Let there be light

January/February 2002 Fast overcoming a reputation for unreliability in bad weather, free-space optic network operators are finding that wireless laser technology can fill crucial gaps in a variety of applications

Cablefree's FSO solution in use in the metropolis

Coursing through the thousands of miles of network arteries that entangle the globe, it is light that provides the pulse of the telecoms revolution. The information sent through carriers' fibre-optic networks is generated by lasers flickering on and off - as often as ten billion times a second. While the impact of this optical technology on long-distance communications is well documented, parallel systems are now making their presence felt in another fast-growing technology sector, that of wireless networking.

The established complex installations of enterprise and SME business networks are increasingly being complemented with wireless technologies such as 801.11b or WiFi, which transfers data over short distances at speeds comparable to conventional Ethernet-based networks. Despite some ongoing, but solvable, concerns over security implementation, wireless networks carry obvious benefits, including the ability to build or extend a network more quickly and cheaply - and therefore with greater spontaneity.

Cablefree's FSO solution

Wireless laser systems, typically referred to as free-space optic or FSO, build on these assets to enable wire-free networks to be established on a campus-wide basis. The principle of an FSO connection is simply to position two laser-based modules in direct line of sight of each other, which allows them to relay data over a projected light beam.

The modules are typically mounted on the outside of buildings, although the beams are capable of passing through glass to an interior receiver. FSO installations are also capable of impressive data transfer rates - up to 2.5Gbps - and the technology is well-established. Yet it is only recently that FSO's proponents have won a great deal of attention.

top

'Nobody needed this gigabit technology in 1997,' suggests Stephen Patrick, chief technology officer at Cablefree Solutions, a firm that manufactures and installs FSO solutions. The market is currently worth around ¤111.9m million a year, but analysts at Merrill Lynch predict booming demand will see the FSO market grow to ¤2.23 billion in five years. By comparison, IGI says the radio-frequency wireless market will be worth ¤19 billion in 2005.

As with short-range wireless systems, FSO offers fast and cost-effective installation: it need take only an afternoon to get a network up and running. That factor alone has seen FSO enjoy success in niche markets like broadcasting and motor racing, where high-bandwidth networks often have to be set up at short notice or on a highly temporary basis.

Patrick points to Formula 1 as an example, explaining that, at each race event, teams have to create networks relaying car telemetry. 'The networks have to reach across the pit lane to the garage. Our clients' previous solution was to lay down amoured fibre; now they literally plop tripods down.'

A further, darker example of FSO value for creating spontaneous networks came in the wake of the September 11 attack on the World Trade Centre. Syntelco used FSO equipment from LightPointe to establish a network link equivalent to two T-1 lines (1.5Mbps per line) within four days of the attack. The link was used to serve the Federal Emergency Management Administration offices.

The disruption to lower Manhattan was such that two weeks later, an estimated 10,000 people in the area still lacked a telephone connection, but canny enterprise firms in the area were able to use FSO installations to quickly re-establish links. 'We're seeing more interest because this event has put more emphasis on how the technology benefits customers,' says LightPointe CEO John Griffin.

top

Atmospheric conditions

Like the infamous incident of UK high-speed trains being delayed by leaves on the track, FSO's nemesis lurks in the variety of weather conditions it must operate in, affecting the ability of air to conduct the signal. Although a single connection can operate over distances up to 4km in optimum conditions, CableFree's Patrick readily confesses that something as innocuous as fog can greatly reduce that limit.

'Attenuation is a factor,' he says. 'The relationship is the size of the water drop versus the size of the signal's radiation - similar to the way rain on your windscreen scatters light. When the two sets of particles are similar sizes, you have a problem. Microwave has similar issues with rain.'

Reflections from settled snowfall can also have an impact. 'You wouldn't want to run above 2km in places like Poland and Scandinavia. In Africa, where there isn't the thick fog that you get in Northern Europe, we have installations at 4km,' he says. The impact of atmospherics can be lessened, somewhat, through technology and ongoing R&D, but ultimately, says Patrick, FSO providers must be realistic about what their equipment can achieve.

'You can transmit extremely high data rates, but you can't penetrate certain types of atmospherics. We've had to be careful that we didn't oversell the technology. Typically customers want 'four or five nines' of network availability - 99.999% - so you need to provide customers with planning tools so they can decide the maximum distances to achieve that. By focusing on where the technology does work, we've provided excellent availability.' Although different manufacturers make different claims, the real-world performance of FSO in European environments is typically 500 to 700m for Gigabit transfer rates, and 2km or so for 155Mbps.

FSO is also regarded as a safe technology: its Class 1M rating means there are no licensing issues, and the theoretical risk of damaging one's eyesight by staring into the light beam is easily avoided, says Patrick. 'By making sure the beam is fat and round, the power is diffused, so it's impossible to get it all on the retina.' And while radio-frequency wireless firms address customers' well-publicised concerns over hackers accessing networks with little more than a laptop and a degree of knowledge, FSO beams are impossible to intercept in this way.

top

Market conditions

While niche markets like Formula 1 add glamour, it is the enterprise market that makes the bulk of FSO purchases, says Patrick, especially for bread-and-butter applications like campus-wide LAN connections and telephone switchboard networking. 'Planning is very simple,' he says. 'You can upgrade networks with simple module swaps, and you get a tangible asset that you can take with you. We think FSO will be used for SME connections in the next year or so.' Maintenance costs are also attractive: all that's typically required is to clean the laser lenses every few years.

The area that Patrick predicts is set to grow rapidly in the next few years, however, is the service provider sector. 'The providers we are working with, such as cellular providers, use FSO to fill a blank spot in their coverage, especially in cities,' says Patrick, adding that future demand for 3G technologies will place a greater strain on radio-based services. 'The bandwidth demands between cell sites are much higher with 3G.'

The speed with which FSO links can be established could also offer a solution to the ongoing issue of providing affordable and fast 'last-mile' connections to residential customers. FSO equipment providers are working on ways to serve multiple points from one source. FSO can also be used to 'lock in' customers by offering them an immediate link enabling the carrier to gather revenue immediately. 'As soon as the bandwidth goes up, no one technology can serve all customers,' says Patrick.

top

top