DIY wireless networking - Part 1

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Of all the technologies to arrive in recent years, wireless networking is one of the most exciting. Rather than offering mere hikes in performance, wireless changes the way we work, as well as introducing entirely new possibilities.

It's one of those rare technologies that offers something genuinely compelling to both homes and offices. Using wireless, companies can deliver network resources to new employees in every corner of the office with the least disruption.

Homes can share broadband internet connections in every room and even out into the garden without a wire in sight. It's also ideal for situations where cabling is undesirable or impossible - perfect whether you're in a listed building or don't want to snake cables up the landing.

Public areas are also getting in on the act, offering high-speed wireless internet access in cafes, airport lounges, train stations, hotels or even entire city centres.

Indeed, since these are the locations where mobile users often work, wireless networking could eliminate the need for localised 3G mobile services. They could even be used to deliver voice telephone calls over the internet.

Wireless networking is here today and, best of all, it's cheaper and easier to set up than you think. Two PCs on opposite sides of your home could be wirelessly connected for less than £100, while an entire home or small office could be equipped from £200.

The technology that makes it all possible is called 802.11, and we'll be telling you everything you need to know, from its different flavours to deploying products in specific environments.

We also look at security and performance issues and compare other wireless standards like infrared and Bluetooth. In short, you're in the right place to learn how wireless networking could revolutionise your home and office.

Wireless networking may be one of today's most fashionable technologies, but cable-free communication between PCs has been around for some time.

Infrared vs Bluetooth

Most famously, infrared technology has long been used to wirelessly link mobile phones to notebooks or PDAs, or to beam data between portables.

Despite supporting respectable data rates, infrared rarely made it beyond portable devices, and only ever found itself on a handful of desktop products.

Its major limitation for broader use was being a line-of-sight technology, which meant the two devices needed to be pointing directly at each other, and within reasonably close range.

Infrared can only link two devices at once, which, along with its other limitations, resulted in it not being suitable for serious networking.

The trump card held by Bluetooth and 802.11 wireless technologies is radio waves. Unlike infrared, radio waves can freely pass through most materials and walls, and the devices don't need to be pointing at each other.

This allows two devices to remain connected even if one is in a bag, on a luggage rack, or even in another room entirely. Better yet, Bluetooth and 802.11 allow more than two devices to talk simultaneously, and over longer distances at faster speeds.

Bluetooth and 802.11 may both use radio waves (coincidentally at the same frequency), but they're quite different technologies, designed for different tasks, and they also happen to be incompatible with each other.

Bluetooth is designed as a cable-replacement technology, making temporary short-range links between personal devices. As such it's great for connecting phones to headsets, PDAs and notebooks.

Bluetooth may be capable of networking two or more PCs, but as it is limited to one-tenth of the range and speed of even the most basic 802.11 systems, it's almost exclusively used as a replacement for infrared.

The 802.11 technologies are much better suited to networking for several key reasons. First, their range is longer; second, their speeds are faster; third, they support more users. Fourth, and most crucially, 802.11 is simply a wireless version of Ethernet and, as such, can perform exactly the same tasks in the same way as a traditional cabled network.

This advantage cannot be underestimated. 802.11 may allow computers to be connected without cables, but as far as their operating systems are concerned, they're on normal Ethernet networks and already know the protocols and rules.

An Ethernet network, whether wireless, cabled or both, is designed for linking multiple machines, sharing files and other resources, not to mention being left running all day long. The technology works and people are familiar with it.

As part of Ethernet, 802.11 effectively inherits all its benefits and support for existing cabled networking, and hits the ground running. That's why it's the only choice for serious wireless networking and subsequently the technology we're focusing on here.

What are the standards?

802.11 is a family of international standards for Wireless local area networks (Lans) developed and ratified by the Institute of Electrical and Electronics Engineers (IEEE or I-triple-E).

The original IEEE-802.11 standard operated at a frequency of 2.4GHz and delivered maximum speeds of 2Mbps. Since then, several extensions to the original 802.11 specification have arrived, each identified by a single lower-case letter tagged on the end.

The first extension, IEEE-802.11b, increased the maximum speed to 11Mbps and was officially ratified in 1999; we'll refer to it from now on as 802.11b. While the basic 802.11 technology predated 802.11b for some time, it was only the promise of cable network speeds that allowed wireless networking to take off.

802.11b is now the most widespread Wlan standard and, unless otherwise stated, is usually the technology behind what people casually call wireless Ethernet. It can operate over a distance up to 120m outdoors.

A subsequent enhancement to 802.11b, called 802.11b+, doubles the maximum bandwidth to 22Mbps, but to achieve these speeds all devices need to be 802.11b+ compliant.

While initially offering the fastest wireless access, superior and officially ratified technologies have since arrived.

The second major wireless Lan extension was developed in answer to increasing congestion in the 2.4GHz band and desire for greater speeds. IEEE-802.11a operates at 5GHz and boasts maximum speeds up to 54Mbps, albeit over a shorter outdoor range up to 30m; we'll refer to it from this point onwards as 802.11a.

While 802.11a also works as a wireless version of Ethernet, its 5GHz frequency makes it incompatible with 802.11b equipment. Dual-mode devices are available, though, which support both 2.4GHz and 5GHz frequencies, thereby offering compatibility with 802.11a and 802.11b.

Currently in draft specification at the time of writing, but causing quite a stir nonetheless, is 802.11g. This claims to deliver 802.11a's maximum speed of 54Mbps, but on the same 2.4GHz frequency of 802.11b.

In theory, an 802.11g device should work on an 802.11b network and vice versa, offering backwards compatibility with the vast majority of Wireless Lans (albeit limited to 11Mbps), and the promise of higher speeds when paired with other 802.11g equipment.

802.11g is expected to be officially ratified by the IEEE later in 2003, but this hasn't stopped several manufacturers from offering products that conform to the draft specification - many promise free upgrades should the final standard be different.

Knowing your Wi-Fi

Devices that conform to the same 802.11 standard should work together, but in practice you may find some combinations are incompatible or cause a reduced quality of service.

The Wireless Fidelity (Wi-Fi) Alliance was formed in 1999 to offer independent certification of interoperability between 802.11 products. If a product has the Wi-Fi badge, it's guaranteed to work with other Wi-Fi-certified equipment.

Wi-Fi-badged products are by no means a necessity for a decent wireless network and the cost of certification has discouraged several manufacturers of budget products from bothering.

ome others don't see the point in certifying new products based on chipsets that have already been certified on other models. That said, the Wi-Fi badge has been marketed well and most manufacturers now realise it's one of the first things customers look for.

Consequently, while Wi-Fi certification is not mandatory it's becoming increasingly common.

The Wi-Fi alliance started by certifying 802.11b products only, but recently began certification of those conforming to the 802.11a standard; it is also expected to certify 802.11g products once the specification has been ratified by the IEEE.

With both 802.11b and 802.11a products receiving certification, and 802.11g only months away, the original plain Wi-Fi badge is clearly no longer sufficient to guarantee two products will work together.

To cope with the increasing number of standards, the Wi-Fi Alliance has extended its badge with a newly designed 'capabilities' label which currently features a pair of tickboxes, indicating support for either 2.4GHz/11Mbps or 5GHz/54Mbps.

While these differentiate 802.11b and 802.11a products, a third option will presumably be required to identify the 2.4GHz/54Mbps of 802.11g; only time will tell. For more information on the Wi-Fi Alliance, check out www.wi-fi.org.

Wi-Fi performance issues

Wireless technology may solve many problems, such as how to deploy a network where cabling is inconvenient or impossible, but at the same time it creates many issues.

Problems to be aware of include range, speed, radio congestion and compatibility. Range and speed are intrinsically linked, with the 802.11b specification claiming a range of 120m outdoors at its top speed; moving indoors halves this to 60m.

All 802.11 standards are also capable of reducing their performance as conditions get worse, which in theory could extend the ranges further; you'll often see claims of almost half a kilometre outdoors using 802.11b devices running at 1Mbps.

As with all radio devices, though, an awful lot depends on the surrounding environment. Buildings, trees and cars, along with walls, furniture and people all take their toll on the range and speed.

Congestion from nearby wireless networks, or other devices sharing the same frequencies can also reduce performance.

Before you think radio congestion doesn't apply to you, remember the 2.4GHz frequency of 802.11b and g is also used by Bluetooth, cordless phones, wireless video senders and microwave ovens - and these don't have to be in your own home or office to leave their mark.

So what can you expect in practice? In our indoor tests we've found an average 802.11b network should deliver its maximum speed across a radius of 10m, and this includes passing through several thin walls.

Introduce thicker walls and longer distances and you'll see performance fall. Again in our tests we found the maximum indoor range of an average 802.11b network, once a couple of thick walls were in the way, was around 20m, and beyond this distance the speed normally halved.

In terms of speed, most networks tend to perform at roughly half their quoted maximum due to various overheads. For example, a 100Mbit wired network may deliver no more than 60Mbps in practice. In our tests with 30 different combinations of 802.11b products, wireless was no different.

The average speeds we measured between 802.11b devices worked out between 3.5 and 4.5Mbps, and this was with the OS reporting a perfect 11Mbps connection.

Adding more users further reduced the performance in our tests with budget equipment, with just one extra connection dropping the speed of both by around 10 per cent. Activating 64bit or 128bit Wired Equivalent Privacy (Wep) encryption further reduced performance by around 10 and 20 per cent respectively.

In our tests 802.11a and 802.11g products were pretty much neck-and-neck in terms of speed, but delivered just under 10Mbps to one user without encryption - only around three times faster than we measured with 802.11b.

This is still twice as fast in practice as USB 1.1 and 10Mbit cabled Ethernet, so if you want to see the benefit of 802.11a or g adaptors, you'll need to connect them to sufficiently fast cabled networks or desktop interfaces. Notebook users with PC Card adaptors will need Cardbus slots for 802.11a and g.

While 802.11g matched the speed of 802.11a in our tests, and worked over a much longer range too, it currently has one big Achilles' heel. By introducing just one 802.11b device to an 802.11g network, we saw the latter drop to 802.11b speeds and therefore lose its benefit entirely.

802.11a may not offer backwards compatibility with 802.11b and g, but at least it's not disrupted by either of them. 802.11a is also likely to perform better under heavy loads of multiple users, which makes it more suitable for larger businesses wanting to expand.

The biggest caveat for 802.11g, though, is that it and the products we tested were using the draft specification and, while the final standard is not expected to have any changes, we have to reserve judgment until official ratification.

If it reassures potential investors, however, Apple's already announced it will use 802.11g for its latest wireless products, and many other early releases also offer free upgrades should the final specification differ.

Maximising performance

There are several things you can do to maximise the potential range and performance of a wireless network, but the single most effective one is ensuring the antennas have as clear a path between them as possible.

This can be tricky on the client side, especially with internal PCI Card adaptors which might be at floor level. Some cards or adaptors allow antennas to be connected on cables for better positioning on desktops or even higher on walls.

If your network uses a wireless access point (Wap) through which all devices connect, the ultimate priority is to position it high in a room, away from obstructions and roughly in the middle of the area of desired coverage.

Remember that obstructions, such as metal sheets or girders, could be hidden in a wall or ceiling, so consider your potential locations carefully.

Should a single access point be insufficient to cover the required area, you can easily install extra units to extend the range.

In such cases, each should be connected to the same router or hub and configured to share the same Service Set Identifier (SSID) but set to operate on different channels, preferably at least two apart. Fitting additional access points will also allow more users to be simultaneously connected.

What about congestion?

One of the biggest surprises for anyone setting up their first wireless Lan is discovering they're not alone. An initial snoop could reveal numerous other wireless Lans within range, all competing for limited bandwidth.

While this is a huge issue for business districts, it's also becoming a concern in domestic environments.

Fortunately the 802.11 specifications allow operation on a number of channels, and for the best performance, you should run your network on a different channel to those nearby - ideally two or more channels apart for 802.11b.

Setting the operating channel is as simple as entering a number into the supplied networking software, and many can also automatically sniff around for the most suitable one.

Conducting a site survey is essential for anyone in a built-up area to discover nearby networks, available channels and the most suitable locations for antennas. Clearly this could prove especially tricky if you're using multiple access points on different channels.

As wireless networks become increasingly widespread, you may have to run yours on the same channel as one nearby and accept both will suffer from reduced performance.

The only other alternative is to use a less congested frequency, such as the 5GHz band of 802.11a. Many networks are deploying 802.11a purely out of congestion necessity, and view its increased speed simply as a bonus. Again, the reduced range of 802.11a also makes it attractive in terms of potential congestion.

We performed a congestion test by making a call with a Dect cordless phone in the same room as an 802.11b network and found it made no difference to performance.

The situation may be different in an environment with multiple 2.4GHz devices such as video senders and Bluetooth, or in a call centre with hundreds of cordless headsets.

The biggest problem with congestion seems to be nearby wireless networks operating at the same frequency and, worse, on conflicting channels. Again, the only solution is to move to a different frequency, or to build a traditional cabled network instead.

Finally, in terms of interoperability we've found few if any problems getting wireless kit from one manufacturer to work with another.

In our tests with no fewer than 30 different combinations of 802.11b devices, each communicated without a hitch - and this included combinations of both Wi-Fi and non-Wi-Fi-certified products, which proves you don't necessarily need the badge for interoperability.

It was also reassuring to see early 802.11g products work with existing 802.11b kit, although to enjoy the full speed of an 802.11g network it looks like 802.11b devices may have to be excluded.