FEATURE FIBRE OPTIC NETWORKS
Optical Fibre Cabling – the Importance of ‘Getting it Right’ Measure Twice, Cut Once By Mike Gilmore, FIA
Compare the application of balanced and optical fibre cabling within customer premises cabling. Of course, copper cabling has the lion’s share by volume and value, and as a result, longer term decisions have to be taken in terms of choosing the right product to get the desired lifetime from the overall installation. Nevertheless, except in specific areas requiring enhanced levels of data processing, the networks operating over that cabling will rarely tax the performance it provides. Indeed, most installations of
balanced cabling do not achieve their initial objectives, not due to any failure of installation procedures or the performance of the fixed cabling under the floors but because of the mismanagement by users of operational matters such as the procurement and installation of the various cords providing equipment or patch connections. Will such performance shortfalls be noticed? Generally not, since the networks operating over them are relatively undemanding. For example, Category 5:2000/
Category 5e cabling is more than capable of supporting 1000BASE-T. However, many users are still operating 10BASE-T or 100BASE-T and even those actually using 1000BASE-T equipment are under- utilising the network to the extent that transmission errors are almost unnoticed. While the trend toward real-time Ethernet applications such as VoIP and video conferencing applies more pressure in this area, one also has to remember that many users have specified, and spent increasing amounts of money on, Category 6, 6A, 7 and even 7A cabling components with the intention of producing Class E, EA, F and FA performance implementations. These transmission classes have enormous headroom in support of applications up to and including 1000BASE-T, and while 10GBASE-T represents a challenge for Class E, it is no match for the higher class implementations. Against this background, one may ask just how long users with such systems will have to wait before the performance they paid for is actually going to be needed.
10 NETCOMMS europe Volume I, Issue 6 2011 This situation presents a complete
contrast to that surrounding optical fibre cabling. The cost of optical transmission equipment tends to force the use of the optical alternative only where really necessary. This tends to mean that the target networks are implemented at, or close to, the completion of the installation and that demands on the installed cabling will only ever increase. The design performance will be required early in the life of the cabling and any failure to deliver that performance is more likely to be identified quickly. Consequently, it will be no surprise
to learn that the history of installation standards for optical fibre cabling is much longer than for its copper counterpart. In 1988, work started on the development of what became BS 7718: A Code of Practice for the Installation of Fibre Optic Cabling. The work was completed in 1990. By comparison, copper is a late-comer. Installation standards that included balanced cabling were only published in 2000. The related test methods were also published in 2000 but are in continual amendment/revision to keep up with ever increasing test frequencies. The FIA has been directly involved
in the publication of all European and international cabling installation standards that address quality assurance, planning and practices. Indeed, a large part of the contents of the original BS 7718 have been transcribed into the later standards, and widened to cover all media. ‘Getting it right’ for optical fibre
cabling never diminishes in importance; in fact, it is more relevant now than ever before. The continuing evolution of data rates maintains pressure on design performance with, at least for the more common multimode optical implementations, ever shorter distances and more stringent performance requirements being applied. The push towards shorter channel lengths actually increases the market penetration of the optical medium but the associated demands on transmission performance represent challenges for component performance and test methods. For example, support for 10 Gigabit
Ethernet over distances of up to 300 metres is provided by Category
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OM3 cabled multimode optical fibre. However, to do so requires a maximum cabling attenuation of 2.6 dB. Provision of that performance, and the ability to measure it accurately, is therefore vital to avoid disputes. This emphasis on testing is not accidental since although the basic methods of test have not changed since BS 7718, the process controls required to obtain more accurate results have become much more demanding and costly. It is a paradox that copper cabling
installers grudgingly accept the use of test cords costing hundreds of pounds to prove to a customer that they have obtained an installed performance that the customer may never need to rely on, whereas for optical fibre, where the desired performance may well be required from day one, the temptation is to ignore the testing standards and apply a cheaper solution. This problem is growing as new “installer” entrants are attracted into the market. There have been cases where users have purchased fault-finding services where the installer came armed with no more than a visible light source (more commonly termed a ‘torch’). ‘Getting it right’ in relation to the
design, planning and installation of optical fibre cabling has always been at the forefront of the FIA creed. Most FIA members recognise the value of this work and take on board the lessons provided by the resulting documents. However, educating the users as to what should be the minimum requirements of a professional service is equally important. The FIA Barebones Requirements documents are accessible to all users and cover topics such a termination, testing and inspection of cabling. They are not intended to replace professional standards, but exist to prevent basic errors on behalf of users. ‘Getting it right’ requires a two-pronged approach: establishing the highest standards of quality assurance, planning and practices, while ensuring that users know when they are being misled. The FIA is implementing both approaches in an effort to ensure that installations are able to provide their design objective with least risk to all involved.
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