FSO challenge to fibre to the home


Free Space Optics (FSO) is increasingly being deployed to provide high capacity connections in metro and campus environments.

Free Space Optics (FSO), also known as optical wireless or fibreless optics, is increasingly being deployed to provide high capacity connections in metro and campus environments. The key properties of light, modulated and directed through the atmosphere, rather than fibre, enables wireless connection of voice, data or video with fibre-like bandwidths. Vendors such as CableFree Solutions offer point-to-point transfer rates from 1Mbit/s to more than 2.7Gbit/s with ranges up to 4km. Interface options enable transmission of voice, data, and video signals in a variety of applications.

Never mind the weather
Early attempts at FSO, which actually pre-dates the fibre-optic era, were dogged by poor reliability in adverse weather conditions such as fog, and over-optimistic range claims. The insatiable demand for bandwidth by business and residential users has forced a re-think about network strategies. FSO technology has evolved, with the hallowed "five-nines" (99.999% availability, whatever the atmospheric conditions) being achieved over moderate distances, with stringent eye-safety requirements also being met.

Enterprise and campus networks employ FSO links for building-to-building connections. Compared with leased lines, FSO offers lower costs and higher bandwidths; true LAN-speed backbone extensions remove the bottleneck and complexity of routed solutions over slow leased-lines. There is no need for frequency licenses or risk of interference. The technique also enables users to own the infrastructure, and to deploy Gbit Ethernet as a LAN backbone, where FSO and fibre optics are the only viable alternatives.

Traditionally, many types of service providers have needs that can be met by FSO. National service providers have used copper leased lines, or licensed microwave radio to provide access from a backbone SDH fibre ring network to customer premises. FSO can either replace these, or work in tandem to provide greater resilience and faster connections.

Internet service providers can employ FSO to offer "faster than xDSL" ultra-broadband connections to large corporate customers, and temporary provisioning of circuits for short-duration events. The new generation of competitive local exchange carriers often operate in collaboration with building owners to broadband-enable multi-tenant business buildings. Cellular network operators are also major users of FSO where, in densely-populated cities, micro-cells are deployed either to fill in weak spots in coverage or to alleviate congestion.

Meeting future demands
There is clearly no panacea for today's telecom access network problems; many xDSL roll-outs have been hit by poor quality copper networks and range limitations. Microwave links, which depend on suitable roof-top locations, can face public resistance in urban areas. Fibre-digs are expensive, slow and require planning permission. The much-discussed fibre-to-the-home solution has so far seen little uptake due to the excessive cost and disruption entailed. In cities such as London, busy streets are already designated "full" where there is no room for new cable ducts. Even in the USA, fewer than 5% of business buildings are fibre connected.

FSO, having existed as a niche technology for several decades, has now truly come of age. Major network providers, facing increased competition and bandwidth demands, are actually deploying, not just trialling, FSO "live" to connect customers to their networks.

Developments such as 10Gbit Ethernet will ensure parity of FSO with fibre networks; point-to-multipoint and low-cost "self-installing" FSO terminals will offer small businesses and even residential broadband connections. Acknowledging limitations on range and line-of-sight, FSO certainly is joining mainstream fibre, copper, radio and microwave techniques, which together can fulfil the network dream: cheap; safe; and reliable fibre-like bandwidth, everywhere.

Stephen Patrick, director and CTO, Cablefree Solutions, Hampton, Middlesex, UK

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