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Fibre all the way
Bandwidth-hungry networks driven by high speed applications mean that more users are now demanding fibre all the way to the desk. Its not hard to provide either but because theres more than one implementation solution, you need to assess how best to meet your users needs. Fibre specialists Steve Webster and David Murray of Krone explain the options. 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
Its no surprise then that numerous usersfrom pharmaceutical companies to aerospace firms and from design consultancies to the corridors of power now specify fibre to the desk or workstation. But because these installations vary widely from an environmental viewpoint, theres no one-size-fits-all solution and the installer must select a system relevant to the physical location under consideration. There are in fact four options we can currently use: 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; and Hybrid fibre and copper cabling. Each is handled slightly differently, so lets take them in turn.
Fibre to the desk
In point of fact, 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 users 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, so to a casual glance the patch cord looks similar although smaller than any other data cable. 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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To sum up, this is a top-end solution, employed where cost is not the key consideration. It provides high security along with high data rates (Gigabit and beyond) and can be used to effectively future-proof a network
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 network interface cards 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 needsthe 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 singlemode 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
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Out on the floor its vital not to skimp on the distribution of fibres, which can be done in similar fashion to the flood wiring used for copper cabling. 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. The latter allows flexibility for subsequent reconfiguration in the future. 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. Physical distance, the number of users and the grade of fibre used will influence the choice here, also future upgrade plans.
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 but this will also depend on the building layout, distances involved and the degree of route diversity you wish to provide in case of damage to cables. 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!
Further information
Fibreoptic Industry Association. Premier UK industry association for fibre networking. Telephone 01763-273039, http://www.fibreoptic.org.uk/. BICSI. BICSI, a not-for-profit telecommunications association, is a worldwide resource for technical publications, training, conferences, and registration programs for low-voltage cabling distribution design and installation. BICSI has over 20,000 members residing in 85 nations. Members can buy the associations installation practice manual, which is the industry bible. Telephone 01206-579899, http://www.bicsi.org/ Telecommunications Industry Association. The (American) TIA describes itself as the leading trade association in the communications and information technology industry. Its numerous standards documents are available for sale on line at its website, http://www.tiaonline.org/
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Fibre patch cable using latching MTRJ connectors. Similar to any normal data cable, although the cable and connector are in fact optical.
In a home run system fibre cables run like spokes of a wheel, from a central point the comms room direct to each user location.
Distributed systems use backbone cabling to flexibility points, then separate cables to individual users from there on.
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