Optical fibers have been around for quite some time, but as communication networks continue to follow Moore’s Law (an observation that the capacity of networks doubles every two years), telecommunications operators continue to rely on these small strands of glass wrapped in cable casing to build their network ecosystems.

These cables are so widespread that they span streets, cities, regions, countries and continents. And they cause operators to lose sleep because anything can happen to them, anywhere, and at any time! Deploying optical cables requires a large, CAPEX-intensive investment. In today’s inflationary market, operators are especially sensitive to any potential impact on this infrastructure asset because it could significantly impact their financial health. It’s no wonder many network operators are looking for ways to use automation to monitor, detect and locate disruptions or anomalies in their optical networks.

Optical fiber networks play a crucial business role for network operators by delivering communications capabilities that connect the entire world. Building resiliency into the design of the optical network is an integral part of the financial investment and strategy of all network operators because it ensures they can continue to adhere to their end-subscriber service-level agreements (SLAs).

Sleep easy with Nokia WaveSuite network automation

As you make these investments in your optical network, you continue to face the risk of service disruptions caused by fiber cuts. You may also face disruptions caused by other types of events beyond your control, including

• Intrusion in the form of eavesdropping, or tapping, on the fiber plant—­a security breach that puts your business at risk

• Maintenance activities by network operations teams or contract services assigned to repair fiber damage, bad splices, and dirty or bad connectors within the data center or on optical system equipment

• Environmental influences such as natural disasters or weather.

Let’s explore what’s available to help you detect what is really occurring on your optical fiber, metrics you can use to quantify the operational and business importance of a given event, and how you can use network automation powered by Nokia WaveSuite to seamlessly detect these events within the infrastructure layer of your optical network.

Disruption monitoring method for optical fibers

Operators commonly detect events on optical fibers with a mature monitoring technique executed using optical time-domain reflectometry (OTDR). This technique involves using a measurement from an out-of-band optical wavelength from the conventional DWDM spectral range to non-intrusively detect and locate anomalously lossy sections of fiber and other defects from one end of the fiber. The anomalies could be caused by intrusion events, maintenance activities or macro bends or breaks because of environmental influences.

The principles of OTDR monitoring stem from the physics of Rayleigh backscattering—light reflections back to the source resulting from imperfections—in optical fibers. The technique uses a time-of-flight method to determine the time light takes to travel a distance through the fiber from where the reflection occurred. In other words, the imperfection in the fiber will cause the light traveling down it to reflect at each of the problem incidences. By knowing the speed of light within the fiber, you can use it to compute the distance and locate the origin of the anomaly.

The Nokia 1830 Photonic Service Switch (PSS) provides OTDR instrumentation equipment that can be coupled with your optical line system equipment using integrated filters. With the PSS, you can inject a signal from either end of a fiber and configure the OTDR equipment to execute fiber scans and measure various cable lengths. OTDR provides real-time visibility into your network's health, allowing you to respond to problems promptly and restore services efficiently, before service disruptions escalate.

Nokia WaveSuite applications allows you to visualize the refection intensities from an OTDR trace across each span to identify the locations of potential faults within the network. Figure 1 shows a trace provided by the WaveSuite OTDR viewer with a measure of reflection (dB) on the y-axis and distance (km) on the x-axis. The graph provides a summary of the total loss on the fiber and marks locations on the graph to reference areas of interest and the measured distance to each of these locations.

Figure 1. WaveSuite OTDR visualization graph

Operational business performance indicators

One of the key performance indicators for your business success is your ability to repair the optical network when disruptive events occur. Many operators use mean time to repair (MTTR) as a baseline statistic for operational efficiency. MTTR is a measure of how quickly your business is handling and resolving unplanned network related faults, which impacts your downtime costs.

Keeping MTTR as low as possible ensures that your internal processes, skilled resources, supply chain and warehouse inventories are adequate to keep repairs on time. This efficiency ensures your transport network remains fully operational and adheres to end-subscriber SLAs, which reduces your risk of lost revenue.

A variety of factors can influence MTTR, including:

• Fiber duct types: aerial, underground or submarine cable

• Location of the failure: city areas with limited access points, inside the datacenter, remote hut locations or areas where the texture of the soil can be tough on buried cables

• Type of damage: fiber cut or break caused by construction equipment, urban rodents or aging or defective equipment connectors

• Completion time: often described in SLAs through service availability (uptime / {uptime + downtime})

Using automation to detect fiber events

The expression “looking for a needle in a haystack” is relevant to optical networks when events other than fiber cuts cause performance degradations. It often takes rigorous fault analysis to identify the source of these problems. If you have gone through this, you will know the process is onerous and time-consuming and can increase MTTR. The challenge is to streamline this process so you can quickly locate the problem and dispatch maintenance crews to resolve the issue.

WaveSuite applications provide real-time network performance information and insights to help you identify issues that can degrade the available margin on an optical segment and affect end-customer services. They enable you to identify fiber cuts or spans with excessive loss based on threshold alarms caused by unexpected degradations or intrusion. Whether the use case is troubleshooting, security or preventive maintenance, WaveSuite can detect, analyze and provide a report on the problem within a few minutes to help you minimize MTTR and make your business operations more efficient.

In one of our automation series blog posts, “Building automated closed-loop operations in your optical network”, we discuss automated optimization capabilities that can sense and detect reduced system margins relating to stress on the outside plant fiber, aging equipment or extreme environmental factors. While these capabilities are best used to mitigate reduced performance that does not immediately cause a service disruption, they do ensure you can develop proactive measures to mitigate failures before they occur. This translates to lower MTTR.

The WaveSuite advanced diagnostics (WS-AD) application enables you to automate troubleshooting and rapidly identify the root cause of failures. It helps you resolve potential network issues quickly by providing a means to accelerate the development of an actionable list of repairs for addressing the faults where they exist.

WS-AD also has a built-in troubleshooting workflow that can automatically trigger OTDR measurements on the network fiber spans that are experiencing failures. You can also use WS-AD to pre-schedule a network scan and have it automatically compare the current measurement with the system baseline to identify discrepancies from past operational conditions.

The application works with active (carrying traffic) and dark fiber deployments to ensure that all use cases are supported. It provides a pre-built workflow (Figure 2) that automatically generates a report showing a summary of the impacted connections and the locations on the fiber segments where the issue occurred. Through auto-triggered scans, WS-AD can execute a comparative summary against a network baseline scan to provide details on the impairment and allow operators to better plan their list of actions for repair. This helps you troubleshoot and isolate fault locations faster.

Figure 2. Automated intrusion detection and event reporting

WS-AD also enhances troubleshooting with capabilities that let you visualize the fault locations within the topology of your network, as shown in Figure 3. This gives you a 360-degree view of diagnostic analysis, as indicated by the blue arrows in the figure.

Figure 3. WaveSuite provides a 360-degree view of diagnostic analysis for troubleshooting

By combining the 1830 PSS OTDR with WaveSuite applications, you can automatically notify your operations teams of critical events within the network and get key insights and actions that will help them restore the network to its operational state.

The WaveSuite applications support open interfaces and notification advertisements. This means you can easily integrate applications such as WS-AD into more advanced digital process automation and connect them to northbound OSS applications.

With WaveSuite, you can rest assured that as your network begins to scale, you will be able rely on automation capabilities to simplify and streamline your troubleshooting operations so you can reduce network management cost and resolve problems before they cause revenue loss. The results are better risk mitigation, greater efficiency and more value from your optical network.

Learn more

Blog series: Automating optical networks for success

Product web page: WaveSuite

Analysys Mason study: Quantifying the benefits of optical network automation

WaveSuite eBook: Optimize, scale and monetize your optical network

WaveSuite application note: Get ready to automate the delivery of optical services

Data sheet: 1830 OTDR

Fault detection use case: Using AI and automation to protect optical networks from fiber cuts