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FREQUENTLY ASKED QUESTIONS

Question: Blown Fibre vs. Conventional Fibre
Answer:

Blown fibre clearly has its applications, whereas there are some applications where it would be less suitable than conventional fibre.  Long distance intercity routes will, for instance, remain the domain of conventional fibre.

Blown fibre comes into its own in the case of shorter routes with frequent branch-outs – especially where the future need for fibre is unclear.

Areas where blown fibre excels are the following:

  • As a backbone in high-rise buildings
  • Fibre to the desk solutions
  • Campus architectures – academic, business, industrial or residential
  • Metropolitan City Rings
  • Access Networks
  • Fibre to the Home
     
Question: What is blown fibre?
Answer:

Firstly, the fibre in "Blown Fibre" is ordinary, standard optical fibre, available in single mode and multimode, with the same characteristics and meeting the same industry standards as the fibre in conventional fibre.

This means that the fibre in "Blown Fibre" can do all the things that the fibre in conventional fibre can do, and is terminated, spliced, etc., in exactly the same manner.

What is unique to Blown Fibre, however, is the packaging and the method of delivery.

Short description

Blown Fibre is a modular optic fibre system in essence consisting of two parts:

  • a tubing system consisting of bundles of specialised very thin PVC tubes, and
  • a number of fibres bundled together with a very specialised coating.

The first step in the installation process is to install the tube bundles along the route and thereafter the fibre bundles are blown into the tubes by means of compressed air.

Tubes

The basic tube is relatively thin, for instance with an inner diameter of 3,5 mm and an outer diameter of 5 mm and is manufactured from polyethylene.  It has an inner coating that minimises friction.

The basic tubes are bundled together in a protective outer sheath of medium or high-density polyethylene together with an aluminium layer.  The number of basic tubes in a bundle can vary (for instance, bundles of 1, 2, 4, 7, 12, 19 and 24 basic tubes in a bundle).  The bundles come in various lengths up to 4 000 metres.

Tube bundles for specialised applications, such as direct burial, low fire hazard and gas-block are also available.
Question: Fibre blowing?
Answer:

After the tubes have been installed along the route, the fibre bundles are blown in by means of compressed air. 

The supply of compressed air could either be bottled or could come from a compressor.  The air should be relatively dry and should have a compression of around 10 bar.

What is of utmost importance to note is that the fibre is not pulled into the tubes by the compressed air, but is carried along its whole length by the airflow caused by the compressed air escaping through the end of the tube.  The fibre bundle actually floats along the tube on a cushion of air, thereby eliminating all possibilities of the fibre being stressed during installation.

The normal speed of progress of the fibre along the tube is around 30 metres per minute, which means that a thousand metres can be blown in approximately 30 minutes.
Question: What is Cost of Ownership?
Answer:

As far as the client is concerned, what really counts over a period of time is the Total Cost of Ownership.  From this perspective blown fibre is in a very strong position.  And the longer the period of the perspective, the better blown fibre looks.

A variety of factors contribute to Total Cost of Ownership.  Some of these are clearly visible and easy to budget for, whereas others are subtler: -

  • Initial cost of material – fibre cables, trunking and sub ducts versus blown fibre tubing and fibre bundles. (This is easy to calculate.)
  • Installation cost – building of routes, pulling in of fibre cable, versus installing blown fibre tubing and blowing in fibre.  (This is still easy to calculate – but please make sure that you take everything into consideration.)
  • Damage to the fibre during installation, especially when construction is still going on at the site; also possible damage to fibre cable by excessive pulling.  (Even this is not so difficult to make provision for, yet.)
  • Damage to the route after installation when someone digs a new trench and cuts off the fibre – it is much cheaper to repair a blown fibre route than a conventional route.  And the result is better.  (This becomes more difficult to calculate up ahead.  And of course you hope it will never happen.  But doesn't it?)
  • Future proofing is cheaper, much more predictable and reliable with blown fibre than with ordinary fibre.  (Try calculating this one!)
  • Downtime in case of extensions, modifications or repairs to the route is kept to a minimum and is sometimes not necessary at all.  (How do you calculate the cost of down time?  You only know that in most cases the cost is more than the client bargained for.)
  • If the business succeeds and prospers, the client is going to either extend the network at some time or upgrade the fibre.  (The value of this is not calculable.  But now the owner of a blown fibre network is in the pound seats.  It costs him/her very little to extend the network.  If the client wants to upgrade from multi-mode fibre to single mode all that has to be done is to blow the existing fibre out and blow new fibre in – at a fraction of the cost of building a new route.  The same goes when, after a time, the fibre degenerates and has to be replaced.  Rapid deployment again limits down time to a minimum – if it is not totally avoided.)

To sum up:  There may still be an argument about the initial cost of a Blown Fibre installation as compared to conventional fibre.  But if one takes a longer time perspective this changes dramatically.  There is no question that over a period of two years the Total Cost of Ownership is lower with Blown Fibre.  And beyond two years …!