Case Study – Access Networks
Despite popular opinion in some quarters that blown fibre solutions were
first introduced forin-building networks, because they are too fragile for the rigours of
application in externalenvironments, blown fibre was originally developed as a solution for Access
Networks and hasbeen most extensively used for last mile customer connections around the world.
None more so than the UK, where, for approaching 15 years, blownfibre units have been
installed into cables containing a number ofempty tubes, primarily 4 tube Direct Install assembly,
to build theaccess network for business customers in towns and cities. In fact,for any industrial
or commercial customer whose requirements justifythe provision of an optical fibre connection,
blown fibre has beenused. While the standard approach has been to install one or a number of 2 or 4
singlemode fibres into the available tubes, theflexibility of the blown fibre solution means that
in recent yearshigher fibre count units (8 or 12 fibre) can address larger customerrequirements or
provide a growth path to add capacity at a laterstage. As the bundles can be blown out and
re-utilised if required,more capacity can be offered by replacing a 2 fibre unit with a 4, 8or 12
fibre unit should there be no available tubes to blow in extrafibre units.
Flexibility is being further enhanced by adopting newer fibre
types.In-building or campus networks may evolve from multimode 50/125and 62.5/125 to OM3 or
singlemode to accommodate faster speedsor longer distances and networks may incorporate different
fibretypes depending upon the application and configuration. In accessnetworks, where singlemode
fibre is the standard and the use of NZD(Non-Zero Dispersion Shifted) fibre is unlikely to be
applicable (beinggenerally used for high bit rate, long haul networks) the only likelytrend could
be toward low water-peak fibres
These fibres extend the bandwidth and so the capacity of singlemodefibres by making
available for transmission the region around1383nm, traditionally effected by the naturally
occurring water peakin fibres causing higher attenuation. Some customers have adoptedthese fibres
(Prysmian’s MagniLight fibre) in their blown fibre networkas part of their future-proofing
strategy, despite the fact thattransmission equipment is not yet available to utilise
thesewavelengths. In fact most operators prefer to deploy standardsinglemode fibre on day one, and
they intend to upgrade toMagniLight fibre if and when they require the extra operating
window.
In a typical access network, the distance of the final drop to a
businesscustomer will bea few hundred metres. All of the Sirocco blown fibrebundles (2 to 12 fibre
irrespective of fibre type) will blow around1km in a single point-to-point route in these
applications, makingplanning simple, as long as the recommended Sirocco tube is used(these lengths
may not be achievable using other manufacturers’tubes as the tube inner liner has a major effect on
blowing distances).With the tube cable in place, installation of the blown fibre unit in anaccess
network will be achieved in less than 15 minutes for a typicalroute, ready for splicing and
termination.
Sirocco Features and Benefits
· Avoid dark fibre investment
· Flexibility to add capacity at a later date
· Introduce new fibre types when required
· Achieve 1km blow length, sufficient for access connections
· Capacity upgrade – blow in 15 minutes
· Blow to building entry or straight to internal presentation point
In the UK, the standard approach is to deliver the blown fibre into the
building and terminate it at the building-entry point (the internal network being the
responsibility of the building owner or user). Elsewhere, the blown fibre may be blown from the
external network node right to a presentation point anywhere within a building (on the ground floor
or at the 30th floor of a high rise office block). The connection of tubes is a very easy
procedure, simply plugging together lengths of external and/or internal tubing with a plastic
connector (that withstands the blowing pressure during test and installation). The blown fibre unit
can then be blown through a series of lengths of inter-connected tube to the presentation point. If
a diverse feed is required to provide resilience/security, then simply by connecting up alternative
route paths through the network, this can be achieved. A significant cost benefit can be gained
when deploying fibre to many different floors of a high rise office block when using blown fibre
versus conventional cable. The graph below shows the cost benefit derived by one operator when
connecting seven customers within a high rise office block when using blown fibre versus
conventional cable. The cost advantage here is mainly derived from the elimination of costly
installation work carried out within risers and reinstating fire barriers when repeatedly
installing conventional optical cables.
|
