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.