LOCAL AREA NETWORKS
Contents
Introduction Traditional Community Radio Systems Wi-Fi Type Systems Mesh Type Systems Conclusion
Following the introduction of the Public Switched Telephone Network (PSTN), there developed more local, and much faster, data networks called:
More recently, the development of radio technologies has led to wireless equivalents to these fixed-wire networks, usually for the delivery of broadband services. This paper is concerned with wireless local area networks (wireless LANs), especially in the context of delivering broadband.
Since one of the major technologies delivering broadband in the fixed-wire environment is called Digital Subscriber Line (DSL), sometimes wireless LANS with a connection to the Internet or similar external network are referred to as wireless DSL. However, DSL is a wire-based technology and therefore strictly-speaking wireless DSL is an inappropriate slang term.
TRADITIONAL COMMUNITY RADIO SYSTEMS
The simplest type of community radio network involves a 'hub and spoke' or 'point to multipoint' (P2MP) topology. A base station connected to an Internet service provider (ISP), via satellite or a landline, links to customers through a rooftop antenna. There needs to be a near clear line of sight between the base station and the customer's premises. Such services may have to be licensed if they use licensed frequencies, higher power transmitters or certain types of antenna. Other, less advanced installations may be able to operate in unlicensed bands.
Here in the UK, Firstnet [click here] - an ISP based in Leeds - has a national 3.6-4.2 GHz radio licence and currently offers a service to densely-populated areas around cities, such as Leeds, Bradford, Nottingham, Reading and Coventry. Provided there is clear line of sight, the company can provide broadband services to customers up to 10 km from a base station. Offerings are two-way services at 512 kbps, 1 Mbps and even 5 Mbps. BT - together with an Israeli partner Alvarion [click here] - is also doing a limited customer technical acceptance trail on a P2MP system in Porthleven, Cornwall.
In the summer of 2003, the Government successfully auctioned spectrum in the 3.4 GHz area and services deploying this spectrum could reach up to 25 km from a base station. For the Government, this auction process raised almost £7M. All 15 regional licences were sold: 13 to Poundradio (an affiliate of the Hong Kong-based company PCCW), the northern region licence to Red Spectrum, and the southern region licence to Public Hub.
A particularly interesting new technology goes by the uniquely unattractive name of IEEE 802.11b. It is also known as "wireless Ethernet" or "Wi-Fi" (Wireless Fidelity). It operates in the 2.4 GHz band and, since this is low power, the spectrum is unlicensed. Wi-Fi is a means of providing wireless connectivity in an office (or even a home) for computers (or other devices) within around 50-100 metres (150-300 feet) of a base station. Gartner Dataquest, a research firm, estimates that, in 2002, 15M adaptors and 4.4M access points were sold world-wide for Wi-Fi services.
Wi-Fi has 'taken off' for a number of reasons: it uses unlicensed spectrum and a common standard, it is a well-established technology with a wide choice of equipment, and it is relatively cheap (typically £60 for a card to slip into the lap-top and around £250 for a base station). The only real draw-back is that it has a relatively high power consumption, so that it drains the battery in a lap-top quite quickly. By contrast, Bluetooth technology - another option for connecting devices locally by radio - is not so versatile and does not have the wide range as Wi-Fi, but it requires less power.
An exiting development is the use of W-Fi to enable lap top users to have Internet connection in public locations such as a university campus, an airport, a railway station, a hotel or a cafe. The best-known network of so-called 'hot spots' is the T-Mobile network in over 2,000 Starbucks coffee shops in the USA. Gartner Dataquest estimates that, by the end of 2003, there could be more than 70,000 public 'hot spots' world-wide. It expects this figure to rise to a peak of around 150,000 in 2005, before declining as uneconomic 'hot spots' are switched off.
BT - working with Motorola and Cisco - is opening up its own network of such 'hot spots' through its Openzone brand. By the end of September 2003, there will be 400 sites, with this number rising to 1,000 over the next year through the latest 'hotspot in a box' revenue share opportunities that Openzone is marketing with site owners/retailers. There might be as many as 4,000 sites by June 2004. Another service is called The Cloud [click here] which provides service to 1,000 pubs throughout the UK. BT Openzone users will also have access to this network.
Meanwhile, possibly the most unusual location for one of the UK's 'hot spots' is the beach at Brighton. The next stage is to put Wi-Fi connections on trains and GNER is planning a rollout to all its trains in the course of 2004.
Around the world, city administrations are looking at the idea of ubiquitous Wi-Fi, that is a Wi-Fi service that would be available throughout the community and not just at specific 'hot spots'. Some smaller US communities, such as Hermiston, Oregon and Grand Haven, Michigan, have already installed city-wide Wi-Fi networks. Other larger communities, such as Long Beach, California and Altanta, Georgia, are looking at doing the same. Meanwhile the first UK city to go down this route is Bristol which plans to have the country's largest public wireless network.
Looking to the future, there is a new standard called 802.16a which is supported by a group called the World Inter-operability for Microwave Access (WIMAX) [click here] including Intel and Nokia. This will provide broadband services at much faster speeds (up to 400 Mbps) over much greater distances (up to 50 Km from a base station) without the need for a clear line of sight. This would be wireless metropolitan area network (MAN). However, it is unlikely to appear until 2005 at the earliest.
Another emerging standard is 802.20. This will offer fast (at least 1 Mbps) Internet service to mobile users over quite large areas. Whereas 802.16 standards are aimed at high-quality services, 802.20 is for services with less quality but more mobility.
Wireless systems for industry such as Wi-Fi have mostly used cellular phone-style radio links, using point-to-point or point-to-multipoint transmission, but such traditional wireless formats have limitations in industrial applications, including rigid structure, meticulous planning requirements, and dropped signals
In contrast, wireless mesh networks are multi-hop systems in which devices assist each other in transmitting packets through the network, especially in adverse conditions. One can locate ad hoc networks into place with minimal preparation and they provide a reliable, flexible system that can be extended to hundreds of devices over a wide geographical area.
What mesh networks have in common is that, instead of the current hub-and-spoke model of wireless communications with every device connecting to an overburdened central antenna, any time mesh-enabled devices are in close proximity to each other, they automatically create a wireless mesh network. On such systems, data can 'hop' up to 2 Km from rooftop to rooftop. Among the companies seeking to develop such networking arrangements are the American MeshNetworks and the German Moteran Networks.
However, this technical distinction between non-mesh and mesh systems is not always followed in descriptions of, or discussions about, wireless LANS. Furthermore mesh systems themselves are sometimes said to be either formal mesh, run in an official scheme, or informal mesh, run on an essentially ad-hoc basis.
BT - like many organisations - is interested in exploring the potential of mesh systems. Working with a Cambridge-based company called Radiant Networks, it ran a trial in 2002 of a 28 GHz system in Ponypridd in Wales. However, the trial found the system to be unsuitable for wider deployment. Currently, BT is running a further trial with the British company Radiant [click here] and the trial site is the BT Research Laboratories, Adastral Park, Martlesham. It will use the 5.8 GHz spectrum.
As a robust and cheap technology, Wi-Fi is likely to become increasingly extensive in public locations and private homes to provide high-speed local connection for portable devices such as lap-tops.
More generally, radio technologies such as W-Fi or mesh systems might be the way to provide fast Internet access to rural areas where ADSL or cable modem systems are uneconomic. However, as the geographical reach of ASDL extends, the incentive to develop radio alternatives diminishes and the economics of such systems becomes more problematical.
ROGER DARLINGTON
Last modified 12 August 2004
Links:
Ofcom briefing click here