and 132 may be controlled via the device monitoring control unit.

The configuration of the optical signal switching device which is another embodiment of the spare switching method will be described with reference to FIG. Optical signal switching device 103 includes device monitoring control unit 143, the optical switch 133, Netw network interface 163 with an optical input and output, the user interface 153 with an optical input, an optical branch selection section 173. The optical branch selection unit 173 includes an optical splitter 113 for branching a user signal into an active path and a backup path, and an optical selector 123 for selecting a signal from the current path and the backup path and outputting the signal to the user apparatus. . The network interface 163 includes a current route 163-1, a first backup route 163-2, and a second backup route 163-3. The user interface 153 includes an active system 153-1 and a standby system 153-2.

  A configuration example of the user interface 153 is shown in FIG. The user interface 154 includes optical receivers 261 and 262, optical transmitters 251 and 252, and a signal monitoring / signal processing unit 273. The optical transmitter 252 is connected to the optical selector 123 of FIG. 3, and the optical receiver 262 is connected to the optical splitter 113. The optical transmitter 251 and the optical receiver 261 are connected to the optical signal switching device 103. The signal monitoring / signal processing unit 273 performs, for example, signal monitoring / processing including frame synchronization, parity check, signal processing, speed conversion, error correction code processing, and the like. Depending on the situation, either may not be performed. Here, the configuration example of the user interface is shown, but the network interface 163 can also be realized with a substantially similar configuration.

  A configuration example of the device monitoring control unit 143 is shown in FIG. The device monitoring control unit 144 includes a CPU 310, a configuration information storage memory 320, an active / standby monitoring information storage memory 330, a switching control information storage memory 340, an external communication interface 350, a maintenance communication interface 360, and a device interface 370. Yes.

Figure 6 shows the example of the procedure for performing the optical signal switching according to this embodiment using the apparatus shown in FIGS. 3 to 5 as an operation flows. When this apparatus starts operation, the active user interface 153-1 selected by the optical selector, that is, the active user interface 153-1 that is in operation, and the standby user interface that is not selected by the optical selector, that is, is not operating 153-2 is monitored (S111, S121). As a result of monitoring the active user interface 153-1, when a failure is detected, the state of the standby user interface 153-2 is first checked in order to switch to the standby system (S112). Here, the monitoring result of the standby user interface, the switching status of the standby system, and the like are confirmed. As a result, if the standby system is normal and can be switched, the optical selector 123 in FIG. 3 is switched to select the standby system. In this operation, the signal is restored. Thereafter, if there is no change in the set route, the monitoring is continued.

  On the other hand, if a failure is detected as a result of monitoring by the backup user interface 153-2, a backup path is determined based on a preset switching method (S122), and the optical switch unit 133 is controlled by the monitoring control unit 143 to perform backup. System recovery operation is performed (S123). At this time shown in FIG. 2, the optical switch section 133 is changed from the connection state indicated by the thick dashed line in FIG. 3 to the connection state indicated by the thin dashed line.

  Thereafter, after confirming that the signal is normal in the standby system user interface 153-2 (S124), if there is no change / deletion of the route, the monitoring is continued (S130). On the other hand, if the standby user interface 153-2 does not return to normal even after the switching of S123, the external monitoring control device is notified and a response is urged (S125).

  In this figure, in order to make the explanation easy to understand, the description of the temporary hold processing to the signal selection unit described in S002 and S004 in FIG. 2 is omitted. Similarly, although the description is omitted, it is also possible to notify the spare user IF of the failure to the external monitoring device or device monitoring control unit of S125 in parallel with the processing of S122 when the failure is detected in S121.

  Similarly, although not shown in this figure, after switching from the active system to the first standby system, the active transmission line 203 is used as the first standby path that is not in operation, and the first standby transmission line 213 is in operation It may be reset as a route. At this time, if a failure occurs in the working transmission line 203 that has become the first backup path, the second backup path is used for recovery, and the signal from the first backup transmission path 213 that has become the working system fails. May be switched to the second backup route.

  According to the present embodiment, the standby system is monitored, and when a failure occurs in the standby system, switching to another backup system is performed, and switching of the signal selection unit is performed by judging only at the reception side by using 1 + 1 switching. Therefore, it is not necessary to exchange control signals for the switching operation between the transmitting and receiving nodes, and high-speed and reliable failure recovery is possible.

In this embodiment, an example of an optical signal switching device using an optical selector and an optical splitter has been described. However, it is obvious that the effect of this embodiment is the same even when a 1 + 1 device using an electric circuit is used. The optical selector can use, for example, a commercially available 1 × 2 optical switch such as a waveguide type, an optical fiber drive type, or a micromachine type, and the optical splitter has one input and two outputs such as a fiber fusion type or a filter type. An input 2-output optical coupler or the like can be used.

Another embodiment according to preliminary switching scheme illustrated in FIG. In FIG. 7, the signal switching apparatus using the preliminary switching method according to this embodiment includes a signal switching unit 134, a user interface 154, and a network interface 164. The user interface 154 is connected to the user device 304 and the signal switching unit 134, the network interface 164 is connected to the transmission line and the signal switching unit 134. Here, the device monitoring control unit as indicated by 143 in FIG. 3 is omitted for easy understanding. User devices 304-1 to 304-1 and user interfaces 154-1 to 154-2 are configured by a network interface 164-1 to 164-2 and a signal switching device 134 in a 1: 3 redundant configuration (one spare for three active systems). In the normal state, no signal flows in the standby system, and if one of the active systems fails, the signal flows into the standby system). In this way, it is connected to the network interfaces 164-1 to 164-3. The network interface 164-4 is a standby system shared by the user interfaces 154-1 to 154-3. That is, the signal switching device 104 is connected to the user interface 154-2 by the signal switching unit 134 when, for example, a failure is detected in the received signal of the user interface 154-2 among the user interfaces 154-1 to 154-1. By switching the network interface to be changed from 164-2 to 164-4, the signal of the user interface 154-2 is restored.

  The user device 304-4 is protected with a 1 + 1 redundant configuration by the user interfaces 154-4 and 154-5, the signal branch selection unit 174, and the network interfaces 164-7 and 164-8. In other words, the transmission / reception signal of the user device 304-4 is split by the signal branch selection unit 174 so that the signal from the user device is split into two and the signal to the user device is switched to one of the two user interfaces. The user interfaces 154-4 and 154-5 are connected to the network interfaces 164-7 and 164-8 via the signal switching unit 134, as shown by the dotted lines in the figure. It is connected. At this time, (154-4, 164-7) is used as the active system and (154-5, 164-8) is used as the standby system as a combination of the user interface and the network interface. The switch part of the branch selection unit 174 indicates this. When the user interface 154-4 detects a failure in the received signal, the branch selection unit 174 operates to select the normal user interface 154-5 and connect to the user device 304-4. Thereby, the 1 + 1 preliminary switching operation is performed.

  Furthermore, since the signal switching unit 134 can connect the user interface 154-4 or 154-5 to the network interface 164-4, this constitutes a second standby system.

Network interface 164-5 and 164-6 are the connection shown by a dotted line in the signal switching unit 134 parts, by connecting the transmission line to each other, to function the apparatus as a relay node.

According to the standby switching method according to the present embodiment, the network interface 164-4 used for the 1: 3 redundancy configuration of the user devices 304-1 to 304-3 and the transmission path connected thereto are connected to the user device 304-4. Can be shared as the second standby system when the standby system of the 1 + 1 redundant configuration fails. That is, when a failure is detected in the standby system (154-5, 164-8) of the 1 + 1 redundant configuration, the network interface connected to 154-5 is changed to 164-8 by controlling the signal switching unit 134. Can be switched from 164 to 164-4, so that spare parts and spare transmission lines can be used efficiently and high reliability of 1 + 1 switching can be achieved.

  FIG. 8 is a diagram showing an example of an optical network in one embodiment of the present invention. The transmission / reception nodes 231 and 232 are signal switching devices as indicated by 101 to 104 in FIG. 1, FIG. 3, or FIG. These are connected by an active route 204, a backup route 214, and a second backup route 224. When the signal switching device is remote and there are nodes between them, the node between them functions as a relay node. As shown in the figure, for example, the working route 204 passes through the relay node 241, the backup route 214 passes through the relay route 242, and the second backup route 224 passes through the relay nodes 243 and 244. Here, when a failure occurs in the backup route 214, switching to the second backup route 224 is performed. Then, the same signal is transferred to the working path 204 and the second backup path 224. In this way, since a healthy backup path can be prepared prior to the failure of the working path 204, quick recovery can be achieved.

Preliminary switching method is not limited to the embodiments described above.
As a switching device for the signal switching units 131 to 134, the signal selection unit 122, or the signal branch selection units 173 and 174, a semiconductor integrated circuit may be used, or an optical switch that switches an optical signal as it is without converting it into an electrical signal. good. The optical switch may be a micromachine type, a movable optical waveguide type, a non-movable optical waveguide type, etc., as shown in the description of the prior art, and the degree of freedom of connectivity between the interfaces necessary for this embodiment , It may be adopted in consideration of the switching speed. As the switching speed, the effect of the present embodiment is effective if it is sufficiently faster than the time required for the maintenance personnel to replace parts when the standby system fails due to normal 1 + 1 switching. For example, this is used when the automatic standby path switching execution time according to the present embodiment is within a few tens of milliseconds, including the failure detection time, various control times, and the propagation time of control signals between nodes. As an optical switch, it is only necessary to be able to switch within a few milliseconds to a few dozen milliseconds or less.

As a second standby system selection method that is one of the procedures of the standby switching method of this embodiment as shown in S122 of FIG. 6, for example, 1: N standby switching is performed between a plurality of 1 + 1 redundant configurations. it also has good, a plurality of 1: between the spare system N redundancy, the spare system state, depending on the priority of each redundant system can be switched to each other. Further, switching may be performed by a recovery method for determining a backup route to be used between a plurality of nodes, so-called restoration. The restoration route may be calculated automatically or may be set by the operator based on human judgment. In the case of automatic setting, a route may be searched after detecting a failure, or a route is searched in advance before detecting a failure, and when a failure is detected, the route is switched to the predetermined second backup route shown on the left. May be. As a route search / setting method, a search may be arbitrarily performed between the transmission node and the reception node, or a backup route may be searched or set only in the vicinity where a failure has occurred.

  After switching to the standby system, after the active system has recovered normally due to parts replacement, etc., it may be switched back or not switched back, and the switched backup path becomes the new active system and recovered. The active system may be used as a new backup route.

In the above-described embodiment, an example of switching to the second standby system when a failure in the standby system is detected is shown. However, according to this embodiment, in the case of a 1: N switching device, 1 in the N active systems is already present. When one of them uses the first standby system, the switching control information of the 1: N switching system is updated to share the switching destination when another one in the working system fails. It can be made to be a second standby system.

Diagram illustrating a configuration example of a signal switching device. Operation flowchart showing an example of a signal switching procedure. The figure which shows the structural example of an optical signal switching apparatus. Diagram illustrating a configuration example of a User chromatography THE interface. Diagram showing a configuration example of instrumentation置監vision controller. Operational flow diagram showing another example of the signal switching procedure. Diagram showing another configuration example of a signal switching device. The figure which shows the structural example of an optical network.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101-104 ... Signal switching device, 111-113 ... Branch part or optical splitter, 122, 123 ... Selection part or optical selector, 131-134 ... Switching part or optical signal switching part or optical switch, 141-144 ... Device supervisory control 153, 154 ... user interface, 163, 164 ... network interface, 173, 174 ... branch selection unit, 201, 203, 204 ... working route, 211, 213, 214 ... first backup route, 221, 223, 224-... second backup path, 231, 232 ... transmission / reception node, 241-244 ... relay node, 251, 252 ... transmitter, 261, 262 ... receiver, 271-273 ... signal monitoring / signal processing unit, 304 ... user apparatus.

Claims (7)

A signal switching device for switching signals spare system and the active system,
Accommodates multiple, different or similar redundant lines,
A first signal switching unit for switching the redundant configuration of each of the plurality of redundant systems;
A second signal switching unit for switching between two or more standby systems used in at least two redundant configurations among the plurality of redundant configurations, a standby system monitoring unit,
And a means for switching the standby system used by the line according to the priority of the line protected by the backup system when a failure occurs in any of the two or more backup systems. Switching device. Includes a first signal switching unit having a selector signal branching unit, and said second signal switching unit that first signal switching unit and the working path and the first spare path and connected to the second spare path,
The second signal switching unit connects one output of the branching unit of the first signal switching unit and one input of the selection unit to the working path when normal, and the first signal switching unit when normal A signal switching unit that connects the other output of the branching unit and the other input of the selection unit to the first backup path, and the selection unit of the first signal switching unit when there is an abnormality in the working path Selects the signal from the first backup path and switches the second signal switching section so that the signal is communicated between the first signal switching section and the second backup path when there is an abnormality in the first backup path. A transmission system comprising a signal switching control unit. After switching to the spare path has occurred in the working path, the transmission system according to claim 2, characterized in that as a new preparatory route the repair has been the working path.   One end is connected to each of the optical branching unit and the optical selecting unit provided for one user device, one of them is the active user, the other is the first spare two user interfaces, and one end is the active transmission line Connected working network interface, first backup path network interface connected at one end to the first backup transmission path, second backup path network interface connected at one end to the second backup transmission path, and user interface The other end of the network interface and the other end of the network interface are connected to each other, and the first backup path is connected. If there is an abnormality in the first backup path, the connection destination of the first backup user interface is set to the second backup path network. A signal switching device comprising a switch for switching connection to an interface.   Means for transmitting / receiving the same signal by branching a signal to the working path and the backup path, wherein transmission / reception nodes are connected by a working path, a backup path and a second backup path through different relay nodes; When there is an abnormality in the transmission system, the transmission system further includes means for switching to transmit the same signal as that of the divided working to the second call path. After the failure of the first standby system and switching to the second standby system, if the first standby system is restored, the first standby system is replaced with the second standby system or another 2. The signal switching device according to claim 1 , wherein the signal switching device is a switching destination when a failure occurs in a standby system or another active system. 2. The signal switching device according to claim 1 , wherein the switching operation of the system by the first signal switching unit is controlled based on the information indicating the switching status of the standby system by the second signal switching unit.

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