FEATURE INCREASING AVAILABILITY OF SUBSEA TELECOM INFRASTRUCTURE THROUGH MONITORING VIBRATIONS IN OPTICAL FIBRE SUBSEA CABLES BY STEINAR BJØRNSTAD, ANDERS TYSDAL, AND CATO LAMMENES
ABSTRACT
Society’s reliance on telecommunication infrastructure continues to grow as both energy and telecommunications solutions share mutual dependencies. This dependency calls for increased monitoring of fibre networks and fibre optic subsea cables, which serve as the backbone of connectivity for all digital communications. Distributed Acoustic Sensing (DAS) and State of Polarisation (SoP) monitoring provide real-time measurements of vibrations and potential mechanical interference which could impact the cable. Implementation of these sensing technologies mitigate risk to the infrastructure, preventing equipment failure and downtime. In particular, any unexpected movements caused by subsea activities such as passing trawlers, hooking of equipment on the seabed, and any geophysical phenomena can be traced so that appropriate action could be taken. This article will explain the capability and benefits of the monitoring system and how Tampnet utilises this system for monitoring its vast subsea and terrestrial cable systems.
INTRODUCTION
Society is increasingly dependent on digitalization and the underlying communications network infrastructure. The fibre network is becoming increasingly important as it is being rolled out closer to the end-user and is now widely deployed in access networks. For the intercontinental network traffic, subsea fibre cables have been the main carrier for a long time, and are now carrying more than 99% of all traffic. A vital component of traditional offshore energy production infrastructure, subsea fibre cables are also
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present in the offshore renewables space, with wind farms utilising combined power and fibre cables. In this design however, the “export cable” running from the wind farm to shore is a single point of failure. A break in this cable would require shutdown of the wind farm over several weeks until a cable ship was available to attend site and carry out repairs, resulting in a significant economic loss. In recent years, cybersecurity has focussed on attacks at the IP-layer and above with little attention paid to physical layer communications. While a Denial of Service (DoS) attack may cause hours of downtime, a physical layer failure may result in an outage spanning days or weeks or leave users with poor service availability. A prime example of this is the recent outage at the Faroe Islands in October 2022. After a failure on one subsea cable, the second failover cable was cut by a fishing trawler, subsequently cutting the island off from the world for several days until repairs could be carried out. Hence, redundancy at the physical layer through availability of several diverse physical paths is imperative. In the Tampnet North Sea fibre network, multiple subsea fibre cables enable redundancy through a mesh network with physically diverse paths. Whilst redundancy is vital, avoiding cable failures is preferable to mitigate high repair costs, outage time, and potentially reduced service quality. This is especially true for facilities like offshore wind farms where redundant fibre paths may not be available. The remainder of this article explains how the fibre itself can be used as a sensor to detect any mechanical interference and vibration caused by operations in the vicinity of