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  1. Technology
September 5, 1988


By CBR Staff Writer

Among the more arcane technologies being promoted at this year’s Farnborough International Air Show, which opened on Sunday and runs for eight days, closing on Sunday evening, comes from British Telecommunications Plc. It is a technique that enables the indecisive to wire a building or site for fibre optic cabling, and choose only later which routes the cables should follow. Developed at the company’s Martlesham Heath laboratories, the technique is called blown fibre, and involves using a small air compressor to shoot the cable down previously laid plastic ducts. At present it is being used primarily in military applications and for wiring sites like airfields primarily because these customers are among the first who demand the additional security offered by fibre compared with copper. What are the benefits? Perhaps most important is that wiring an entire building or site with fibre cable is not a cheap operation, and the technique enables wiring to be carried out progressively over time as requirements expand. A second benefit is that users may want to migrate to a new type of cable multimode to single mode for example, and Telecom reckons that it is much simpler to blow the old fibre out – yes, it works both ways – and blow the new in, than it is to relay the cable ducts. Physical damage Moreover Telecom is at present using four-strand fibre but has applied the technique to seven-strand, another possible reason for users wanting to upgrade in the future. A further benefit is that – just like Compact Disks, optical fibre is rather less immune from physical damage than early proponents of the technology suggested. Laying cables when a building or site is being wired, or drawing them through the ducts, leads to stresses in the cable that can lead to progressive deterioration in damp conditions. The technique works for stretches up to 1,500 feet, after which the compressed air runs out of puff, but that does not mean that the cable has to be broken at that point: it can be looped out of the Microduct and blown on for a further 1,500 feet, and British Telecom has achieved a total distance of just over two miles on a test run, and reckons that 6Km – three and three quarter miles – is definitely on, the distance finally being governed by the lengths in which the cable is supplied. Any old fibre cable? By no means: the cable needs to be sheathed in a special high friction coating so that the compressed air has something to bit upon: it is manufactured by Optical Fibres Ltd of Deeside. The next step will be to perfect techniques for using the concept with British Telecom’s Open Systems Cabling offering for the local area network market. It reports that two or three firms putting up new buildings – banks, an oil company, have specified the Microducts which carry the cable, and that it is also of keen interest in UK government contracts on which the company is working or bidding. At present, the blown fibre is confined largely to laying the backbone of the network, but Telecom is working on techniques to bring it right to the desk, where the frequency with which office layouts get altered will make it particularly attractive. British Telecom has licensed the technology to the giant Japanese Sumitomo group, and looking around the US and Canada for possible partners or licensees – or even acquisitions through which it can push the concept.

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