Method and / or system for reducing number of redundant cable paths in an optical network

Abstract

Methods for reducing the number of redundant cable paths in a multi-path redundant fiber optic cable network are disclosed. A method includes: monitoring cable paths in the fiber optic cable network using distributed fiber optic sensing to detect cable break events; measuring cable break rates for the cable paths in the fiber optic cable network over a period of time based on the detected cable break events; determining availability of the fiber optic cable network over the period of time, the availability determined based on the number of redundant cable paths in the fiber optic cable network and the cable break rates of the cable paths; and providing an indication when the fiber optic cable network achieves a target availability with at least one less redundant cable path.

Description

METHOD AND / OR SYSTEM FOR REDUCING NUMBER OF REDUNDANT CABLEPATHS IN AN OPTICAL NETWORKTECHNICAL FIELD

[0001] The present disclosure generally relates to systems and methods for distributed sensing using one or more optical fibers. More particularly, aspects of the present disclosure relate to systems and methods for reducing redundancy in optical fiber networks using distributed fiber optic sensing (DFOS).BACKGROUND

[0002] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.

[0003] The majority of optical cables and utility infrastructure across cities are buried in public spaces along shared access ways like roads and streets. This infrastructure is typically also buried alongside a range of other assets, such as sewers, gas mains, water mains, electricity cables, etc. Fig. 1 illustrates a schematic of an example underground cross-section 100 under and adjacent to a road 102 and sidewalk 103. As seen in the schematic, fiber optic cables 104 may be buried under the road 102, along with gas mains 106, water mains 108, and electricity cables 110.

[0004] From time to time, the road 102 and / or the sidewalk 103 may be excavated to maintain, repair, or install new infrastructure underneath it. If these excavations are not conducted properly, they may damage or destroy one or more of the assets, such as the fiber optic cables 104. It will be appreciated that if a fiber optic cable is damaged or destroyed, it can drastically affect the ability of the cable to communicate data, and this can lead to catastrophic interruption to data services.

[0005] To address this, most fiber optic networks build in network redundancy - i.e., they provide multiple, geographically diverse cable paths to service the same client site. This way, if a primary cable path servicing a client is damaged or destroyed, one of the secondary oralternative cable paths can be used to service the client without interruption. Generally, the more geographically diverse cable paths in a network, the more robust the network is to any isolated cable incidents. However, increasing redundancy in a network increases the infrastructure costs and service costs to clients that use the optical network.

[0006] Accordingly, there exists a need for systems and methods that can aid in reducing network redundancy while maintaining the same level of data availability and uninteruptability.SUMMARY

[0007] According to a first aspect of the present disclosure there is provided a method for reducing the number of redundant cable paths in a multi-path redundant fiber optic cable network. The method includes: monitoring cable paths in the fiber optic cable network using distributed fiber optic sensing to detect cable break events; measuring cable break rates for the cable paths in the fiber optic cable network over a period of time based on the detected cable break events; determining availability of the fiber optic cable network over the period of time, the availability determined based on the number of redundant cable paths in the fiber optic cable network and the cable break rates of the cable paths; and providing an indication when the fiber optic cable network achieves a target availability with at least one less redundant cable path.

[0008] According to a second aspect of the present disclosure there is provided a method for reducing the number of redundant cable paths in an n-path redundant fiber optic cable network having a target availability, the method including: monitoring cable break-related events in the n cable paths in the fiber optic cable network in real-time using distributed fiber optic sensing; measuring cable break rates of the n cable paths over a period of time based on the monitored cable break-related events; computing availability of n-1 cable paths based on the measured cable break rates; and providing an indication when the fiber optic cable network achieves the target availability with the n-1 cable paths. Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

[0009] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 is a schematic of an example road cross-section showing various assets buried under the road.

[0011] Fig. 2 is a block diagram of an example system for reducing redundancy in a redundant multi path fiber optic network according to aspects of the present disclosure.

[0012] Fig. 3 illustrates an exemplary arrangement of a distributed fiber optic sensing (DFOS) system.

[0013] Fig. 4 is a flowchart illustrating an example method for performing distributed acoustic sensing in one or more optical fibers in a network.

[0014] Fig. 5 is a flowchart illustrating an example method for detecting excavation events in real time based on the distributed acoustic sensing.

[0015] Fig. 6 is a flowchart illustrating an example method for performing distributed acoustic sensing in one or more optical fibers in a network.

[0016] Fig. 7 is a flowchart illustrating an example method for detecting cable break events in cable paths in a multiple cable path network based on the distributed acoustic sensing.

[0017] Fig. 8 is a flowchart illustrating an example method for reducing redundancy in a multiple cable path network according to aspects of the present disclosure.DETAILED DESCRIPTION

[0018] As described previously, fiber optic cable disturbances, such as breaks / tears or movements, can have a number of adverse impacts both on the cable asset itself and on the underlying network of which the cable is a component. Adverse impacts include but are not limited to physical damage to the cable coatings or core, movement of the cable into a more vulnerable position, and loss of packets at the physical layer of the internet.

[0019] Cable disturbances can be caused by natural events like floods, fires, ground deformation and animal burrowing, or as discussed previously, by human activity like normal telecommunication network maintenance, construction activity, excavation in the vicinity of the optical cables, etc.

[0020] Generally speaking, a number of approaches have been deployed to mitigate the damage to underground fiber optic cables. One such approach requires excavation or construction parties to contact organizations such as “Before you dig” to determine what underground assets are located at a potential excavation site before beginning any excavation or construction operation, as well as their exact location. Excavation or construction can then proceed such that it avoids digging around any existing assets determined to be in the location. As will be appreciated, this approach is generally time consuming. The excavation / construction party has to first contact the organization, which then contacts each of the potential asset networks to determine if any assets are located in the potential excavation site and then provides this information back to the excavation / construction party. Otherwise, the construction party has to rely on existing network maps. This process can take time and because of the delays, some excavation / construction parties (rogue excavators) may proceed with excavating / construction before determining the location of any underground assets.

[0021] Another rudimentary approach is to use fiber optic technicians to patrol the length of any underground asset periodically and supervise excavation / construction activities. However, this approach also has issues as technicians cannot monitor the entire length of an optical cable continuously and rogue excavators / construction agents may begin excavation / construction when a technician is not patrolling an area.

[0022] Accordingly, existing techniques for preventing fiber damage are not adequate. Because of this, significant (at least fourfold) fiber optic cable redundancy is required to achieve a particular availability score and provide almost 100% uninterrupted data services to clients. The redundancy may be provided via a multi-node mesh network, where the nodes are connected to each other via one or more diverse fiber optic paths.

[0023] Aspects of the present disclosure address one or more of these issues. In particular, aspects of the present disclosure provide mechanisms to provide real-time detection of potential and actual threat events to fiber optic cable assets. As referred to herein cable threat events refer to human events (such as excavation, construction, explosion, etc.) that have the potential to cause damage to underground cable assets. Detection of these threat events are provided to a threat detection system that is coupled to an alert system, which contacts relevant parties and / or dispatches personnel to the site of the event to engage such parties before they can potentially damage any fiber optic cables.

[0024] By providing real-time monitoring, the claimed systems and methods increase field resource efficiency and effectiveness as the monitoring reduces the chances of missing cable threat events that happen in gaps in patrols, reduces the need for constant patrolling as field technicians are alerted when a potential cable threat event occurs, and has a deterrence effect that accumulates over time with rogue diggers / construction workers becoming aware they are being observed, and making the necessary enquiries through “Before you Dig” or other services.

[0025] Further, real time alerts can allow precision engagement with only the parties that are high risk to cause asset damage over time for efficient and effective cable break rate reductions. By providing such real-time information regarding potential cable threat events and generating alerts, aspects of the present disclosure effectively reduce the probability of cable damage over time, thus increasing the availability of the cable, and thereby ultimately allowing for reduction in redundancy of fiber optic cables or physical paths required in a network to service a given client.

[0026] Aspects of the present disclosure also monitor fiber optic cables over time to determine their break rates, i.e., the rate at which a given fiber optic cable breaks over a given period. The systems and methods then utilizes these determined cable break rates to compute the total availability of any given network that services clients. Based on the break rates and an availability required by the client, the systems and methods described herein can compute the redundancy required in any given network. The systems and methods may also be configured to facilitate manual removal or automatically cause removal of one or more cable routes / paths between client sites as the availability of existing optical paths in a network increases (due to the real time monitoring and alerting).

[0027] These and other aspects of the present disclosure will be described in detail in the following sections.Example system

[0028] Fig. 2 illustrates an example system 200 according to aspects of the present disclosure. The system 200 includes a real-time cable monitoring system 202, a threat detection system 204, an alert system 206, an analyzer 208, and a redundancy system 210.

[0029] The real-time monitoring system 202 senses activity in an optical network and communicates this to the threat detection system 204. The threat detection system 204 analysis the sensed activity and determines whether a potential or actual cable threat event is occurring.The threat detection system 204 may also determine a threat level of the potential or actual cable threat event. If a detected threat event exceeds a predetermined threshold, the threat detection system 204 generates an interdiction causing alert, indicating the type of threat, the location of the threat, etc., and communicates this to the alert system 206. The alert system 206 may be configured to communicate the alert to one or more interested parties - e.g., patrolling services and / or excavation parties, who can then visit the location of the threat and interact with the digging / construction party to prevent damage to the fiber optic cables. As used to herein, the term interdiction refers to an action performed to stop or prevent the threat event from proceeding further. Interdiction may include visiting the location of the threat event and interacting with the party that is causing the threat to stop the activity. It may also include sending messages to the party that is causing the threat (e.g., if the party is identifier and communication information for the party is available) and informing the identified party of the potential threat to the cable assets.

[0030] The analyzer 208 on the other hand may be configured to detect cable breaks and measure cable break rates over time. Further still, the analyzer 208 may be configured to calculate availability of any given fiber optic network based on the measured cable break rates and the availability of individual network paths. The analyzer 208 periodically also determines whether the current redundancy of the system is sufficient to provide the required availability or if it exceeds the required availability. If the analyzer 208 determines that the availability of a given fiber optic network is above the required availability of the network, the analyzer 208 may generate an indication of this and communicate it to the redundancy system. The redundancy system 210 in turn may automatically remove one or more redundant paths in the network or message a network operator / customer regarding the increased availability and suggest removal of one or more redundant paths to reduce the infrastructure costs and the costs to customers.

[0031] Each of these systems and their operations will be described in detail in the following sections.Cable monitoring system

[0032] The real-time monitoring system 202 makes use of fiber optic distributed fiber optic sensing (DFOS) to provide spatial and temporal monitoring data within a geographical area, such as a city, utilizing one or more optical fibers distributed across the geographical area. One such DFOS system is a distributed acoustic sensing (DAS) system that relies on the occurrence of anearby acoustic event that causes a corresponding local perturbation of refractive index along an optical fiber. The required proximity of the acoustic event depends on noise floor of the sensing equipment, the background noise, and the acoustic properties of the medium or media between the acoustic event and the optical fiber. Due to the perturbed refractive index, an optical interrogation signal transmitted along an optical fiber and then back scattered in a distributed manner (e.g., via Rayleigh scattering or other similar scattering phenomena) along the length of the fiber will manifest in fluctuations (e.g., in intensity and / or phase) over time in the reflected light. The magnitude of the fluctuations relates to the severity or proximity of the acoustic disturbance. The timing of the fluctuations along the distributed back-scattering time scale relates to the location of the acoustic event.

[0033] It will be appreciated that the term DAS refers to sensing a source that has an acoustic component. This acoustic component may translate to a vibrational or seismic component when travelling though the earth or a solid body before causing local perturbation in a buried fiber optic cable.

[0034] Reference to acoustic data in this disclosure should be read as including any propagating wave or signal that imparts a detectable change in the optical properties of the sensing optical fiber. These propagating signals detected in the system may include signal types in addition to acoustics such as seismic waves, vibrations, and slowly varying signals that induce for example localized strain changes in the optical fiber. The fundamental sensing mechanism in one of the preferred embodiments is a result of the stress-optic effect but there are other scattering mechanisms in the fiber that this disclosure may exploit such as the thermo-optic effect and magneto-optic effect.

[0035] Reference to acoustic data also needs to be read in context with optical data. The raw optical data in the preferred embodiment is a stream of repeating reflection sets from a series of optical pulses directed down the sensing fiber. These reflection sets are sampled at very high rates (in the order of gigabits per second) and are demodulated into a series of time windows that correspond to a physical location along the optical fiber. The data in these time windows is used to demodulate the integrated strain along the local length of the fiber at that time. The integrated strain contains signals such as acoustics, seismic, vibration and other signals that induce strain on the fiber. The integrated strain data from demodulation results in much smaller data rates than the optical data collected (in the order of megabits per second). The extent of the time windowbins is selectable and is done so based on compromises between spatial resolution of sensor channels, signal frequency range, dynamic range, and maximum length range of the system.

[0036] While the acoustic data is more efficient to store in terms of data set size, storing the optical data set allows for any one of the demodulation parameters to be changed and new demodulated data generated with a different set of selections for spatial resolution of sensor channels, signal frequency range, dynamic range, and maximum length range of the system.

[0037] In one example, the real-time cable monitoring system 202 is illustrated in Fig. 3. The cable monitoring system 202 includes a coherent optical time-domain reflectometer (C- OTDR) 302 or a phase optical time-domain reflectometer (cp-OTDR). The OTDR 302 includes a light source 304 to emit an optical interrogation field 306 in the form of a short optical pulse to be sent into each of optical fibers 305 A, 305B, and 305C. The optical fibers 305 A, 305B and 305C are distributed across a geographical area 307.

[0038] The C-OTDR 302 also includes a photodetector 308 configured to detect the reflected light 310 scattered in a distributed manner in the optical fibers and produce a corresponding electrical signal 312 with an amplitude proportional to the reflected optical intensity resolved over time. The time scale may be translated to a distance scale relative to the photodetector 308. An inset in Fig. 3 illustrates a schematic plot of such signal amplitude over distance at one particular instant.

[0039] In one arrangement, the optical fibers utilized to monitor the cables may form or be a part of a network of optical fibers. The network may be an established fiber-optic telecommunications network, in recognition of a scenario where fiber-optic communications networks are often installed with more communications capacity than required at the time of installation. In one form, the under-utilized communications capacity includes one or more unlit optical fibers. For example, a fiber-optic bundle may include multiple optical fibers, one or more of which are configured to carry communications information while the others remain unlit until the lit ones reaches capacity. These unlit optical fibers may therefore be borrowed or otherwise utilized for monitoring the cables according to aspects of the present disclosure. In another form, the extra communications capacity includes one or more unused spectral channels.

[0040] As an alternative or in addition time-domain-multiplexing of the C-OTDR function with a telecommunication function in the same spectral channel may be employed. The C-OTDR may be spectrally overlapped with telecommunication channels by synchronizingwhen the optical field (for the C-OTDR function this could be either discrete pulses or continuous optical fields in spread spectrum modulation techniques) sent or associated with the C-OTDR function and when it was associated with the Telecommunication function.

[0041] The one or more unused spectral channels may include wavelengths outside the wavelength range used in the optical fibers for communications purposes. For example, if all optical fibers in the fiber-optic bundle are lit, and the communications wavelengths in the optical fibers span the C band (between approximately 1530 nm and approximately 1563 nm) and the L band (between approximately 1575 nm and approximately 1610 nm) for communications purposes, one or more unused wavelengths at outside the C band or the L band nm may be utilized for obtaining acoustic information according to the present disclosure. The particular selection of the one or more unused wavelengths may be based on the gain spectrum of any existing erbium-doped fiber amplifiers (EDFAs) deployed in the communications network for extending its reach. Where existing EDFAs are deployed, selecting the one or more unused wavelengths from discrete wavelengths at 1525 nm, 1569 nm and 1615 nm (i.e. just outside the C and L bands) enables amplification without the need for additional EDFAs to extend the reach of interrogation signals. In another arrangement, the network may include a dedicated network for acoustic sensing purposes, operating in conjunction with an established network for fiberoptic communications, to extend the reach of acoustic sensing. The major advantage of using an existing communications network is that no dedicated cables have to be deployed at an additional and very significant cost.

[0042] The optical fibers are distributed across the geographical area to substantially cover public areas in the geographical area, in contrast to optical fiber deployment along a perimeter of the geographical area (e.g. surrounding a secure building or campus) or deployment covering in a substantially linear or elongate space (e.g. along a long gas or oil pipe). The distribution may be substantially even to cover the geographical area. Alternatively, the distribution may be denser to cover some portion(s) of the geographical area in higher spatial resolution than others, which is typically the case in inner city / urban areas, or other areas with high fiber optic coverage, as a result of the NBN network in Australia for example.

[0043] During operation, at multiple instants, interrogating optical signals or fields 306 are transmitted into each of one or more optical fibers (e.g. one or more of 305A, 305B and 305C) distributed across the geographical area (e.g. 307), which is typically an urban environment. Theoptical fibers typically form part of a public optical fiber telecommunications network, which provides a high degree of coverage (practically ubiquitous) in an urban and particularly inner- city environment. During an observation period following each of the multiple instants, the COTDR 302 receives returning optical signals (e.g., 310) scattered in a distributed manner over distance along the one or more of optical fibers (e.g. one or more of 305A, 305B and 305C).

[0044] This configuration permits determination of an acoustic signal (amplitude, frequency and phase) at every distance along the fiber-optic sensing cable. In one embodiment, the photodetector / receiver 308 records the arrival times of the pulses of reflected light in order to determine the location and therefore the channel where the reflected light was generated along the fiber-optic sensing cable. This phased array processing may permit improved signal-to-noise ratios in order to obtain improved detection of an acoustic source, as well as the properties of the acoustic source.Threat detection system

[0045] The output from the photodetector 308 may be provided to the threat detection system 204, which is configured to process acoustic fluctuations 316 in the electrical signal 312 and determine whether a potential threat event is occurring and to determine a location of the potential threat event from the processed acoustic fluctuations.

[0046] These acoustic fluctuations are acoustic signals that contain a number of different acoustic frequencies at any one point and along a series of different spatial points that the threat detection system 204 converts to a digital representation of the nature and movement of the sound targets around the cable grid. In contrast to scalar measurands such as temperature (which typically don’t provide any dynamic information above a few Hz), acoustic signals contain a significant number of frequency components (up to many kHz, which are unique and distinguishable to a specific target type) and vector information, i.e., the amplitude information derived from the Fourier domain (of single channels) and the multi-channel time domain (spatial information) such as direction of the “target” and the spatial position for facilitating GIS overlay and velocity parameters (speed and acceleration).

[0047] The digitized electrical signal 312, any measured fluctuations 316, and / or processed data associated therewith may be stored in a storage unit (not shown). The storage unit may include volatile memory, such as random-access memory (RAM) for the threat detection system 204 to execute instructions, calculate, compute, or otherwise process data. The storage unit mayinclude non-volatile memory, such as one or more hard disk drives for the threat detection system 204 to store data before or after signal processing and / or for later retrieval. The threat detection system 204 and storage unit and may be distributed across numerous physical units and may include remote storage and potentially remote processing, such as cloud storage, and cloud processing, in which case the threat detection system 204 and storage unit may be more generally defined as a cloud computing service.

[0048] During operation, once the photodetector 308 receives the backscattered signals 310, converts these to electrical signals, and communicates them to the threat detection system 204, the threat detection system 204 demodulates the received electrical signals to separate the acoustic data associated with acoustic disturbances caused by the multiple targets from the optical signals 310 detected within the observation period.

[0049] In some embodiments, the threat detection system 204 may apply acoustic signaturebased filters to the acoustic data to detect threat objects / events. These filters could be in the form of software-based FIR (finite impulse response) or correlation filters, or classification could alternatively be implemented using big data and machine learning methodologies. This latter approach would be applicable where higher levels of discrimination of sound objects is required, such as details of vehicle type or sub-class or sub-classes of other objects.

[0050] In some embodiments, the threat detection system 204 generates symbols representative of threat objects and / or threat events and stores these in the digital symbol index database. Each symbol index includes an event / object identifier with time and location stamp). Event / object identifiers could include excavators, jackhammers, borers, mechanical diggers, manual digging, and the like. The series of different software-based correlation filters is provided for each classification type above (each correlation filter is tuned to particular characteristics in the acoustic time series and acoustic frequency domain) and once the output of one of these software-based filters reaches a threshold, a threat detection and classification event is triggered in the threat detection system 204. The system 204 now has a digital representation of a potential threat event with properties such as what type of threat event it is, where the event is located geographically, how fast a threat object such as a digger or borer is moving and a host of other properties that can be deduced from the acoustic data associated with this cable threat event.

[0051] In addition, the threat detection system 204 may determine a threat level based on the determined event(s). In some embodiments, the threat detection system 204 may store alert criteria with the symbol index database, with each symbol having at least one associated alert criterion (threshold amplitude / frequency). The alert criteria may form part of a semantics or context engine in the threat detection system 204, which processes a number of factors, which can be used to determine the level of threat or danger associated with an event, and thereby deliver actionable information.

[0052] For example, in the case of an excavator, the speed and direction of movement of the excavator may be factored in to determine a threat level - if the excavator is moving closer to a known cable location or is moving toward it at a speed higher than a threshold speed, a high threat level may be associated with the threat.

[0053] Other information identified by the threat detection system 204, such as the identity of the relevant party, e.g., the excavator / entity performing the works, can be used to generate targeted alerts to the entity in the event an excavation / construction operation has the potential of damaging or severing the cable. In addition, if the threat event was associated with a known and reliable party, e.g., a reputed contractor then this could be factored into the decision making process when determining a threat level.

[0054] In other cases, the threat detection system 204 may retrieve information relating to the location of all public works being conducted in the geographic area. If a cable threat event is detected, the threat detection system 204 may compare the location of the threat event with the locations of all authorized public works in that location. If no public works are authorized to be performed in the location of the detected threat event, a high threat level may be assigned to the event. Alternatively, if the threat event location matches a location of an authorized public work, the threat detection system 204 may assign a lower threat level to the event.

[0055] If a threat is detected by the threat detection system and / or the threat level exceeds a threshold, the threat detection system 204 may generate an interdiction causing alert and communicate this to the alert system 206.Alert system

[0056] Upon receiving an alert from the threat detection system 204, the alert system 206 is configured to communicate the alert to one or more relevant parties. For example, the alert system 206 may communicate the alert (including the threat level and / or location of the potentialthreat event) to patrolling technicians, to the threat party (if identified), and / or to any other authorities that may assist in controlling the threat event. The relevant party may then take intervening steps to stop the threatening activity and / or to alert the relevant party of the cable assets in the vicinity of the threatening event such that the relevant party can avoid digging in the general area of the cable assets.

[0057] Threat levels may be indicated in the alerts both graphically using say a familiar green, orange, and red color scheme, flashing symbols and / or audibly using audible alarms of progressively increasing volume.Threat detection method

[0058] Figs. 4 and 5 are flowcharts illustrating example methods 400 and 500 for detecting a threat event in an optical fiber. In particular, method 400 is performed to retrieve data for processing and method 500 is performed on the retrieved data to determine whether a threat event has occurred. It will be appreciated that these methods are described with reference to one optical fiber for simplicity. In actual implementation, the methods are performed for detecting threat events in multiple optical fibers in the same or different geographical locations and therefore these methods are repeated simultaneously and / or serially for different optical fibers. It will further be appreciated that in the case of a cable comprising a bundle of optical fibers a single fiber in the bundle will be configured as a DAS fiber to sense fiber breakage.

[0059] The method 400 commences at step 402, where an optical interrogation field 306 in the form of a short optical pulses is transmitted from a DFOS system 202 into the optical fiber (e.g., optical fiber 305A).

[0060] At step 404, reflected and / or backscattered signals are received at the DFOS system and in particular at the photodetector 308.

[0061] The photodetector detects the reflected light 310 scattered in a distributed manner in the optical fibers and produces a corresponding electrical signal 312 with an amplitude proportional to the reflected optical intensity resolved over time at step 406. The photodetector 308 may also record the arrival times of the pulses of reflected light in order to determine the location and therefore the channel where the reflected light was generated along the optical fiber 305A at this step.

[0062] It will be appreciated that method 400 may be performed periodically or continuously. Method 500 may also be performed periodically or continuously. However, the periodicity of method 500 may be different from the periodicity of method 400. For example, method 400 may be performed every few seconds, whereas method 500 may be performed at a slower cadence, e.g., every minute, or every few minutes, or even hours.

[0063] If the periodicity of the methods is out of synchronization, the electrical signals 312 output by the photodetector 308 may be stored in a database at the end of step 406 and retrieved from the database by the threat detection system 204 when it is ready to process the data. Alternatively, when the periodicity of the methods is in synchronization, the electrical signals output by the photodetector 308 may be communicated directly to the threat detection system 204 for processing method 500.

[0064] In any event, method 500 commences at step 502, where acoustic related fluctuations 316 in an electrical signal 312 are processed to determine whether a potential threat event is occurring. In some embodiments, the photodetector 308 communicates the electrical signals to the threat detection system 204 to do this and in other embodiments, the threat detection system 204 retrieves the electrical signals 312 corresponding to a period of time since the last time step 407 was performed.

[0065] In particular, the threat detection system 204 demodulates the received or retrieved electrical signals 312 to separate the acoustic data associated with acoustic disturbances 316 caused by the multiple targets from the optical signals 310 detected within the observation period.

[0066] In some embodiments, the threat detection system 204 applies acoustic signaturebased filters (related to threat events and / or threat objects) to the acoustic data to detect threat objects / events as described previously. If the acoustic fluctuations exceed a threshold of any of the signature-based filters, the threat detection system 204 may determine that a threat event has occurred or is occurring. Alternatively, if the acoustic fluctuations do not exceed the threshold of any one of the signature-based filters, the threat detection system 204 may determine that no threat event has occurred.

[0067] If at step 504, it is determined that a potential threat event is not occurring, the method ends.

[0068] Alternatively, if a threat event is detected at step 504, the threat detection system 204 determines the location of the threat event at step 506. This may be determined based on the arrival of time of the pulses that correspond to the acoustic fluctuations that exceeded the one or more signature filters.

[0069] At step 508, the threat detection system 204 assigns a threat level to the detected threat event as described previously.

[0070] Next, at step 510, a determination is made whether the assigned threat level exceeds a threshold. For example, threat levels in the range of 1-5 may be assigned to a threat event, where a threat level of 1 is assigned if the threat event is detected at least a threshold distance away from the fiber optic cable asset and / or if the direction of threat is detected to be in a direction away from the cable asset. Alternatively, a threat level of five may be assigned if the threat event is detected very close to the cable asset or is detected to proceed in the direction of a cable asset at a certain speed. It will be appreciated that this is merely an example, and any other scoring or ranking technique or system may be employed (with different number of levels, different level names, etc.) without departing from the scope of the present disclosure.

[0071] If at step 510 a determination is made that the assigned threat level exceeds a threshold (e.g., a preconfigured threshold threat level, such as threat level 2, 3, or 4), the method proceeds to step 512, where the threat detection system 204 generates an alert and communicates this to the alert system 206. Alternatively, if the threat level does not exceed a threshold, the method returns to step 502, where the threat detection system 204 analyzes electrical signals 312 corresponding to a next period of time to determine whether a threat event is occurring.

[0072] The method also returns to step 502 after step 512 so that the electrical signals corresponding to the next period of time can be analyzed.Analyzer

[0073] In addition to detecting threat events and generating alerts, the system 200 also determines fiber break rates and availability of the optical fibers. To this end, the analyzer 208 receives electrical signals 312 from the cable monitoring system 202 and stores these in a database. It then periodically analyses the electrical signals 312 to determine whether any cable break events are detected. Cable break events may occur where a cable has been damaged or destroyed and can no longer reliably communicate data. A cable break event may be detected using any known DAS or DFOS disturbance detection system. In one example, the cable breakevent may be detected using the disturbance detection technique described in co-pending PCT Application no. PCT / AU2024 / 050091, titled, “Systems and methods for detecting disturbance events in optical fibers” having a priority date of 14 February 2023, the entire contents of which are incorporated herein by reference.

[0074] As disclosed in that US patent application, cable breaks can be detected based on electrical signals output by the cable monitoring system 202. In particular, the analyzer 208 may measure the optical phase of backscattered light along a length of fiber optic cable using a phasesensitive optical time domain reflectometer (cp-OTDR) that measures the phase evolution of the backscattered signals along an optical fiber. The analyzer 208 can then differentiate the measured phase in both time and space. In some embodiments, if a threshold number of the differentiated phase signals fall within predetermined phase ranges, the system can determine that a cable break event has occurred. Otherwise, it may determine that no cable break events have occurred. In other embodiments, a histogram can be charted based on the spatial and temporal phase differentials. The shape of the histogram can then be analyzed to detect existence or otherwise of a cable break event. For example, if the histogram has a particular probability distribution or shape (e.g., flat), the system can determine that a cable break event has occurred. Alternatively, if the histogram has a different shape, e.g., bell-shape, the system can determine that a cable break event has not occurred. Further, by measuring both the spatial and temporal phase differentials, the analyzer 208 detects not only that a cable break has occurred but also the precise location of that break along a fiber optic cable.

[0075] Whenever a cable break event is detected, the analyzer 208 may record the cable break event along with information about the cable, e.g., the location of the break, a unique identifier of the optical cable, the network the cable belonged to, as well as the duration of the break event until it is repaired, etc.

[0076] Over time, doing so, the analyzer 208 can determine the current cable break rate for any given fiber optic network (e.g., based on the number of cable break events recorded for that fiber optic network in a given period of time, as well as the duration of such events) and also to determine a trend in the cable break rate year on year (e.g., based on the cable break rates for each year). As used herein, cable break rate refers to the rate at which a cable breaks over a period of time (e.g., a year), together with the duration of such breaks. If a cable breaks four times in a year, the respective breaks taking 72, 60, 52 and 24 hours to repair, the total outagetime is 208 hours and the cable break rate is 8.6666 / 365 = 2.374% for that year. For example, the analyzer 208 may determine that for a given cable path, the cable break rate for a first period (e.g., first year) was 2.374% and for a second annual period was 1.234%. Based on data for a few more periods, the analyzer 208 can determine a trend in the cable break rate.

[0077] Further still, the analyzer 208 may determine the availability of individual cable paths and of individual networks based on the cable break rate. The cable availability and network availability refers to the amount of time the cable or network was available for data transmission in a year and it can be represented as 1 — cable break rate. For example, if a cable’s break rate related down time is 2.374%, its availability may be 97.626% and if the cable’s break rate related downtime is 1.234%, its availability may be 98.766%.

[0078] From the availability of individual cables, the availability of a network (i.e., the average availability of all the optical cable paths that make up a given network for a client) can be determined. For example, when a network involves n redundant paths (such as diverse routes in a cloud network), the effective availability of the network is computed as full availability (100%) minus the product of the availability of individual paths as -Availability = 1 — [(1 — Avail^ x (1 — Avail X ... x (1 — Avail^]

[0079] For an example network that includes 3 optical paths, where each path has an individual availability of 96.3%, the availability of the network is -1 - [(1 - 96.3%) X (1 - 96.3%) X (1 - 96.3%)] = 99.995%

[0080] Using the availability equation above, the analyzer 208 determines the network availability with different number of redundant paths at different intervals. Table A below illustrates an example calculation performed by the system 208. In this example table, the definition of availability of the network is assumed to be at the physical layer. This definition is applied consistently to the overall network availability and the individual path availability.

[0081] The table A illustrates the availability of a four-path network that has a target availability of 99.995%. The availability at time TO is computed for the network if it has 1 path, 2 paths, 3 paths and 4 paths and is depicted in the second column. This shows that the individual path availability needs to be at 91.6% for the overall network availability target of 99.995%. The cable break rate is then computed at different points in time for particular periods. In this example, the cable break rate reduces at each interval in comparison to the previous interval. As can be seen from the table, this causes an increase in the availability of the individual cables and in turn of the network. As can be seen from the table, the network achieves the availability target of 99.995% with three routes at the interval T3 and with two routes at the interval T6.

[0082] Accordingly, at time T3, the analyzer 208 can generate a message to reduce the redundancy in the network from four paths to three paths and communicate this message to the redundancy system 210. The redundancy system 210 receives this message and either automatically removes one redundant path from the network or alerts a network operator to consider removing a redundant path from that network. The message may include the computed network availability with lesser paths along with identifiers of the network and the individual cables.

[0083] Similarly, at time T7, the analyzer 208 may generate another message to further reduce the redundancy of the network from three paths to two paths and communicate this message to the redundancy system 210. In turn, the redundancy system 210 receives this message and either automatically removes a further redundant path from the network or alerts a network operator to consider removing another redundant path from that network.

[0084] Table B below illustrates another example availability calculation performed by the system 208 for a network including three paths and having the same availability requirements.

[0085] The availability at time TO is determined for the network if it has 1 path, 2 paths, and 3 paths and depicted in the second column. This shows that the individual path availability needs to be at 96.32% for the overall network availability target of 99.995%. The cable break rate is then computed at different points in time for particular periods. In this example, the cable break rate reduces at each interval in comparison to the previous interval. As can be seen from the table, this causes an increase in the availability of the individual cables and in turn of the network. As can be seen from the table, the network achieves the availability target of 99.995% with two routes at the interval T5.

[0086] Accordingly, at time T5, the analyzer 208 can generate a message to reduce the redundancy in the network from three paths to two paths and communicate this message to the redundancy system 210. The redundancy system 210 receives this message and either automatically removes one redundant path from the network or alerts a network operator to consider removing a redundant path from that network. The message may include the computed network availability with lesser paths along with identifiers of the network and the individual cables.

[0087] It will be appreciated that a network between two client sites / a data center and a client site A and D may in one example include four separate paths between A and D and in another example may include multiple nodes (e.g., nodes B and C) between the sites with subpaths ABCD, ABD, and ACD. It will be appreciated that calculations around network redundancy will depend on network topology including number of paths, nodes, and sub-paths.

[0088] This way, by monitoring cable breaks, computing cable break rates, and cable availabilities, aspects of the present disclosure can reduce redundancy in optical cable networks, with an associated reduction in infrastructure costs. Advantages may include a reduction in infrastructure costs, and / or the ability of the network to carry increased traffic, between client sites / data centers as redundancy decreases.Analyzing method

[0089] Figs. 6, 7 and 8 are flowcharts illustrating example methods for reducing the redundancy in a fiber optic cable network. In particular, method 600 is performed to retrieve optical data for detecting cable breaks, method 700 is performed to detect cable breaks and method 800 is performed to determine whether the redundancy in an optical network can be reduced. Method 700 requires the output of method 600 to detect cable breaks and method 800 requires the output of method 700 to determine the redundancy.

[0090] Method 600 commences at step 602, where an optical interrogation field 306 in the form of a short optical pulses is transmitted from a DFOS system 202 (e.g., an cp-OTDR system) into optical fibers in each of the cable paths of an optical fiber network (e.g., optical fiber 305A, optical fiber 305B, 305C).

[0091] As described herein, an optical fiber network may be made up of hundreds if not thousands of optical fibers. Some of these optical fibers may be bundled together to form an optical cable. Further, two nodes in an optical network may be connected via two or more optical cables forming different cable paths. This way, network redundancy may be provided between any two nodes in a network. The number of cable paths provided between different nodes may depend on the availability target of an operator or the availability target of a customer. For example, an operator may have a 100% availability target and therefore may have many different cable paths between any two connected nodes in the network. On the other hand, a customer may only have an availability requirement of 98%. In this case, the number of cable paths allocated to the customer may be fewer in number.

[0092] In the example method described herein, the optical network includes a number of cable paths and network nodes between two locations of a customer’s premises. The number of cable paths allocated to the customer depend on the customer’s availability target and the break rate / availability of the cable paths in the network. The number of optical fibers within the cable path allocated to a customer depends on the bandwidth requirement of the customer.

[0093] At step 604, reflected and / or backscattered signals are received from each of the cable paths in the optical network at the DFOS system and in particular at the photodetector 308.

[0094] At step 606, the photodetector 308 detects the reflected light 310 scattered in a distributed manner in the optical fibers 305 and produces corresponding electrical signals 312 with amplitudes proportional to the reflected optical intensity resolved over time. Thephotodetector 308 may also record the arrival times of the pulses of reflected light in order to determine the location and therefore the channels where the reflected light was generated along the optical fibers.

[0095] It will be appreciated that method 600 may be performed periodically or continuously. Method 700 (that utilizes the output of method 600) may also be performed periodically or continuously. However, the periodicity of method 700 may be different from the periodicity of method 600 in some embodiments. For example, method 600 may be performed every few seconds, whereas method 700 may be performed at a slower cadence, e.g., every day, every week, every month, or even every year.

[0096] If the periodicity of the methods is out of synchronization, the electrical signals output by the photodetector 308 may be stored in a database and retrieved from the database by the analyzer 208 when it is ready to perform method 700. Alternatively, when the periodicity of the methods is in synchronization, the electrical signals output by the photodetector 308 may be communicated directly to the analyzer 208 and the analyzer may immediately perform method 700.

[0097] In any event, method 700 commences at step 702, where the analyzer 208 receives or retrieves electrical signals for a given period, depending on the periodicity of method 700, and analyzes these electrical signals to determine whether any cable break events are detected in any of the cable paths.

[0098] In one example, the analyzer 208 measures the optical phase of the electrical signals. The analyzer 208 can then differentiate the measured phase in both time and space. In some embodiments, if a threshold number of the differentiated phase signals fall within predetermined phase ranges, the analyzer 208 determines that a cable break event has occurred in a given cable path. Otherwise, it may determine that no cable break events have occurred. In other embodiments, a histogram can be charted based on the spatial and temporal phase differentials. If the histogram has a particular probability distribution (e.g., flat), the analyzer 208 can determine that a cable break event has occurred. Further, by measuring both the spatial and temporal phase differentials, the analyzer 208 detects not only that a cable break has occurred but also the precise location of that break along an optical fiber.

[0099] If at step 704 a cable break event is detected, the analyzer 208 may record the cable break event along with information about the break, e.g., the location of the break, a uniqueidentifier of the optical cable path, the network the cable belonged to, as well as the duration of the break event until it is repaired, etc., at step 706.

[0100] Alternatively, if a cable break event is not detected (no path from step 704), no data may be recorded for that period of time and method 700 ends for that iteration.

[0101] It will be appreciated that method 700 is repeated based on a preselected but configurable interval (e.g., weekly, monthly, quarterly, yearly, etc.) to update the record of cable breaks in the optical fiber network.

[0102] Method 800 may be performed at the same interval as method 700 or at a different interval. In some embodiments, method 800 may be repeated, e.g., every six months or every year. Method 800 commences at step 802 where the analyzer 208 analyzes the recorded cable break events associated with each cable path to determine its cable break rate. This is done on a cable path basis by identifying the cable break event records related to a given cable path (e.g., by performing a lookup in the database using the cable path identifier) for a given interval (e.g., all cable break events in the last year). From each of the identified records, the analyzer may also determine the duration of the corresponding break event. This downtime from all the identified records for a given cable path and interval is combined to determine the cable break rate for that interval.

[0103] The analyzer may also determine the break rate for the entire network. This can be done by multiplying the cable break rates of each of the cable paths.

[0104] Next, at step 804, the analyzer 208 determines the availability of the individual cable paths and of the network based on the cable break rates. The cable availability and network availability is determined based on the following equations -Cable availability (CAvail) = 1 — cable break rateNetwork availability = 1 — [(1 — CAvall^ x (1 — CAvalL^) x ... x (1 — CAvail^]

[0105] Once the cable and network availability is determined, the method proceeds to step 806, where a determination is made whether the network availability exceeds the availability target for the customer. If the network availability does not exceed the availability target for the customer, the method ends.

[0106] Alternatively, if the computed network availability exceeds the availability target for the customer, the method proceeds to step 808, where the analyzer 208 determines the networkavailability with different combinations of a reduced number of cable paths. For example, if the network has 4 cable paths (A, B, C, and D), the analyzer 208 may determine the network availability when different combinations of three cable paths are selected (e.g., combination A, B, C or combination, A, C, D, or combination B, C, D, etc.).

[0107] The analyzer 208 then determines at step 810 whether the network availability computed for any of the combinations of reduced number of cable paths is equal to or greater than the availability target. If a determination is made that one or more combinations lead to a network availability that is equal to or greater than the availability target, the analyzer 208 records these combinations. Further, if at least one combination is determined that exceeds the availability target, the analyzer may further reduce the number of cable paths by 1 and recalculate the network availability with different combinations of the reduced number of cable paths (e.g., combination of A and B, combination of B and C, combination of A and D, etc.). This may proceed until the analyzer determines the lowest number of optical paths required to maintain the target availability.

[0108] If at step 810, the network availability for any reduced combinations of cable paths is determined to equal or exceed the network availability target, the analyzer 208 records these cable path combinations and the method proceeds to step 812, where the analyzer 208 generates a message indicating that it is possible to reduce the redundancy in the network and still meet the current availability target. The message may include the identifier of the cable paths that can be kept, the identifier of the one or more cable paths that can be removed (e.g., the cable paths with the lowest availability rate), and the computed network availability with the reduced number of cable paths.

[0109] The message may then be communicated to the redundancy system 210. The redundancy system 210 can receive this message and either automatically remove one or more of the redundant paths mentioned in the message from the optical network or alert a network operator or customer to consider removing a redundant path(s) from that optical network.

[0110] Alternatively, if at step 810, a determination is made that the availability calculated for none of the combinations of reduced number of cable paths is equal to or greater than the target availability, the method end.

[0111] It will be appreciated that method 800 describes one way of computing the availability. In other embodiments, instead, of determining the availability based on all existingcable paths first, the analyzer 208 may determine the availability based on all combinations of different number of cable paths in an ascending order (e.g., as shown in tables A and B). Accordingly, in such embodiments, method steps 804 and 806 may be omitted. Instead, steps 808 and 810 may be performed to determine availability based on ascending number of cable paths (e.g., two cable paths first, then three, then four) and the computation may be halted when a combination of cable paths is identified for which the availability is equal to or greater than the target availability.

[0112] Further, it will be appreciated that in some embodiments, the cable break rates for two or more cable paths in a network may be identical. In such cases, it is not necessary to calculate the availability for all combinations of cable paths as some of the computed availabilities will be the same.

[0113] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

[0114] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers, or steps.

Claims

CLAIMS1. A method for reducing a number of redundant cable paths in a multi-path redundant fiber optic cable network, the method including: monitoring cable paths in the fiber optic cable network using distributed fiber optic sensing to detect cable break events; measuring cable break rates for the cable paths in the fiber optic cable network over a period of time based on the detected cable break events; determining availability of the fiber optic cable network over the period of time, the availability determined based on the number of redundant cable paths in the fiber optic cable network and the cable break rates for the cable paths in the fiber optic cable network; and providing an indication when the fiber optic cable network achieves a target availability with at least one less redundant cable path.

2. The method of claim 1, further comprising: removing at least one redundant cable path from the fiber optic cable network in response to the indication.

3. The method of claim 1 further including installing at least one DFOS system to monitor the cable paths of the fiber optic cable network.

4. The method of claim 3, wherein monitoring the cable paths of the fiber optic cable network includes: repeatedly transmitting, at multiple instants, interrogating optical signals into at least one optical fiber associated with each cable path of the fiber optic cable network; and receiving, during an observation period following each of the multiple instants, returning optical signals scattered in a distributed manner over distance along the cable paths, the scattering influenced by acoustic disturbances caused by the multiple targets within the observation period.

5. The method of claim 4, further comprising determining a cable break by: determining a probability of occurrence of predetermined phase difference values between successive samples of processed backscattered signals from the cables.

6. The method of claim 5, wherein determining the probability of occurrence of the predetermined phase difference values between successive samples comprises generating a histogram of the phase difference values between successive samples and analyzing a shape of the histogram to detect existence or otherwise of a cable break event.

7. The method of claim 6, further comprising determining a cable break event if the histogram has a substantially flat shape.

8. The method of claim 4, further comprising determining the cable break event upon determining that disturbance events are detected in multiple consecutive locations along the optical fiber.

9. The method of claim 4, further comprising determining the cable break event upon determining that disturbance events are detected in all locations along the optical fiber downstream from an originating location.

10. The method of claim 1, wherein determining availability of the fiber optic cable network over the period of time comprises computing a full availability of the network minus a product of availability of individual cable paths of the network as -Availability = 1 — [(1 — Avail^ x (1 — Avail2) X ... x (1 — Avail^] where n is the number of cable paths in the network and availn represents the availability of the nthpath in the network and is computed as 1 -cable break rate of the nthpath.

11. The method of any one of the preceding claims wherein the fiber optic cable network is a telecommunications data network extending between at least two sites, which may include virtual private cloud sites.

12. The method of any one of claims 4-11 further comprising: analyzing the returning optical signals associated with a period of time to determine whether a cable threat event is occurring in real time; and generating an interdiction causing alert upon determining that the cable threat event is occurring.

13. The method of claim 12 further comprising: upon determining that the threat event is occurring: determining a location of the threat event; and assigning a threat level to the threat event depending at least on proximity of the threat event to an underground cable asset.

14. The method of claim 13, wherein the interdiction causing alert is generated when the assigned threat level exceeds a threshold threat level.

15. The method of any one of claims 12-14, wherein determining that the threat event is occurring and generating the interdiction causing alert results in a reduction in the cable break events over time through interdiction of the threat event.

16. A method for reducing the number of redundant cable paths in an n-path redundant fiber optic cable network having a target availability, the method including: monitoring cable break-related events in the n cable paths in the fiber optic cable network in real-time using distributed fiber optic sensing; measuring cable break rates of the n cable paths over a period of time based on the monitored cable break-related events; computing availability of n-1 cable paths based on the measured cable break rates; and providing an indication when the fiber optic cable network achieves the target availability with the n-1 cable paths.

17. The method of claim 16, further comprising: removing at least one redundant cable path from the fiber optic cable network in response to the indication.

18. The method of claim 16 or 17 further including installing at least one DFOS system to monitor the cable paths of the fiber optic cable network.

19. The method of claim 18, further comprising monitoring at least one of the n cable paths using the DFOS system to detect one or more threat events in real time and generate interdiction causing alerts in response to detecting the one or more threat events.

20. The method of claim 18, further comprising achieving a reduction in the cable break rate in the at least one cable path in the fiber optic cable network over time as a result of generating the interdiction causing alerts and through interdiction of the threat event.

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