Viewpoint
Building, activating, and maintaining submarine cable networks presents unique challenges associated with accessibility, long distances, and constant exposure to the elements. Throughout the life cycle of a submarine cable network, it is critical to use the right test and monitoring tools.
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Construction
During construction, end face inspection can detect dirt particles or other physical defects whose impact can either diminish or halt network performance (and produce bad test results). Perhaps the most essential tool for physical layer fiber verification is the OTDR (Optical Time-Domain Reflectometer). Specialized types can be used for long haul wet plant OTDR as well as versatile bidirectional dry plant OTDR. Another parameter which must be measured and controlled during cable deployment for submarine network construction is the amount of strain being placed on the actual fibers, this must be lower than 0.34% for submarine fiber grade (IEC 60794-3-20), higher values will reduce the life span of the fibers. Strain measurement can be performed using portable Brillouin OTDR. Optical dispersion tools are also pivotal to the characterization of submarine cable networks in order to base line optical dispersion and assess if any dispersion compensation is required.
Activation
Service activation requires tools for optical power measurement and spectrum analysis along with data network equipment testing. In order to quantify optical power, a ruggedized optical power meter is an essential tool. High quality Optical Spectrum Analyzers (OSA) for performing Optical Signal-to-Noise Ratio (OSNR) measurement and Network testers for latency, throughput, jitter, and frame loss/bit error rate analysis are also a must during this phase to validate and certify network performance.
Monitoring & Maintenance
Monitoring and maintenance are the keys to keeping the vital submarine cable networks performing optimally. To assess the fibers physical health, an effective optical network monitoring system can provide real time fault, degradation, and security issue monitoring.
Fiber monitoring of links is an essential ongoing function. It can be used to detect fiber degradation and a wide array of fiber monitoring techniques may be utilized to meet the unique challenges associated with a submarine cable fault. For example, to detect fluctuations in strain, temperature and other parameters inherent to submarine cables, fiber optic sensing tools play a critical role. In addition, service performance monitoring is key to pro-actively identifying data issues (such as latency, throughput, jitter, and frame loss/bit error rate) and is usually required in order to prove SLA compliance for customers.
What to Measure and Certify
The complexity of a submarine cable network makes it extremely important to test and certify all segments of the wet plant, dry plant, and landing station including the interfaces between these elements. For the wet plant, OTDR testing is vital to measure attenuation across the entire length of the submarine cable.
For repeated systems, this includes measurement through the in-line amplifiers. For non-repeated systems, long range OTDR may be required. Other testing required to certify the wet plant includes chromatic dispersion (CD) and polarization mode dispersion (PMD).
The dry plant must also be tested and certified, including a verification of error free data transmission to the wet plant. The integrity of SLTE patching and the manhole splice should be verified. Optical Spectrum Analysis (OSA) through the dry plant connection is another critical test point. The data networking elements of the landing station must also be vetted, along with the fiber backhaul. As with a purely land-based network, latency, throughput, jitter, and frame loss are potential test metrics to assess performance. The time associated with protection switch service disruptions should also be evaluated.
