With growing importance being attached to the provision of complex networking services for companies, there is increasing awareness that the cabling system that connects them should be up to its task. Not only does it have to cater for user needs now, but, given the disruption caused by recabling a building, it is also sensible to cater for future needs, even though these may not even be perceptible at this stage of planning. As with so many other areas of communications, manufacturers have previously concentrated on their own proprietary cabling systems with little apparent thought to the future. But the industry’s preoccupation with the need for open systems is now filtering through to cabling architectures. The adherence to proprietary systems has been largely attributable to the differences that have existed between the various local area networks that are available from manufacturers. Although two basic technologies have emerged in the local network field – Token Ring and Ethernet – there are still differences in the protocols used. Two different International Standards Organisation protocols can be implemented over Ethernet systems: the XNS protocol originally developed by Xerox, and TCP/IP developed by the US Department of Defense.
New entrants According to John Lane, the manager of Butler Cox’s Building Technology Group, which offers consultancy services on all aspects of construction, it is only over the last 12 months that awareness of the importance of cabling for the future has risen significantly. Companies such as IBM and AT&T had already shown their appreciation of the position by announcing cabling systems in a variety of media that cater for the increasingly varied demands being placed on local networks and the number of applications served by them. Over the last year, these new entrants have tended to displace proprietary cabling systems such as the well established IBM 3270 coaxial system as well as broadband and Ethernet backbones running on the traditional coaxial cable. Fibre optic and twisted pair (telephone wire) are now becoming a lot more popular and the bigger players are designing arcitectures which embrace all these media offerings. The most recent entrant to the field has been British Telecom with its Osca Open Systems Cabling Architecture, which joins AT&T’s Premises Distribution System and Northern Telecom’s Integrated Building Distributed Network cabling schemes. Currently the most common configuration is to run fibre optic cable from the main computer to each floor served by the network and then to run twisted pair copper wiring from the riser cupboard to each desk or terminal.
The most expensive part of the operation is the horizontal element. Running cable around an office floor is bound to cause a great deal of disruption. At the very least, desks have to be moved and carpets taken up, preventing people from working, perhaps for weeks on end. Installation of the vertical element is speedier and feasible over the week-end break. Lane considers that installation of a totally fibre network is over-kill for the majority of today’s applications – 9.6Kbps is the speed most commonly used in data transmission. Technologies such as Ethernet have the capacity to transmit data at 4Mbps over copper wires and fibre can provide 10,000 times the capacity of current requirements, far and away above most users’ needs, he says. The other argument weighted against a fully fibre installation is cost. Although the costs associated with fibre are dropping all the time, it still demands a high level of investment. Lane estimates the cost of equipping each outlet, such as a terminal, with AT&T copper cable to be UKP80 and the cost for IBM’s system is higher, at around UKP200 per outlet. But way above, the cost for a fibre installation is around UKP200 for the cable plus UKP300 for the connection at each end, making a total of some UKP800 per outlet. As user requirements rise over the next few years, with the advent of increasingly complex graphics systems and image processing techniques, and fibre costs f
all, the cost of fibre will come more into perspective, Lane believes.
At the moment, even the thought that a fibre optic cabling system will have an extended lifespan in comparison with twisted pair because of its infinitely greater capacity is not enough to persuade the cautious financial controllers of most companies. The argument of amortising the investment over 10 or 15 years rather than the five envisaged for copper cabling is not sufficiently attractive to sway them. Part of this reticence is perhaps due to uncertainty about how fibre will be installed in five years time. British Telecom has developed an approach known as blown fibre, for future use (CI No 1,008). Where fibre cable is not yet required but is likely to be needed in the future, Telecom is installing plastic ducting through which fibre optic cable can be blown when it is needed. How competitive this technique will prove to be in the light of future developments remains to be seen.
Carpets and desks Industry reckons that 30% automation among a workforce to to be the critical figure to justify re-wiring of a building. Furthermore, if 30% of the terminals employ graphics, fibre optic cabling is required. The 30% breakpoint figure is arrived at by calculating wiring costs. Re-wiring a building after it has been constructed and fitted with carpets and desks costs three times as much as pre-wiring a building. Lane claims that fibre optic cable has not been used very intelligently or prolifically, so far leaving a raft of potential benefits untapped. This scarcity of fibre installation is likely to pick up as costs relating to it fall. Once chip manufacturers start to produce chips specifically for use with fibre cable, the boxes needed at each end of the link will grow smaller as well and bring the prices down. The development of a standard for wiring buildings currently being drawn up by the EIA committee in the US is also expected to have a major impact on the whole cabling market. Three standard copper wiring systems have been endorsed to date: IBM’s Cabling System, AT&T’s Premises Distribution System and DEC’s Thin Wire Ethernet system. The combination of falling chip prices and more attention paid to standardisation of cabling should give the user a better deal in the future but short termism of financial controllers could be the sticking point.
