Embarrasingly enough I heard this term not so long ago and didn’t have a clue as to what the person was talking about.The good news is that it’s nothing new – a well laid out network will utilise extra network cabling or lines which although unused saves the considerable expense of having a civil engineering company from having to re-lay cabling when the need arises . Of course in the event of a failure of one or more lines there is now also a redundancy check in place. These unlit or ‘dark strands’ of unused fibre can be leased out to companies requiring optical connections. Interestingly, the term ‘dark’ is still used if lit by the lessee and not by the owner.
With the advent of wavelength-division multiplexing, similar to frequency-division multiplexing (no, not a new term, we studied this in the 70’s already with regards to marine telecommunications) many more lines of unused fibre optic cable became open due to the numerous data channels now being supported on one line especially when using Dense or Coarse Wavelength-Divison Multiplexing. Wiki states that the costing currently for hosting fibre optic reduces by half every nine months. (Moore’s Law).
For those living on the African continent there are many articles written about Dark Fibre Africa (DFA) which may pique interest.
SEACOM: The inherent risks associated with the laying of cable are huge and mistakes can cost upwards of hundreds of millions of dollars. Seacom was tasked with providing and laying cable to the African continent – a very good read and insight into Seacom can be obtained here.
Laying submarine cable: