Friday, 8 June 2012

Blown fiber vs. "real" fiber

Courtesy of
Blown fiber was an excellent innovation - by using cheap plastic ducts (pipes), telcos could employ cheap labour to run ducts from the exchange to their valuable business customers and a second team could come along later and using their specialist equipment simply push a strand of fiber optic cable from the exchange to the customer.  The first job, including planning, obtaining wayleaves, digging up the road and making good, breaking access routes into premises and finding routes within buildings to run the duct to the cutstomer's equipment was time consuming but fairly straightforward civil engineering taking weeks.  The blowing of the fiber is the work of an afternoon, and so a two man team can do two jobs a day.

Running fiber between exchanges was a different matter - the number of premises is low (less than six thousand nationwide,) the routes between them already identified with existing cable runs, and the reqirement for fiber counts is high - it made sense to run bundles of hundreds of strands of fiber on these routes.

So there came to pass two ways of running fiber.  One suited to low-density installations - where few high-value customers in random locations need a dedicated link and the other suited to fiber-rich high-bandwidth readily identified premises.

Armoured Fibre Cable for Direct Burial

How does this affect rural broadband projects?  If you ask a fiber supplier which technology should be deployed for a fiber access network (FTTH) they are likely to recommend blown fiber as this has been the standard for many years.  But rural fiber networks aren't like traditional deployments.  The ambition is ubiquitous coverage - fibre to everyone - not sparse networks serving only a few of the premises in an exchange area.

Deploying blown fiber also has a cost - it could turn out to be dearer than direct burial or OHP.  The fiber inside costs basically the same so the cost difference is the expensive ducting system (and apparatus to operate it.)  Blown-fiber technology suits the deployment model for the national telco with random site connections coming in according to customer orders, with third-party contractors doing the digging.  A rural broadband project is engineered differenctly - the target area is to be flood-filled with access network in the same dig, with all the planning and engineering problems solved in one go.

The second drawback with blown fiber is maintenance - traditionally installed broken fibers are easily fixed by digging and splicing new.  Duct systems are more time consuming and costly to repair (even the unused ducts have to be made good) and the manufacturers recommend that broken fibers are blown out and completely replaced in the event of a break, increasing the cost and time-to-fix.

So if you are contemplating a rural fiber install, please consider the simpler approach of installing regular fiber cable day one rather than a blown fiber system, you might save money and it will be a lot easier to repair when the rogue JCB strikes.

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