Network administrators looking into wireless local area network (Lan) technology to improve users' reach, mobility and uptime are in good company - and so are those taking their time about it.

Analyst In-Stat MDS reports that those companies still in the planning stages of a wireless implementation expect completion to be up to two years away.

There are of course immediate trade-offs in adopting wireless Lan technology, the most significant being speed. Cable-based Ethernet offers speeds up to a gigabit, with 100Mbit being the most popular now.

The limitation of wireless spectrum means that such speeds cannot easily be matched by wireless services, with the most common networking standard offering just 11Mbit bandwidth, which is still perfectly useable despite being significantly slower.

"Wireless Lan is still primarily augmentation," explained Zeus Kerravala, vice president of enterprise infrastructure for research firm The Yankee Group.

"There are some vertical market sectors, such as warehousing, where wireless Lan infrastructure has always been popular and will continue to be popular but, in a lot of businesses, people don't move around."

Put simply, few managers ever tear out their networks in favour of wireless.

According to In-Stat MDS, most wireless Lan projects are budgeted below £35,000, and a quarter of large enterprises expect to spend less than £7,000.

Nevertheless, spurred on by the growing corporate use of laptops and PDAs, companies are increasingly investing in wireless Lan access points, to extend the reach of the network quickly and easily.

The simplicity of these devices and their low cost has seen many companies and workgroups invest in these on an ad hoc basis, creating wireless extensions of existing wired Lans outside stated IT policy, itself creating the need for wireless technology to be included within the overall infrastructure of the network.

The mechanics of 802.11b

Most wireless Lans use the 2.4Ghz frequency band. Countries around the world have set aside this portion of the airwaves for unlicensed devices, although they have differing policies on whether such services can be used for commercial gain.

In a typical wireless Lan configuration, a transceiver, called an access point, connects to the wired network from a fixed location using standard Ethernet cable.

Essentially, the access point is the wireless equivalent of a Lan hub. It receives, buffers and transmits data between the wireless Lan and the wired network, supporting a group of wireless user devices.

The access point, or the antenna connected to it, is generally mounted high on a wall or on the ceiling. Like the cells in a cellular phone network, access points can support transfer from one to another as the user moves from area to area.

Access points have ranges from 20 to 500 metres, and a single access point can support between 15 and 250 users on average, depending on the technology, configuration, environmental conditions and use.

It is relatively easy to scale wireless Lans by adding more access points. A wireless access point can track movement of clients across its domain and permit or deny specific traffic or clients from communicating through it.

End users access the wireless Lan through wireless network adapters, in the form of PC cards in notebook computers, or PCI and USB adapters on desktop computers.

Public wireless Lans

Wireless networking initially started out as a private concept, much like wired networking before it. Fuelled by the growth in mobile data services over cellular networks, and the convenience of built-in support for 802.11b interfaces in new operating systems such as Windows XP and MacOS X, operators are now looking to take advantage of the platform for commercial public wireless services.

Already in the US, we are seeing retailers such as coffee shop chain Starbucks implement publicly accessible wireless Lans in its stores. As well as an added value service, Starbucks sees this as a way to retain customer loyalty and draw traffic to its stores.

Here in the UK, BT is set to launch a paid-for public wireless Lan service at the end of this month. About 400 access points will go live in airports, hotels, shopping centres and major business districts offering 11Mbit access to anyone with the appropriate hardware.

This is set to grow to about 4,000 access points nationwide by 2005. However, coverage will be confined to major metropolitan centres and public buildings, meaning that users looking for continuous roaming wireless data access will still need to look at GSM, GPRS and forthcoming third-generation cellular data networks.

BT plans to bill for this in one of two ways: subscription through their BT phone bill, or on an ongoing basis. BT has yet to clarify whether this charge will be per use, time-based or packet-based like GPRS services.

Such a service has been delayed in the UK by regulatory problems. 802.11b uses the public 2.4Ghz spectrum band. Under the rules of the UK Radiocommunications Agency, a public radio band cannot be used for commercial purposes, in the same way that the public cannot gatecrash a commercial frequency.

The Department of trade and Industry lifted this blanket ban earlier this month, allowing the 2.4Ghz band to be used for both commercial and consumer unlicensed data services.

802.11a - the next stage of wireless networking?

With 802.11b firmly entrenched as the popular standard for wireless networking, it is not surprising that the first serious contender to succeed it comes from the same family.

802.11a is a development of the same standard, but using the more plentiful 5Ghz spectrum band. Already in significant use in the US, it is beginning to appear in Europe, slowed by the fact that only a handful of European nations and the UK have actually approved it for use.

A big advantage of 802.11a is that it has 12 separate non-overlapping channels. As a result, you can have up to 12 access points set to different channels in the same area without them interfering with each other.

This makes access point channel assignment much easier and significantly increases the throughput the wireless Lan can deliver in a given area. In addition, interference is much less likely because of the less-crowded 5Ghz band.

A problem with 802.11a is that it isn't compatible with 802.11b or the still-developing 802.11g. In other words, a user equipped with an 802.11b radio card won't be able to interface directly to an 802.11a access point.

In applications where you have little or no control over what wireless cards you'll run into, you'll have interoperability issues.

Thankfully, there are a number of dual-mode access points available from companies such as Intel. This ensures that a move to 802.11a need not render existing 802.11b equipment useless, and that transient visitors to your network, such as suppliers and customers, are supported if they are still using the slower, more common, 802.11b format.

There is also growing competition from other standards such as HomeRF, the main competitor to 802.11b and not a consumer-only technology as its name might suggest.

There is also Bluetooth to consider. While the cable replacement technology is only intended for use over very short distances (up to 10 metres), it is still seen by some as a viable networking standard.

However, adoption has been sluggish at best, and only now are we seeing integrated support and add-on interfaces appear in any great volume. Bluetooth should not be discounted, but is perhaps more suited to removing the need for a cable-based PDA cradle rather than posing a threat to Ethernet.

SUMMARY

• Wireless Lan technology represents a quick and low cost way of extending the reach of an existing wired Lan
• At present 802.11b dominates the wireless Lan market, offering transfer speeds of 11Mbps
• The next step is 802.11a, backed by Intel, which offers an improved rate of 54Mbps using the 5Ghz spectrum.