Keeping the light on when the cable gets cut

Whether it’s a rogue boat anchor that clips an undersea cable, a construction crew working on a site with undocumented cable runs or simply a manufacturing fault, cables do fail and can break. Some fibre-optic cables used in the telecoms sector are already over 30 years old with no signs of degradation or failure, a testament to their resiliency. However, even fibre is not indestructible. 

Take this case in point. In October 2016, construction for London’s Crossrail railway construction project near West Drayton station in West London accidentally severed both copper and fibre cables when a pile driver accidentally clipped an underground cable run that passed underneath the railway line. The resulting disruption to analogue and digital services lasted several days. It was a classic example of how complex an unplanned repair of fibre can be for a network operator. Services started being restored when new physical infrastructure was put in place, but the final, long-term fix took weeks and involved multiple repair crews.

Repairing a severed fibre cable is no easy or quick process, especially if it is hard to access under a body of water or buried deep in a metropolitan city centre alongside other utilities, where digging up a street or railway line would create chaos. It means that a damaged fibre cannot always be repaired immediately, and that new fibre cannot always be laid as quickly as a customer needs it. So, what’s the solution?

When capacity drops due to a physical disruption to the network, the traffic must be re-routed across a separate path in the network. As a normal practice, operators carefully design their networks to accommodate for failure instances by duplicating equipment and reserving (tying up) network resources.  But, new abilities with programmable coherent optics and intelligent software control are now opening the door to new ways of operating the network, helping operators increase service availability using existing deployed hardware and network resources.

Using software-defined network (SDN) applications and tuneable optics, the actual limits of a fibre connection can be continually tested and recalculated. Optics can then be retuned to increase the operating capacity of the fibre up to its real physical limits, rather than working within fixed theoretical calculations. While an optical wavelength may normally run at 200G over a given distance taking into account full-fill, end-of-life link conditions, the same wavelength could be lifted to, say, 250G to provide bandwidth cover for a damaged fibre, by tapping into the system margin available with the current state of the network.

We call this notion of real-time optical network optimisation ‘liquid spectrum’, and it is designed to gain optical capacity on-demand, improve reach for a specific channel, or increase service availability as-needed. It uses a combination of instrumented, programmable hardware, in the form of variable-bit-rate coherent optics to enable tuneable capacity and a reconfigurable, flexible grid photonic layer that can re-route wavelengths as needed across the network. On top sits an intelligent software layer. This provides a single, integrated view of the network and provides the intelligence and automation to respond to real-time network performance and telemetry data to optimise the efficiency of the network.

This not only buys time to organise a planned, less-disruptive and less-expensive repair, replacement or installation of new fibre, it ensures continuity and quality of service for end customers, as well as enabling new services to be brought to market faster than it takes to lay more cable infrastructure.

Not only can the intelligent software layer make automated bandwidth decisions to maintain service continuity, it can also use telemetry data to ensure everyday efficiency. 

The unique characteristics of a particular fibre link, including system margin data and overall spectrum management, provide opportunities for proactive network performance optimisation that can far more efficiently use data driven insights, rather than the manual monitoring and line testing achieved today.

Intelligent and tuneable fibre-optic solutions such as Liquid Spectrum are an important step towards fully automated communications networks that can self-heal, bypass problem points, and quickly provision and deploy services to customers. It also provides network operators with an immediate and single view of network health, traffic and revenue-generating opportunity from existing infrastructure. 

With more autonomous networks, the next time an operator has a fibre cut occur or a sudden need for more capacity they can improve service availability, accelerate time to market, and eventually, dynamically move bandwidth easily across the network to address mobile capacity requirements – so the end-user is none the wiser.