Case Study – Access Networks
Despite popular opinion, in some quarters, that blown fibre solutions were
first introduced for in building networks, because they are too fragile for the rigours of
application in external environments, blown fibre was originally developed as a solution for Access
Networks and has been most extensively used for last mile customer connections around the world.
None more so than the UK, where, for approaching 15 years, blown fibre units have been
installed into cables containing a number of empty tubes, primarily 4 tube Direct Install assembly,
to build the access network for business customers in towns and cities. In fact, for any industrial
or commercial customer whose requirements justify the provision of an optical fibre connection,
blown fibre has been used. While the standard approach has been to install one or a number of 2 or
4 singlemode fibres into the available tubes, the flexibility of the blown fibre solution means
that in recent years higher fibre count units (8 or 12 fibre) can address larger customer
requirements or provide a growth path to add capacity at a later stage. 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,
8 or 12 fibre unit should there be no available tubes to blow in extra fibre units.
Flexibility is being further enhanced by adopting newer fibre types. In
building or campus networks may evolve from multimode 50/125 and 62.5/125 to OM3 or singlemode to
accommodate faster speeds or longer distances and networks may incorporate different fibre types
depending upon the application and configuration. In access networks, where singlemode fibre is the
standard and the use of NZD (Non-Zero Dispersion Shifted) fibre is unlikely to be applicable (being
generally used for high bit rate, long haul networks) the only likely trend could be toward low
water-peak fibres.
These fibres extend the bandwidth and so the capacity of singlemode fibres by making
available for transmission the region around 1383nm, traditionally effected by the naturally
occurring water peak in fibres causing higher attenuation. Some customers have adopted these fibres
(Prysmian’s MagniLight™ fibre) in their blown fibre networkas as part of their future-proofing
strategy, despite the fact that transmission equipment is not yet available to utilise these
wavelengths. In fact, most operators prefer to deploy standard singlemode fibre on day one, and
they intend to upgrade to MagniLight™ fibre if and when they require the extra operating
window.
In a typical access network, the distance of the final drop to a business
customer will be a few hundred metres. All of the Sirocco® blown fibre bundles (2 to 12 fibre
irrespective of fibre type) will blow around 1km in a single point-to-point route in these
applications, making planning 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
an access network will be achieved in less than 15 minutes for a typical route, 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 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.
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