Insight: Telecommunications on the ring of fire

New Zealand is a seismically active country so close attention has always been given to mitigating the potential impacts on telecommunications.

Examples of mitigating activities include:
• Core transport networks are designed with geographic diversity.
• Stringent engineering formulas have been used for network deployment.
• Telecommunication buildings have a high intrinsic tolerance of earthquakes.
• Installations all have standby power (whether batteries and/or generators).

On 14 November 2016, the South Island was hit by a massive quake some 95km from
Christchurch affecting the whole of the eastern side of the upper South Island and
isolating the Kaikoura andWaiau townships. The major impact on telecommunications was the loss of the Eastern core fibre route, co-owned by Chorus, Spark and vodafone. It
was severed in multiple locations due to massive landslides over the coast road and
tensile stresses where the surface ruptured. The district became a telecommunications
“dead zone” with telcos blind to the impacts as surveillance and network management
links were lost.The Kaikoura local exchange remained operational using power from
batteries and a built-in generator. Further out and especially in the more remote rural
areas, customers either lost service immediately or progressively as the batteries
of the remote installations ran out. Airborne reconnaissance revealed the full extent of
damage; reconnecting Kaikoura to the rest of New Zealand was not going to be easy.

Initially installation of a new, and reconfiguration of an existing, digital microwave radio link re-established limited mobile coverage and a full emergency services paging service with the remaining capacity for telephony. Further radio augmentation was considered but the favoured remedial solution was to exploit the only intact fibre link in the area which was the vodafone “Aqualink” cable, a near-coast marine cable between Christchurch and Wellington.The cable comes ashore 20km south of Kaikoura and, just north of Kaikoura, there is a land-based repeater before it reenters the sea.The terrestrial section of Aqualink suffered damage but continued to work. It would be possible to intercept the cable at the repeater site and,with a minimum fibre lay, connect it to the “normal” Eastern core fibre link. With goodwill – and some horse-trading – normal mobile and fixed line services (including broadband) were restored just four days after the quake.

Damage to the Eastern core fibre covered a distance of over 84km.Although accessible in some areas, in many others it was buried under hundreds of tons of rock. Where the actual fault location was not accessible, restoration was by a installation of cable overlays from tens to 100s of metres. Extensive use of helicopters achieved many of these overlays.To date the traffic into the Kaikoura area has been left on the Aqualink as the works to reliably restore the Eastern core fibre will take over 12 months.

End users’ access in the Kaikoura area is predominantly over copper with some radio to more remote areas. Impacts were greater in the rural areas; tensile forces pulled joints apart or fractured copper pairs. Displacement of bridge abutments and culvert crossing also caused cable failure. Cable testing indicated that some cables had been significantly stretched. Aftershocks were a problem often resulting in another fault to a previously-repaired section. For customers fed by radio, the main problem was power failure once their battery supply was exhausted, typically within 24 hours. Standby generators were deployed but had to be airlifted by helicopter and the refuelling runs added significant cost. Helicopters were used to transport the technicians and special precautions had to be implemented to ensure staff safety.

A number of lessons were learned from this
• The importance of having good civil defence arrangements in place was key to managing the situation.
• Getting to the faults quickly is vital; ingress of water into a cable or leaving batteries in a discharged state for too long exacerbates the fault.
• Events such as this remove any complacency about ensuring fibre optic links and electronic systems have sufficient diversity.The “Aqualink” cable sharing solution shows that there is potential to look further into creating physical network sharing contingency
• The New Zealand Government is undertaking a review of the level of resilience across the entire telecommunications sector and the extent to which telcos were able to able to fulfil their legal civil defence emergency obligations.

This is a summary of a full article which appeared in The Journal, Volume 11, Part 2. Read the full article here (free for members).


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