networks driven by high speed applications mean that
more users are now demanding fibre all the way to the
desk. It's not hard to provide either but because there's
more than one implementation solution, you need to assess
how best to meet your users' needs.
organisations can now justify providing fibre to the
desk in view of the volume of data that users need to
share and process. Emerging applications such as design
companies employing large CAD files, multimedia creation
and videoconferencing are just three examples demanding
high bandwidth. The immunity of optical fibres to electrical
interference is a prime consideration where data handling
takes place side by side with electrically 'noisy' industrial
processes. Finally, where total security of data transmission
is paramount, fibre wins hands-down over other solutions
Differing users mean different solutions
users-from pharmaceutical companies to aerospace firms
and from design consultants to the corridors of power
-now specify fibre to the desk or workstation. But since
these installations vary widely from an environmental
viewpoint, there's no one-size-fits-all solution. The
installer must select a system which is relevant.
There are four options:
Fibre direct to the desk or user.
Fibre to the nearest wall outlet, with conversion
to copper handled there.
Fibre to the node of the user group, then copper to
Hybrid fibre and copper cabling.
Each is handled slightly differently, so let's take
them in turn.
Fibre to the desk
is the only system that truly provides fibre all the
way to the desk; the other three schemes involve a copper
'tail' and are thus composite solutions. The gap between
the outlet and the user's PC or workstation is spanned
by a fibre patch cord containing a flexible glass fibre
protected by a relatively thick plastic sheath.
Generally these patch cords are fitted at either end
with SC, ST or MT-RJ connectors; The MT-RJ are remarkably
similar to the RJ-11 and RJ-45 connectors used for telephone
and data cables. The optical data outlet can be on the
wall (perhaps on a pillar or trunking), in a floor box
or on the desk (if the optical cable is wired all the
way to the desk). The 'near' end of the patch cable
plugs straight onto the optical network interface card
(NIC) in the PC and this card does the signal conversion
from pulses of light to electrical data signals.
on image for larger view
to the nearest outlet
Here again the outlet can be on the wall or in a
floor box. Optical NICs are not required (saving considerable
cost) and a media converter is provided at the outlet
(physically this is no larger than a dual-gang mains
power point socket). Standard NICs are used in users'
PCs, with standard copper patch leads (either Cat 5e
or Cat 6) between these and the media converter. This
solution combines the intrinsic benefit of fibre close
to the desk with the cost benefit of using copper NICs.
It works well for 10/100Mbit/s Ethernet applications
and provides an easy upgrade path for a complete fibre
direct to the desk solution (for example shared Gigabit
Ethernet) at a later stage. It is ideal for industrial
and office installations.
Fibre to the node of the user group
kind of installation is very similar to the foregoing,
except that the fibre is terminated on a shared media
converter or hub at a convenient place among a group
of desks, on the wall or in a floor box with copper
cabling then being fed out in a local star to the surrounding
desks. It has the same applications and advantages as
the last scheme.
Hybrid fibre and copper cabling
system is ideal for organisations with budget constraints
but also having a clear idea of current and future needs-the
ultimate upgrade path. Copper cables and dark fibres
are installed side by side, using the same configuration
layout as for a standard copper installation. When the
time comes to light the fibre and transfer to the optical
medium, new terminations are provided and the copper
infrastructure can be either cut back or retained for
voice telephony applications.
Providing fibre as well as copper cable at the outset
means the infrastructure costs are initially higher
but no further backbone cabling is required, meaning
lifetime cost of ownership is significantly lower. This
is a prudent solution for the typical IT manager and
is very appropriate for the any environment where copper
is a good solution now, but where requirements for higher
data rates can be envisaged later.
Now choose your fibre
selection of fibre to be used depends very much on your
anticipated future use. Higher-bandwidth 50-micron core
multimode fibre is fine for the medium term (and is
being adopted more and more), although laying single
mode as well would make for an ultimately future-proofed
system. This would be a genuine 'once and never again'
solution, ideal if you have the budget to support the
investment in the active equipment.
An alternative would be to opt for blown fibre, in which
plastic tubes are laid to each user location and fibres
blown in as and when required. Optical cabling can be
provided on either a 'home run' or distributed basis.
Home run involves taking separate fibres from each user
to active equipment at the central comms room of the
system, whereas a distributed system provides intermediate
nodes with active equipment on each floor or in each
cluster of users if necessary.
Getting it right
Cost is usually the deciding factor, and will determine
whether fibre is taken all the way to each user or to
a convenient point for shared media conversion. Home
run systems can work out cheaper for networks with not
many users. The trade-offs for each option are often
quite detailed and complex, meaning it makes sense to
use a consultant or seek advice from one of the major
manufacturers such as Krone. The details they will expect
you to have prepared for them include:
Size of budget for active equipment (the major element
of the total cost);
Level of security required;
Degree of electrical interference likely to be encountered;
Extent of future proofing required;
Current and future bandwidth requirements.
In the final analysis it will boil down to an intricate
table of costs and benefits
and thankfully the
choice of these falls usually to someone other than
Guidance On Fibre Implemen-tation For Structured
following are the recommendations based on the most
cost effective solutions for a wide range of standard
LAN applications. Responsible standards' bodies are
recommended to develop specifications to support these
cable entries in order to promote the use of optical
fibre for Building Cabling by providing the most effective
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