The FDDI standard to create open networking is having difficulty establishing itself – in the meantime could the solution for inexpensive local area networks lie with the yet to be announced TPDDI standard for twisted pair networks? – Sonya McGilchrist finds out.
Despite being heralded as a milestone in the history of networking, since its introduction in 1988, Fibre Distributed Data Interface (FDDI), the 100 Megabit per second standard for fibre optic networking has made very little market impact. Estimates of the UK penetration run as low as 100 installations. Of course there are other fibre optic backbone systems, aside from those based on FDDI – and the route to getting an open system accepted in networking is as thorny as in computing. Although the standard has enticed some big new players into the intebconnecting arena, well established companies already in the field which need to adopt FDDI to make the standard well used have their own proprietary systems to sell, and are obviously keen to maintain those sales for as long as possible. But the other big consideration is cost. Customers have not been prepared to pay around UKP18,000 to install an FDDI bridge compared to the UKP4,000 cost of an Ethernet one. Especially while it is still difficult to hook up FDDI products from several different vendors.
Interop ’90
One of the reasons that FDDI products are so expensive is the huge investment that has gone in to the technology – the electronic components inside an FDDI bridge make up around 75% of its price. But many systems are still not compatible notwithstanding the 37 vendors that managed to link up their systems at the Interop ’90 show. Companies such as FibreNet Ltd, based in Aldermaston, Berkshire, have been quick to exploit the situation. FibreNet says its Magnum 100 proprietary fibre optic ring connects local area networks at 100 megabits per second but at half the cost of using an FDDI system. According to managing director Charles McGregor, the aim of the four year old company is to bring affordable optical backbones to a wider audience. McGregor insists hesupports the introduction of standards and reckons that when the technology settles down and all the major suppliers that claim to be FDDI compliant can actually be interconnected with no problems – perhaps in a couple of years – then prices will drop dramatically. Most industry observers agree. In the meantime,the prospects for the next fibre optic application, fibre-to-the-desk, look rather better than those for backbone FDDI systems.
Fibre-to-the-desk is an extension of the fibre option, so that it is not just the backbone linking Ethernet and Token Ring local area networks: instead, workstations are directly connected to the fibre optic ring. At the moment this type of development benefits high powered workstation users, especially in applications which use up lots of bandwidth, primarily technical and scientific ones. But Sunnyvale, California-based Advanced Micro Devices reckons that software houses such as Microsoft, would make use of the extra bandwidth in non-technical applications such as those using 24-bit colour pictures, if the bandwidth were available. So while proprietary systems continue to plug the gap in optical backbone systems, another standard, TPDDI, is being set up as an open standards route to fast, cheap, local area networking. TPDDI stands for Twisted Pair Distributed Data Interface. It allows for 100 Megabit per second local area networks using not fibre, but ordinary twisted pair shielded or unshielded copper wires. Using copper can cut down the cost of a 100 Mbps local area network by up to 90%. And this reduction addresses a crucial factor in the slow take-up of FDDI, even as a fast backbone option – its prohibitive price. Advanced Micro Devicec is convinced that the future for high speed local area networks lies in reducing costs – implementing copper and bringing down circuit board costs. Its latest chip set for FDDI, SuperNet 2, can drive a complete FDDI station on an AT half-card or similar-sized board, while a fu
ll-size card can accommodate a dual-attachment station. The set can also drive fibre or shielded twisted pair – using the TPDDI standard – without any modification.
UKP100 per link
Advanced Micro’s FDDI marketing manager, Basil Alwan says we are bringing FDDI one step closer to the desktop. BICC Data Networks is one of several manufacturers promoting the TPDDI standard as the link between fibre optic backbones and user workstations. Jeff King of BICC says that although organisations such as financial institutions may still want to use fibre for security reasons – it’s very difficult to eavesdrop on fibre lines – most companies will opt for the cheaper TPDDI copper systems. According to King, in a structured cabling system, single cable point-to-point connections via a concentrator and with one port per workstation, using TPDDI should cost around UKP100 per connection. The corresponding fibre cost is more like UKP1,000. Final specifications for the standard are now being defined by ANSI, the American National Standards Institute, and King is hopeful that for shielded twisted pair, it will be announced next year.
