Over the last year, a new wireless buzzword has grabbed centre stage. Backed by Intel and Nokia, the WiMax standard sounds like the next big thing. Up to 100Mbit/s and ranges of 30 miles. We'd all like some of that, wouldn't we?

Well actually, maybe and maybe not. WiMax has a whiff of controversy (is Intel pushing it for reasons of its own?) and bandwagon-itis (people like Yahoo! are signing up as if it is relevant to them). Let's get to the bottom of what it is, what difference it will make, and "Wi" you should care

Why WiMax?
WiMax covers technology referred to as "broadband wireless access" or "wireless metropolitan area networks" (WMANs), or "wireless last mile". Basically, stuff that links fixed points, using wireless. It's intended for setting up broadband access in places that can't get it, and for making wireless links that take the place of costly leased lines.

A rural site might use it to get link to a centre some miles away that can get broadband access, and to distribute Internet access to local sites. A business might use it to get virtually free bandwidth between offices a few miles apart - free, because once the link is set up, other charges are nominal.

Behind the WiMax brand is a consortium (the Worldwide Interoperability for Microwave Access group) that exists to promote the IEEE 802.16 set of standards. And behind that forum is - mostly - Intel.

There are plenty of other members, including Fujitsu, Nokia and Proxim, but it is Intel that is pushing WiMax hardest, because it wants a standard to promote cheaper wireless broadband access, and a new big market for its silicon.

Like Wi-Fi, WiMax is a marketing campaign for a formal IEEE standard, but despite the similar names these are two very different beasts. Some even question the need for open standards at this level: "You are talking about fixed links set up between devices that can be 10km apart," says Paul Munnery, technical director of Wireless CNP, a UK builder of fixed wireless networks. "Why do we need point to point link to be open system?" Unlike the Wi-Fi hotspot, the WiMax link will only be between two devices, so there's no benefit in making it easy for any number of other devices to link up.

The answer, of course, is that a standard will make for more and cheaper products. Vendors will have to make fewer variants, service providers can be sure that the products they buy will work together, and users should see broadband wireless access provided quicker and more cheaply.

So what is in 802.16?
WiMax' stated aim is to take the sprawling 802.16 set of standards and make them practical, to usher in an era of generic wireless broadband. What does 802.16 cover?

802.16 is an "air interface standard", to define how data is sent over radio links. It was originally intended for a whole bunch of different uses for wireless networking, extending from 2GHz to 66GHz. There are so many possible applications within that range (see our guide, if you really want to know) that 802.16 has to contain a lot of options.

WiMax adds things that formal standards always leave out - conformance tests and tight definitions (sometimes called "profiles") of the standards, designed for specific uses.

Like all IEEE network standards, 802.16 covers the physical layer (PHY) in this case the radio signalling, and the media access control (MAC) technique. These basic parts were created by Task Group 1 of the 802.16 working group.

The physical layer covers such issues as the width of the channels allowed to fit with potential uses. At lower frequencies, line of sight is not important, but at higher frequencies, the aerials must have line of sight, and multipath interference can be an issue. Where appropriate, 802.16's PHY defines forward error correction, and adaptive bursts to make the most of the available signal, and allows time division and frequency division multiplexing.

There's an awful lot of options in the PHY, including those required to allow 802.16 systems to be built which are legal under any country's radiocommunications regulations.

The MAC is defined to work across all the PHY options, and to carry any kind of traffic - including Ethernet, IP, ATM and any other network technology you care to mention. It also does quality of service, so stuff like voice could one day go over WiMax networks.

The 802.16 standard started to include system profiles, laying down what was essential and what was optional to do different jobs with the technology, for instance, running IP or ATM. However, this kind of work is not best done in a standards body, but in a forum, say the WiMax sponsors. The IEEE never finished the profiles, and WiMax is submitting its profiles to the IEEE as it completes them. Some have been approved.

The process has been easiest for the less interesting part of the spectrum, so the 10-66GHz stuff was completed first. In the 2- 10 GHz range, WiMax has to square the IEEE 802.1g spec with the European ETSI HiperMAN specification, and deal with the fact that this chunk of spectrum includes licence exempt bands (2.4GHz and 5GHz) where requirements are different.

The various parts of the 802.16 standard are as follows

802.16a is the part that extended 802.16 from its original range, covering the all-important range from 2GHz to 10GHz, which is where the real action is going to happen in broadband wireless access (see the excitement over the impending ratification of 5GHz in the UK).

802.16c are the system profiles defined for 10-66GHz, including one for IP and one for ATM traffic

802.16/conformance01 a proforma document (known as a PICS) to be used by engineers to specify a system they intend to buy and deploy

P802.16/Conformance02 is basic test suite definitions for 10-66 GHz

P802.16/Conformance03 defines 10-66 GHz radio conformance tests

P802.16d interoperability profiles for 2-11 GHz which have been proposed and will be part of 802.16 eventually.

P802.16e a proposal to allow mobile devices, still at a theoretical level, and potentially in conflict the 802.20 standard proposal

What will happen when?
The big question with any standard is when (and if) it will come into use. WiMax seems to have a lot of support, although no one is predicting an explosion of Wi-Fi proportions.

WiMax products so far are at a very early stage, with 802.16a products from companies like Airspan, that do not yet comply with the newly-minted WiMax profiles, and silicon from companies like Wi-LAN, which claim to be WiMax compliant, but are not yet built into products.

WiMax products should start to arrive in 2004, according to market researcher ABI, and grow to a $1.5 billion market by 2008. At that point, according to a report from Pyramid Research, up to 60 percent of broadband wireless will be over 802.16a WiMax systems. The analyst, John Yunker, warns that service to reach that point, the standard has to get over a hump of skepticism by providers.

In a few years' time, WiMax could be filling the gaps between Wi-Fi and the wired network, and businesses could find it very useful in setting up links a few miles long, or expanding network coverage to otherwise inaccessible areas.

If it fulfils its promise to bring down the cost of broadband wireless, it could well ease the major bottlenecks in today's networks.