Like all technologies, wireless networking isn't perfect. While deserving much of its recent backslapping, there are a number of important issues every existing or potential wireless user should be aware of.

We continue our two-part feature on wireless networking by looking at congestion, performance, expanding your network and keeping it secure. So ditch those cables and read on.

Congestion and interference
Perhaps the biggest technical issue facing day-to-day wireless networking is interference, either from nearby wireless networks or devices sharing the same radio frequencies.

The 2.4GHz frequency is particularly congested, with 802.11b and 802.11g networks sharing the same radio resources as Bluetooth, microwave ovens, cordless phone systems, baby monitors and wireless video senders.

In the presence of other 2.4GHz devices, the performance and range of 802.11b and 802.11g networks could both be reduced. Similarly, wireless networks could impact on other 2.4GHz devices. Wireless video senders seem particularly at risk, often suffering from audio and video interference in the presence of 802.11b or 802.11g networks.

One solution is to try changing the channel on which your access point or device is operating, but if this doesn't work, you will either have to switch off the conflicting device or swap it for one operating at a different frequency.

Careful channel selection is also essential to avoid interference between nearby Wireless Access Points. While you may believe the 11 to 14 channels of 802.11b and 802.11g provide plenty of scope, each one overlaps with the next.

In fact to eliminate interference, you should select 802.11b/g channels numbered as many as five apart. Consequently 802.11b and 802.11g are limited to just three non-overlapping channels: 1, 6 and 11.

If you have an 802.11b/g network with more than one access point, ensure each is set on a different non-overlapping channel. The same applies to other 802.11b/g networks in range, such as a neighbour or adjacent office.

Consequently to maximise your performance and range you must co-operate with neighbouring networks to avoid using conflicting channels.

802.11a is superior in terms of congestion and interference. First, its 5GHz frequency range doesn't interfere with 2.4GHz devices, although it's worth pointing out that 5GHz wireless video senders already exist in Japan.

Second, unlike 802.11b/g, each of its channels are non-overlapping, which means North American and some European users can use up to eight nearby access points without interference. Again, each 802.11a access point should be set to a alternative channel though, whether it's on the same or different network.

Adoption of Transit Power Control (mandatory for 802.11a in Europe) also ensures each device is only using as much power as it needs to communicate, thereby being more considerate to neighbouring networks.

Performance, speed and range
The prospects of cable-free networking open up all manner of possibilities, but to avoid disappointment it's important to understand any performance limitations.

In terms of speed, most Ethernet networks tend to perform at roughly half their quoted maximum due to protocols and other overheads, and wireless is no different.

802.11b may be described as offering 11Mbps, but from our tests you should expect around 4.5Mbps at best. Similarly, the 54Mbps maximum of 802.11a and 802.11g works out nearer 20Mbps in real-life apps, although we've measured it operating as slow as 10Mbps even under good conditions.

Depending on your wireless kit, you may also experience a further reduction in performance with Wired Equivalent Privacy (WEP) encryption activated.

In our tests with some budget 802.11b access points, we've experienced 10 to 20 per cent performance hits using 64 and 128bit encryption respectively.

While initially disappointing, it's clear all 802.11 standards are more than sufficient for sharing broadband connections, which typically offer speeds of only half a megabit. In terms of file sharing, 802.11a and 802.11g enjoy a three to five times speed advantage over 802.11b, although at best they're still around three times slower than a common wired 100Mbps connection.

While faster file transfer is undeniably good, real-time applications such as audio and video demand specific levels of sustainable performance.

Music fortunately shouldn't pose a problem for any wireless network, with typical MP3 rates requiring just 128Kbps. Indeed, there should be sufficient bandwidth on 802.11b to deliver multiple audio streams simultaneously.

Unmodified bitstreams from a DVD, though, average around 5Mbps and can often peak at 8Mbps, making it unsuitable for 802.11b. Re-encoded material is far more common, with typical videos re-authored to fit on a CD usually requiring no more than 1Mbps.

That said, you shouldn't necessarily expect a smooth ride. Additional users accessing the network will share the available bandwidth, reducing your personal allotment and potentially disturbing your video.

Certainly until the 802.11e quality of service standard becomes available during the following year, wireless networking could cause frustration for streaming media. To play safe we'd recommend anyone wanting to stream video to go for 802.11a or 802.11g, unless they've got modest bit rates and are also likely to be the only user.

In terms of range, figures are dependant on surroundings and normally work out much lower than theoretical maximums. Each installation varies, but during indoor tests with budget 802.11b access points we've measured ranges of around 10m while maintaining maximum speed, or 20m at half speed.

Deployment and expansion
In theory you can place an access point anywhere to build a wireless network, but some locations work much better than others.

For the best range, position your access point roughly in the middle of the desired coverage area and high on a wall away from any physical obstructions.

Also consider hidden joists and what's behind walls, as nearby metal sheets, tanks or girders can impact wireless range. If your access point is built into a wireless router, you may not have to mount the entire thing on a wall - many support external antennas which can be easily positioned.

Every access point has a maximum operating range and number of simultaneous users, but if you need to increase either, simply add extra access points to your network. The use of multiple access points on a single network is known as roaming.

Multiple access points on the same network must share the same SSID name, but be set to different non-overlapping channels to avoid interference.