Remote Fibre Monitoring

Optical cabling supports the communication infrastructure of our connected planet. Inherently fragile by nature, this same optical cable is susceptible to water ingress, misplaced construction digs, rodent infestations, security intrusions, and many other potential hazards. Maintaining optimal fiber condition and performance requires advanced fiber monitoring practices to identify and react to problems quickly.

New technology and network expansion continue to push the boundaries of fiber optic monitoring capabilities. Submarine cables are extremely long fiber optic runs laid in trenches on the ocean floor, installed by specialized ships at a rate of 200 kilometers or more per day. While the value of these optical fiber runs is obvious, the expense of installing and maintaining them can be considerable. When problems occur, divers or robotic vessels may be required to investigate and repair defects. Robust fiber monitoring can lead to earlier detection and precise locating capability, thereby reducing reaction and repair times.

Fiber optics continue to usurp the territory once dominated by conventional coaxial cabling and telephone wires. Fiber to the home (FTTH) is now becoming more common, with direct fiber optic runs to individual homes enabling higher bandwidth and improved data integrity for users. Extending the reach of fiber optics is inevitable, so fiber optic monitoring systems must now be capable of accurately detecting fiber faults from the source all the way to the subscriber.

Fiber optic security concerns have become increasingly relevant as more intrusions and data theft incidents are reported each year. Although fiber optic cabling is generally perceived as being more secure than conventional cabling, fiber tapping incidents continue to challenges authorities and fiber monitoring system capabilities.

Tapping techniques, including the introduction of optical splitters or fiber bending to induce leaks, have continued to evolve in an attempt to elude detection. Encrypting data is an obvious first line of defense for such intrusions, but fiber monitoring technology can also be used to identify the shifts in optical feedback that the perpetrators seek to disguise.

One innovative approach to fiber monitoring that can improve security with minimal additional hardware infrastructure is active fiber monitoring (AFM). By detecting small changes in light transmission across active fiber lines, alarms can be raised so that appropriate security measures can be taken. Using AFM, it is not necessary to dedicate additional fibers for monitoring purposes, since active fibers already carrying high priority data can be strategically selected for observation.

A remote fiber monitoring system enables the oversight of an entire fiber optic network, including dark fiber, from a central location. Using this comprehensive method, the performance of the network can be continuously evaluated, and Mean Time to Repair (MTTR) can be minimized.

MTTR is the measure which best encompasses the overall effectiveness of a fiber monitoring and management system. This is simply the average amount of time required to troubleshoot a failure and return the system to working order. The repair and troubleshooting process is made up of the “find" or fault localization process and the repair process. When a major break or bend event occurs, often 4-5 technicians are dispatched over 4-5 hours to find the problem before the fix can be made. Remote monitoring reduces the localization portion of the repair process to less than five minutes and is done remotely and automatically. This is typically 30-40% of the full span of the repair process timeframe. Thus the accuracy of remote fiber monitoring, utilizing OTDR technology to pinpoint fiber faults, is one key to minimizing MTTR and improving user satisfaction.

Alert messages produced by remote fiber optic monitoring systems can be communicated via email, as well as SMS or SNMP protocols. SMS messages are simply out-of-band text messages that are automatically pushed out to the appropriate users when alarms occur. This can minimize the need for constant oversight of monitoring interfaces. Simple Network Management Protocol (SNMP) is another communication tool that is commonly used to monitor devices remotely and relay alerts to a central location or host.

Despite the effectiveness of OTDR technology, the existence of dead zones in fiber optic links are a potential source of fiber monitoring uncertainty. A dead zone in an OTDR measurement can occur when there is a high reflectance event in the fiber line. This can be caused by air gaps, splices or connectors that produce a sufficient level of reflectance to temporarily saturate the OTDR detector.

During this “black-out” period while the detector is recovering from the saturation, the OTDR will not be capable of accurately discerning other nearby events in the fiber line. This becomes important when a fault condition arises close enough to an existing splice or connection such that a new issue is obscured by a pre-existing reflectance source.

Another common component of fiber optic networks that can lead to challenges as well as opportunities is the prevalence of dark fiber. Despite the ominous-sounding moniker, this term simply refers to the presence of unused or “unlit” fiber in the network. This descriptor is also sometimes used to describe fiber optic cables that are leased from the original carrier to another party.

This dark fiber still requires testing and monitoring to ensure integrity, particularly if the fiber is designated for future expansion opportunities. The presence of unused, terminated fibers can sometimes prove advantageous for monitoring. Fault conditions will usually affect all fibers in a cable, so monitoring of selected dark fibers is an effective way to continually verify the cable integrity without disrupting the active fibers.