【正文】 ptical Technology Optical technology, on the other hand, is already advanced. It has been improved by the development of extended bandwidth multimode fibre and by the development of the VCSEL laser. The refractive index profile of ordinary multimode fibre does not follow the ideal parabolic variation across the diameter of the core. These fibres have a small index discontinuity located at the axis of the fibre that prevents paraxial rays from being transmitted efficiently. These are the rays that suffer least dispersion and it is low dispersion that permits higher signalling rates to be used. Extended bandwidth multimode fibres have been developed with an improved refractive index profile. They have increased the distance over which gigabit ether may be transmitted by multimode fibres to about 1km. The VCSEL laser is capable of launching paraxial rays along the centre of an optical fibre and is the ideal plement to the use with extended bandwidth fibre. Traditionally, copper works have been cheaper than their optical counterparts, but as data rates increase, the costs of installing these media will converge. This is likely to happen at rates of about Gbs. The Future Obviously, all predictions about future requirements are fraught with difficulty and we must rely heavily on past experience. Errors of judgement when dealing with the horizontal working are expensive and have long lasting consequences. There is usually only one chance to get it right as the lifetime for horizontal wiring is 10 years or more. By way of contrast, the lifetime of a . is about 2 3 years and that of an ether switch 3 5 years. In view of this, it is crucial that the right choices are made for horizontal cabling. For 10 Mbs working, copper category 3 cabling is quite adequate. For 100 Mbs working, copper category 5 cabling is required. For 1 Gbs working, copper category 5e cabling is required. For 10 Gbs working, extended working 50/125181。s occupants, so this sort of activity is normally undertaken when there is a major refurbishment of the fabric. Cableways have to be formed in, on or under walls, floors and ceilings. The installers have to ensure that results are not unsightly but inevitably there is damage to the amenity value of the rooms through which cables have to pass. Care has to be taken to provide adequate and presentable cable containment for both power and voice/data cables. This all means expense. The cost of ownership is high. It was precisely because of these high costs that unshielded twisted pair (UTP) ether was developed. This permitted the use of existing, low grade, category 3 telephone cabling within buildings. Strenuous efforts have been made to improve the bandwidth capabilities of this popular medium. However, once firmly established, economic improvements to this system could be made only by redesign of the cable, leading to the production of category 5, 5e and 6 cables with category 7 in the pipeline. These improvements have enabled the development of 10megabit, 100megabit and 1gigabit ether over UTP. Indeed, it has been said that you can transmit and receive data at gigabit per second rates with acceptable error rates over barbed wire. It39。m fibre. Greater distances imply the use of monomode fibre. Any changes to the building vertical LAN can usually be made in parallel with the existing work services so disruption of the service to the desktop can be kept to a minimum. Because of this, costs to the organisation due to interruption of work service can be kept small. Horizontal LAN When considering the horizontal distribution within a building, we see the same increase in data rates as predicted by Moore39。T solution. A minimum of two ThickWire Ether segments (Belden 9880 or equivalent) will be run through each building to the interconnecting basements. Loops should be left on each floor for future instal cable must have readily available access (. not run in conduit) to insure future use. A minimum of one d in each building riser for future data munications use. Sufficient bulk voice munications riser cable