As System Capacity Appears To Keep On Growing and Growing, Is It Time We Asked: ‘How Big is Too Big'

By John Tibbles
May 28, 2021

Subsea cables have seen an explosive increase in their capacity capability and build the biggest system a sensible objective. But is that sustainable or have we reached a point where that question needs to be asked.

Early Fibre Optics

When ‘Standard A’ earth stations stalked the earth, submarine cables were few and far between. The 30m wide giant white dishes represented a true wonder of the space triggering the explosion of international voice calls drove demand in the 1970s. When the first fibre optic cable TAT8 entered service in 1989, its follow on-TAT 9 was already on the drawing board. In a few short years fibre optic systems had multiplied in the Atlantic and Pacific and a number of ‘private ‘cables had joined the traditional carrier consortium models competing on price capacity and accessibility.

Development is in optical technology and long manufacturing lead times meant each one was more or less obsolescent as soon as it went in the water. System capacity was increasing in a Moore’s law trajectory and as a result the industry adopted an approach of ‘just build the biggest‘ with each new project. And that mostly been the same since. Mostly but not always.

The problem that arose was that each new system in the Atlantic TAT 9, TAT 10, PTAT, small as they seem today, had several times the capacity of their immediate predecessors. The availability of satellite capacity for restoration was disappearing along with the satellite network. The question planners had to face was what do we do if one of the newer ‘super ‘cables breaks. We have nothing capable of restoring it and while performance is good reliability in the event of a cable break is disastrous.

Too Big to Fail

To ensure a reliable resilient ‘system’ the plan was to build a parallel cable and thus loop systems were born. Gemini, AC1 /2 TAT12/13 and Southern Cross. In order to provide the reliability, the market demanded these very large systems at the time needed a second whole cable purely for redundancy. Being the biggest system had its serious and expensive challenges; paraphrasing an industry news item of the time tells the story well.

‘High capacity undersea cable goes live’–The Gemini Submarine cable system has gone live doubling the transatlantic telecoms capacity between London and New York. The first leg entered service earlier this year with the full system scheduled for completion by the end of the year to provide a fully redundant self-healing network. Gemini is being built at a cost of over $500m by a Cable & Wireless and WorldCom joint venture. When completed the system will have a total capacity of 60Gbit/s i.e., 30Gbit/s working with a further 30Gbit/s protection. This will more than double the existing transatlantic capacity – currently estimated by C&W to be around 26Gbit/s

Yes, you did read that right- a whole cable -, the largest capacity system at the time carried 30Gbs. I was forking for Cable and Wireless at that time and at a Management Board presentation our forward thinking and respected Finance Director asked, ‘Will anyone ever use up that much capacity?’

It sounds bizarre today, but in a business still dominated by telephone calls it was perfectly reasonable. Gemini, just one leg, could carry 450,000 simultaneous telephone calls. (The new transatlantic system, Marea, has a capacity of 200Tb/s. That is over 6000 Gemini cable systems!

I will leave to your imagination how many old-fashioned phone calls that represents.

To continue reading the rest of this article, please read it in Issue 118 of the SubTel Forum Magazine on page 50 or on our archive site here.