Control device and identification method

Abstract

A control device 9 identifies wavelength selective switches 12, 13 in which an abnormality has occurred, wherein two of the wavelength selective switches are disposed in each optical node 1 included in an optical transmission system, and the control device 9 comprises: a setting unit 91 that sets optical paths for measurement in a plurality of sections of the optical transmission system; and an identifying unit 92 that acquires, from an analyzing device 15 connected to each optical node, an analysis result indicating whether or not there is an abnormality in an optical signal on an optical path set in each section, and identifies any wavelength selective switch in which an abnormality has occurred on the basis of the analysis result.

Description

Control Device and Identification Method

[0001] The present disclosure relates to a control device and an identification method.

[0002] In an optical transmission system capable of large-capacity communication, communication interruption caused by a failure or the like has a huge impact on services, so high reliability and availability are required. Although general optical transmission systems have redundancy, the redundancy lost due to a failure or the like needs to be restored at an early stage, which causes sudden work for maintenance personnel.

[0003] International Publication No. 2023 / 162187

[0004] In a wavelength selective switch (WSS: Wavelength Selective Switch), filter abnormalities such as filter shift and filter tightening occur due to aging degradation of optical elements and the like. Filter abnormalities in wavelength selective switches cause degradation of transmission quality, transmission errors, and the like.

[0005] In Patent Document 1, for each wavelength selective switch, an analysis device (OSA: Optical Spectrum Analyzer) is disposed to identify the wavelength selective switch in which a filter abnormality has occurred. However, in Patent Document 1, it is necessary to dispose an analysis device for each wavelength selective switch. When an optical node includes two wavelength selective switches, two analysis devices are required for each optical node, which increases costs.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a technology capable of reducing the number of analysis devices required for identifying a wavelength selective switch in which an abnormality has occurred.

[0007] In order to achieve the above object, one aspect of the present disclosure is a control device for identifying a wavelength selective switch in which an abnormality has occurred, wherein two wavelength selective switches are disposed at each optical node included in an optical transmission system, the control device comprising: a setting unit that sets an optical path for measurement in a plurality of sections of the optical transmission system; and an identifying unit that acquires an analysis result indicating the presence or absence of an abnormality in an optical signal of the optical path set for each section from an analysis device connected to each optical node, and identifies the wavelength selective switch in which an abnormality has occurred based on the analysis result.

[0008] One aspect of the present disclosure is a method for identifying a wavelength selector switch that has malfunctioned, wherein two wavelength selector switches are provided at each optical node of an optical transmission system, optical paths for measurement are set up in multiple sections of the optical transmission system, analysis results indicating whether or not there is a malfunction in the optical signal of the optical path set up in each section are obtained from an analysis device connected to each optical node, and the wavelength selector switch that has malfunctioned is identified based on the analysis results.

[0009] This disclosure provides a technology that can reduce the number of analytical devices required to identify wavelength-selective switches that have malfunctioned.

[0010] Figure 1 is a diagram showing an example configuration of the optical transmission system of this embodiment. Figure 2 is a diagram illustrating the optical path of this embodiment. Figure 3 is a diagram illustrating an example of the process for identifying a suspected WSS. Figure 4 is a diagram illustrating an example of the process for identifying a suspected WSS. Figure 5A is an example of the spectrum of an optical signal where filter shift is occurring. Figure 5B is an example of the spectrum of an optical signal where filter tightening is occurring. Figure 6 is a flowchart showing the process by which the control device identifies a suspected WSS in the cases of Figures 3 and 4. Figure 7 is a flowchart showing the process for which the control device identifies a suspected WSS. Figure 8 is a diagram illustrating an example of the process for identifying a suspected WSS by anomaly detection by the analysis unit. Figure 9 is an example of the hardware configuration.

[0011] Figure 1 shows an example of the configuration of the optical transmission system according to this embodiment.

[0012] The illustrated optical transmission system comprises an optical node 1, a multiplexing / demultiplexing unit 7, a transponder 8, and a control device 9.

[0013] The control device 9 is connected to the optical node 1, the multiplexing / demultiplexing unit 7, and the transponder 8 via a network, and monitors and controls these devices.

[0014] Optical node 1 is an optical transmission device that performs optical signal branching and insertion. For example, an ROADM (Reconfigurable Optical Add-Drop Multiplexer) device can be used as optical node 1.

[0015] The optical transmission system of this embodiment comprises a plurality of optical nodes 1, which are connected via optical fibers. The illustrated optical communication system shows four optical nodes 1, but is not limited to this.

[0016] The illustrated optical node 1 comprises a first amplifier 11, a first WSS (Wavelength Selective Switch) 12, a second WSS 13, a second amplifier 14, an analysis unit (analysis device) 15, and a signal transmission unit 16.

[0017] The first amplifier 11 and the second amplifier 14 are optical amplifiers (optical amplification devices) that amplify the input optical signal. The first amplifier 11 is located before the first WSS 12, amplifies the optical signal input via the optical fiber, and outputs it to the first WSS 12. The second amplifier 14 is located after the second WSS 13, amplifies the optical signal output from the second WSS 13, and outputs it to the optical fiber.

[0018] The first WSS 12 and the second WSS 13 are wavelength-selective switches that output the input optical signal to an arbitrary path (port). The optical node 1 of this embodiment includes two WSSs, the first WSS 12 and the second WSS 13. The first WSS 12 is a Pre WSS that drops the optical signal. The second WSS 13 is a Post WSS 13 that adds the optical signal. The first WSS 12 is provided after the first amplifier 11, and the second WSS 13 is provided after the first WSS 12.

[0019] The analysis unit 15 is a device that analyzes (monitors) the optical signal. The analysis unit 15 may perform spectral analysis of the optical signal using, for example, an OSA (Optical Spectrum Analyzer 1). In this embodiment, the analysis unit 15 is positioned between the first amplifier 11 and the first WSS 12 and analyzes the optical signal output from the first amplifier 11 (the optical signal between the first amplifier 11 and the first WSS 12). Specifically, the analysis unit 15 in this embodiment is positioned before the first WSS 12, which is a generally possible configuration, and transmits the analysis results indicating whether or not there is an abnormality in the optical signal to the control device 9.

[0020] The analysis unit 15 may be located inside the optical node 1 as shown in the figure, or it may be located outside the optical node 1. In other words, the analysis unit 15 only needs to be connected to the optical node 1.

[0021] The signal transmission unit 16 is a device that generates and transmits optical signals for measurement. The optical signals for measurement may be pseudo-optical signals (pseudo-light). Pseudo-optical signals do not need to be modulated (they do not need to contain information), but their spectral shape is the same as that of optical signals.

[0022] The signal transmission unit 16 is connected to the second WSS 13, generates a measurement optical signal, and outputs the measurement optical signal to the second WSS 13. The signal transmission unit 16 may be located inside the optical node 1 as shown in the figure, or it may be located outside the optical node 1. The signal transmission unit 16 does not have to be directly connected to the second WSS 13. For example, the signal transmission unit 16 may be located under the control of the multiplexing / demultiplexing function unit 7 which is connected to the second WSS 13, and connected to the second WSS 13 via the multiplexing / demultiplexing function unit 7.

[0023] The multiplexing / demultiplexing unit 7 is connected to the optical node 1 and combines or demultiplexes the passing optical signal. In the illustration, the multiplexing / demultiplexing unit 7 is located outside the optical node 1, but the multiplexing / demultiplexing unit 7 may also be located inside the optical node 1.

[0024] Transponder 8 transmits and receives optical signals with opposing transponder 8 via optical node 1. Transponder 8 is an optical transmission device that accommodates user equipment (not shown) and converts between electrical signals from the user equipment and optical signals output from the multiplexing / demultiplexing unit 7.

[0025] The control device 9 identifies the WSS 12 and 13 that have experienced abnormalities. The WSS 12 and 13 that have experienced abnormalities may also include suspected WSS 12 and 13 that are suspected of having abnormalities, and degraded WSS 12 and 13. The control device 9 may use an Operation System (OpS) that controls the optical transmission system, or it may use a device separate from the Operation System.

[0026] The illustrated control device 9 comprises a setting unit 91 and a specification unit 92. The setting unit 91 sets up optical paths for measurement in multiple sections of the optical transmission system. Specifically, if the analysis result of the optical signal in the first optical path set between the first optical node 1 and the third optical node 1, which is connected to the first optical node 1 via the second optical node 1, shows an abnormality, the setting unit 91 may set up a second optical path between the first optical node 1 and the second optical node 1, and a third optical path between the second optical node 1 and the third optical node 1.

[0027] The setting unit 91 may set up optical paths for measurement in two spans, from the transmitting optical node 1 that receives an abnormal signal from the transponder 8 or analysis unit 15 and transmits the optical signal output to the transponder 8 or analysis unit 15, to the receiving optical node 1 connected to the transponder 8 or analysis device 15.

[0028] The identification unit 92 obtains analysis results from the analysis unit 15 connected to each optical node 1 indicating whether or not there are abnormalities in the optical signals of the optical paths set in each section, and identifies the WSS 12 and 13 in which abnormalities occurred based on the analysis results. The identification unit 92 may also identify the WSS in which abnormalities occurred from among the WSS 12 and 13 provided by the first optical node 1 and the second optical node 1 based on the analysis results of the optical signals of the first optical path, the analysis results of the optical signals of the second optical path, and the analysis results of the optical signals of the third optical path.

[0029] Figure 2 is a diagram illustrating the optical path in this embodiment.

[0030] In this embodiment, the optical transmission system sets an optical path using an optical signal transmitted from the signal transmission unit 16. This optical path can be used for measuring the quality of the optical path. In this embodiment, not only single-span measurement optical paths 211 and 212, but also a multi-span measurement optical path 21 is set dynamically.

[0031] Single-span measurement optical paths 211 and 212 refer to optical paths established between adjacent optical nodes. Multiple-span measurement optical paths 21 refer to optical paths established across three or more consecutive optical nodes. The measurement optical path 21 shown in Figure 2 represents an optical path spanning two spans.

[0032] In this embodiment, the optical path for measurement is dynamically set to multiple sections, and by analyzing whether or not there is an abnormality in the optical signal of each section, WSS 12 and 13 indicating filter abnormalities are uniquely identified. In this embodiment, since only one analysis unit 15 is required for each optical node, the number of analysis units 15 required can be reduced.

[0033] In the illustrated example, three optical nodes 1A, 1B, and 1C are shown. Here, optical node 1A is a transmitting node, optical node 1B is a relay node, and optical node 1C is a receiving node. When an optical path is passed from the signal transmitting unit 16 (the transmitting end of the measurement signal) of optical node 1A to the analysis unit 15 of optical node 1C via optical node 1B, the optical path 21, which spans two spans, passes through three WSSs. That is, the optical path 21 passes through the second WSS 13 of optical node 1, and the first WSS 12 and second WSS 13 of optical node 1B.

[0034] Each single-span optical path 211, 212 passes through only one WSS. That is, optical path 211 is an optical path from optical node 1A to optical node 1B and passes through only the first WSS 12 of optical node 1A. Optical path 212 is an optical path from optical node 1B to optical node 1C and passes through only the second WSS 13 of optical node 1B. In this embodiment, the difference between the WSSs 12 and 13 that pass through each optical path 21, 211, and 212 is used to identify the suspected abnormal WSS (degraded WSS). Here, the first WSS 12 of optical node 1B is assumed to be the suspected WSS.

[0035] Figures 3 and 4 illustrate an example of the process performed by the control device 9 to identify suspected abnormal WSS 12 and 13.

[0036] In the illustrated example, an operational optical path S (service optical path) is established between the transponder 81 of optical node 1A and the transponder 82 of optical node 1D, and the transponder 8, which is the receiving end of optical path S, detects a degradation in the quality or an error in the received optical signal. The transponder 8 monitors the incoming optical signal and, upon detecting a degradation in the quality or an error in the optical signal, transmits an abnormality signal to the control device 9. The control device 9, triggered by the receipt of the abnormality signal, starts the following processing.

[0037] Specifically, when the control device 9 receives an abnormal signal from the transponder 82, it sets up measurement optical paths 31 and 32 every two spans in the optical path S (suspected section) where the abnormality was detected. That is, the setting unit 91 of the control device 9 receives the abnormal signal from the transponder 82 and sets up measurement optical paths 31 and 32 every two spans in the section from the transmitting optical node 1A that transmitted the optical signal output to the transponder 8 to the receiving optical node 1D connected to the transponder 8. The optical paths 31 and 32 have overlapping sections (parts). The control device 9 sets up the optical paths 31 and 32 by transmitting control signals to each optical node 1A, 1B, 1C, and 1D included in the optical path S.

[0038] With respect to the optical path 31, the control device 9 instructs the signal transmission unit 16 of the optical node 1A to transmit a measurement optical signal to the first WSS 12 of the optical node 1C. Then, the control device 9 instructs the analysis unit 15 of the optical node 1C to analyze the optical signal of the optical path 31.

[0039] With respect to the optical path 32, the control device 9 instructs the signal transmission unit 16 of the optical node 1B to transmit a measurement optical signal to the first WSS 12 of the optical node 1D. Then, the control device 9 instructs the analysis unit 15 of the optical node 1D to analyze the optical signal of the optical path 32.

[0040] The analysis unit 15 of the optical node 1C analyzes (measures) the optical spectral data of the optical signal for measurement in the optical path 31 and uses the optical spectral data to determine whether or not there is an abnormality in the optical signal in the optical path 31. In other words, the analysis unit 15 determines whether or not there is an abnormality in the filters of WSS 12 and 13 that pass through the optical path 31. Filter abnormalities such as filter shift and filter tightening occur in WSS 12 and 13 due to the aging of optical elements. Filter abnormalities in WSS 12 and 13 cause a decrease in the transmission quality of the optical signal and transmission errors. For example, if filter shift or filter tightening occurs, the analysis unit 15 determines that a filter abnormality (an abnormality in the optical signal) has occurred. The analysis unit 15 of the optical node 1C transmits the analysis result indicating whether or not there is an abnormality in the optical signal to the control device 9.

[0041] Similarly to the analysis unit 15 of the optical node 1C, the analysis unit 15 of the optical node 1D also analyzes optical spectrum data of the measurement optical signal in the optical path 32, determines whether there is an abnormality in the optical signal in the optical path 32 using the optical spectrum data, and transmits an analysis result indicating whether there is an abnormality in the optical signal to the control device 9. Note that general techniques can be used to determine whether there is a filter abnormality.

[0042] FIGS. 5A and 5B show an example of the spectrum of an optical signal when a filter abnormality occurs. FIG. 5A is an example of the spectrum of an optical signal when a filter shift occurs. FIG. 5B is an example of the spectrum of an optical signal when filter tightening occurs.

[0043] In the example shown in FIG. 3, the analysis unit 15 of the optical node 1C determines that a filter abnormality has occurred in the optical path 31, and the analysis unit 15 of the optical node 1D determines that no filter abnormality has occurred in the optical path 32.

[0044] As shown in FIG. 4, the control device 9 receives analysis results from the optical node 1C and the optical node 1D, and sets single-span optical paths 311 and 312 for the optical path 31 that has been determined to have a filter abnormality.

[0045] Specifically, for the optical path 311, the control device 9 transmits a control signal to each of the optical nodes 1A and 1B included in the optical path 311 to instruct setting of the optical path 311. The control device 9 instructs the signal transmitting unit 16 of the optical node 1A to transmit a measurement optical signal to the first WSS 12 of the optical node 1B. Then, the control device 9 instructs the analysis unit 15 of the optical node 1B to analyze the optical signal of the optical path 311.

[0046] For the optical path 312, the control device 9 transmits a control signal to each of the optical nodes 1B and 1C included in the optical path 312 to instruct setting of the optical path 312. The control device 9 instructs the signal transmitting unit 16 of the optical node 1B to transmit a measurement optical signal to the first WSS 12 of the optical node 1C. Then, the control device 9 instructs the analysis unit 15 of the optical node 1C to analyze the optical signal of the optical path 312.

[0047] The analysis unit 15 of the optical node 1B analyzes optical spectrum data of the measurement optical signal in the optical path 311, determines whether there is a filter abnormality in the optical path 311, and transmits the analysis result to the control device 9.

[0048] The analysis unit 15 of the optical node 1D analyzes optical spectrum data of the measurement optical signal in the optical path 312, determines whether there is a filter abnormality in the optical path 312, and transmits the analysis result to the control device 9.

[0049] The control device 9 uniquely identifies a suspected WSS suspected of having an abnormality (deterioration) based on the analysis results of the three optical paths 31, 311, and 312 determined by each analysis unit 15. Here, the WSSs through which the optical path 31 passes are the second WSS 13 of the optical node 1A, and the first WSS 12 and the second WSS 13 of the optical node 1B. The WSS through which the optical path 311 passes is the second WSS 13 of the optical node 1A. The WSS through which the optical path 312 passes is the second WSS 13 of the optical node 1B.

[0050] FIG. 6 is a flowchart showing a process in which the control device 9 identifies a suspected WSS in the cases of FIG. 3 and FIG. 4.

[0051] When the analysis result of the optical path 31 indicates a filter abnormality (when a filter abnormality is detected in the optical path 31) (S11: YES), and the analysis result of the optical path 311 indicates a filter abnormality (S12: YES), the control device 9 identifies that the second WSS 13 of the optical node 1A is the suspected WSS (S15).

[0052] When the analysis result of the optical path 311 is normal (when no filter abnormality is detected in the optical path 311) (S12: NO), and the analysis result of the optical path 312 is also normal (S13: NO), the control device 9 identifies that the first WSS 12 of the optical node 1B is the suspected WSS (S14).

[0053] When the analysis result of the optical path 312 indicates a filter abnormality (S13: YES), the control device 9 identifies that the second WSS 13 of the optical node 1B is the suspected WSS (S16).

[0054] If the analysis result of the optical path 31 is normal, that is, if no filter abnormality is detected in the optical path 31 (S11: NO), the control device 9 determines that there is no suspected WSS and terminates.

[0055] Figure 7 is a flowchart that generalizes the flowchart in Figure 6.

[0056] In Figure 7, the optical nodes 1A, 1B, 1C, and 1D shown in Figures 3 and 4 are denoted as optical nodes i, i+1, i+2, i+3, and so on, from left to right. A two-span optical path is denoted as PL(i→i+2), and a single-span optical path is denoted as PL(i→i+1). The two-span optical path PL(i→i+2) is the optical path that spans from optical node i through optical node i+1 to optical node i+2. The single-span PL(i→i+1) is the optical path from optical node i to optical node i+1.

[0057] The control device 9 identifies the second WSS 13 of optical node i as the suspected WSS if the analysis result of PL(i→i+2) is a filter abnormality (S21: YES) and the analysis result of PL(i→i+1) is a filter abnormality (S22: YES) (S25).

[0058] The control device 9 identifies the first WSS 12 of optical node i+1 as the suspected WSS if the analysis result of PL(i→i+1) is normal (S22: NO) and the analysis result of PL(i+1→i+2) is also normal (S23: NO).

[0059] If the analysis result of PL(i+1→i+2) is found to be a filter abnormality (S23: YES), the control device 9 identifies the second WSS 13 of optical node i+1 as the suspected WSS (S26).

[0060] If the analysis result of PL(i→i+2) is normal, that is, if no filter abnormality is detected in PL(i→i+2) (S21: NO), the control device 9 determines that there is no suspected WSS and terminates.

[0061] As shown in Figure 8, the control device 9 may identify the suspected WSS when the analysis unit 15 of the optical node 1C at the relay point detects a filter anomaly.

[0062] In Figure 8, an operational optical path S (service optical path) is established between the transponder 81 of optical node 1A and the transponder 82 of optical node 1D, and the analysis unit 15 of the relay point optical node 1C detects a filter anomaly in the received optical signal. Each analysis unit 15 monitors the incoming optical signal and, upon detecting a filter anomaly, transmits an anomaly signal to the control device 9. The control device 9, triggered by the receipt of the anomaly signal, starts the process of identifying the suspected WSS 12 and 13, which are suspected of having anomalies as described in Figures 3 to 7.

[0063] The control device 9 sets up optical paths spanning two spans, starting from the downstream side (receiving side) of the analysis unit 15 of the optical node 1C where the filter anomaly was detected. Here, the control device 9 sets up an optical path 21 spanning two spans from the transmitting node 1A to which the transponder 81 is connected to the optical node 1C where the filter anomaly was detected. Then, as in Figure 4, the control device 9 sets up single paths 211 and 212 and uniquely identifies the suspected WSSs 12 and 13 according to the flowchart shown in Figure 6 or Figure 7.

[0064] The control device 9 of this embodiment described above identifies the WSS 12, 13 in which an abnormality has occurred. The WSS 12, 13 are arranged in pairs at each optical node 1 of the optical transmission system. The control device 9 includes a setting unit 91 that sets measurement optical paths for multiple sections of the optical transmission system, and an identification unit 92 that obtains analysis results indicating whether or not there is an abnormality in the optical signal of the optical path set for each section from an analysis unit 15 connected to each optical node, and identifies the WSS 12, 13 in which an abnormality has occurred based on the analysis results.

[0065] The identification method of this embodiment is an identification method performed by the control device 9 to identify WSS 12, 13 in which an abnormality has occurred. Two WSS 12, 13 are provided at each optical node 1 of the optical transmission system. Optical paths for measurement are set in multiple sections of the optical transmission system. Analysis results indicating whether or not there is an abnormality in the optical signal of the optical path set in each section are obtained from an analysis device connected to each optical node, and the WSS 12, 13 in which an abnormality has occurred are identified based on the analysis results.

[0066] According to this embodiment, it is not necessary to provide an analysis unit 15 for each WSS 12 and 13; one analysis unit 15 is sufficient for each optical node 1. This reduces the number of analysis units 15 required for each optical node 1 in this embodiment.

[0067] Furthermore, in this embodiment, since abnormalities occurring in WSS 12 and 13, which are signs of failure, can be detected, suspected WSS 12 and 13 can be identified at the stage of predicting failure, allowing for preventive maintenance-type failure response and suppressing the sudden work of maintenance personnel.

[0068] The control device 9 of this embodiment described above can use, for example, a general-purpose computer system as shown in Figure 9. The illustrated computer system includes a CPU (Central Processing Unit, processor) 901, a memory 902, a storage device 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906. The memory 902 and the storage device 903 are storage devices. In this computer system, each function of the control device 9 is realized when the CPU 901 executes a predetermined program loaded onto the memory 902.

[0069] Furthermore, the control device 9 may be implemented on one computer or on multiple computers. The control device 9 may also be a virtual machine implemented on a computer. The program of the control device 9 can be stored on a computer-readable recording medium such as an HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or it can be distributed over a network. A computer-readable recording medium is, for example, a non-transitory recording medium.

[0070] This disclosure is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence.

[0071] 1, 1A, 1B, 1C, 1D: Optical nodes 11: First amplifier (optical amplifier) ​​12: First WSS (wavelength selector switch) 13: Second WSS (wavelength selector switch) 14: Second amplifier 15: Analysis unit (analysis device) 16: Signal transmission unit 7: Multiplexing / demultiplexing unit 8, 81, 82: Transponder 9: Control unit 91: Setting unit 92: Identification unit

Claims

1. A control device for identifying a wavelength selector switch in which an abnormality has occurred, wherein two wavelength selector switches are provided at each optical node of an optical transmission system, the control device comprising: a setting unit for setting optical paths for measurement to multiple sections of the optical transmission system, and an identification unit for obtaining analysis results indicating whether or not there is an abnormality in the optical signal of the optical path set to each section from an analysis device connected to each optical node, and identifying the wavelength selector switch in which the abnormality has occurred based on the analysis results.

2. The control device according to claim 1, wherein if the analysis result of the optical signal of the first optical path set between the first optical node and the third optical node connected to the first optical node via the second optical node indicates an abnormality, the setting unit sets a second optical path between the first optical node and the second optical node, and sets a third optical path between the second optical node and the third optical node, and the identification unit identifies the wavelength selector switch from among the wavelength selector switches provided in the first optical node and the second optical node that has experienced an abnormality, based on the analysis result of the optical signal of the first optical path, the analysis result of the optical signal of the second optical path, and the analysis result of the optical signal of the third optical path.

3. The control device according to claim 1, wherein the setting unit receives an abnormal signal from the transponder or the analysis device and sets up measurement optical paths in two spans from the transmitting optical node that transmits the optical signal output to the transponder or the analysis device to the receiving optical node connected to the transponder or the analysis device.

4. A method for identifying a wavelength selector switch in which an abnormality has occurred, performed by a control device, wherein two wavelength selector switches are provided at each optical node of an optical transmission system, optical paths for measurement are set up in multiple sections of the optical transmission system, analysis results indicating whether or not there is an abnormality in the optical signal of the optical path set up in each section are obtained from an analysis device connected to each optical node, and the wavelength selector switch in which the abnormality has occurred is identified based on the analysis results.

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