Bandwidth-hungry 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.

Many 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
Numerous 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 each user.
• Hybrid fibre and copper cabling.

Each is handled slightly differently, so let's take them in turn.

Fibre to the desk
This 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.

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Fibre 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
This 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
This 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
The 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 the installer!

Guidance On Fibre Implemen-tation For Structured Cabling Systems
The 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 technology possible.

Nagendra can be reached at nagendra.ds@krone.com