Tune into the wireless

Wireless networking is a technology that enables two or more computers to communicate using standard network protocols, but without network cabling.

Strictly speaking, anything that achieves this could be called wireless networking, but the industry has chosen to focus on the specific standards-based wireless networking.

The current buzzword, however, generally refers to wireless local area networks (wireless Lans). This technology, fuelled by the emergence of cross-vendor industry standards such as IEEE 802.11, has produced a number of affordable wireless solutions that are growing in popularity with businesses and schools, as well as sophisticated applications where network wiring is impossible, such as in warehousing or point-of-sale handheld equipment.

A world without wires is a seductive promise, but can we stop it from going the way of the paperless office? Wireless Lans have not had a particularly good reputation in the past, and now Bluetooth is the victim of stories that it is both late and plagued by incompatibilities.

Both are increasingly unfair allegations, according to Rene Nitzinger, international product manager for networking products at PC expansion company Elsa. He adds that the battle between Bluetooth and wireless Ethernet may turn out not to have been a battle at all.

"The first 802.11 was not very successful," he admits. "It used three different technologies so there was no real interoperability, and was only 1Mbps. Now there is a new standard called 802.11b which is 11Mbps and fully compatible between vendors at the radio and Ethernet levels."

High-speed wireless
Called 'high-rate wireless Ethernet', the 802.11b standard is maintained by the Wireless Ethernet Compatibility Alliance (WECA), which promotes it using the Wi-Fi logo. Like Bluetooth, it operates at 2.4Ghz, in the licence-free Industrial, Scientific and Medical (ISM) band.

"The wireless Lan makes some applications available for the first time," says Nitzinger. "Wireless is all around us - satellite TV, GSM pagers, wireless local loop. What was missing for a long time was the in-building element."

Typical wireless Ethernet applications include the creation of ad hoc Lans, the linking of portables into a wired infrastructure, and wireless Lan bridging, for example between two offices separated by a road. In a peer-to-peer network, PCs with wireless cards can exchange data directly and without the need for a central hub to co-ordinate connections in smaller environments.

Alternatively, an access point allows them to communicate with the fixed Ethernet as well, via a 10Mbps Ethernet hub or a 10/100 switch port. Internet connection is possible via a fixed or dial-up link: for example Elsa offers access points with integrated ISDN or DSL routers.

"For a laptop, a wireless Lan means you can roam inside the company without losing your network connection," says Nitzinger. "Roaming requires the access points to exchange information over the fixed Lan, but the protocol was not clearly defined in 802.11 so it did not work between vendors. Now, though, you should be able to roam between different base stations."

The problem is it is not cheap. Elsa prices laptop PC adapters at £150 and desktop ones at £200, and though other suppliers offer them for less, they are still far more expensive than ordinary Fast Ethernet cards, and slower. There are savings in other areas, however, because a wireless Lan involves almost nothing in the way of infrastructure costs, with no cabling or hubs to be installed, except perhaps for a central file and print server.

"What we've seen is that 802.11b cards are very interoperable," Nitzinger says. "That's not too surprising because there are only two silicon manufacturers worldwide and we all use a similar media access control [MAC]."

Coping with interference
In addition, although 802.11 includes three physical layer standards, most developers have ignored or dropped the 2Mbps frequency-hopping radio and infrared options in favour of direct sequence spectrum spread (DSSS) radio, which supports one, two, or 11Mbps.

DSSS spreads the signal over several frequencies and can switch channels to avoid interference. It also makes the signal harder to intercept than standard wired Ethernet.

Because it operates on the ISM band, wireless Ethernet is licence-free on 2.5Ghz now and on 5Ghz in the future, although there are power and bandwidth regulations.

"With ISM, one approval covers you Europe-wide," Nitzinger notes. "The disadvantage is that everyone can use it. It needs some tricky RF circuitry to avoid being jammed by other users."

For example, Bluetooth is also on the ISM band, and there are worries about the two interfering, particularly if a single PC has transmitters for both. Fortunately, research suggests that wireless Ethernet will still be reliable.

"Our opinion is that Bluetooth will replace infrared, and that's how we position it," Nitzinger says. "It also gives the choice of combining voice and data. We will be one of the first out with products, with ADSL and cable modems, everything you need to access the Internet. The second will be a USB adapter and then a PC card." Infrared is currently popular for use on devices such as mobile phones, personal digital assistants, printers and on desktop and laptop computers.

Bluetooth vs Wireless Lan?
However, while some have promoted Bluetooth as the ideal way to create ad hoc wireless Lans or connect portables to a fixed Lan, he sees Bluetooth and wireless Ethernet complementing each other rather than competing.

"We see Bluetooth as a wireless Pan: a personal area network, rather than a Lan," he says. "You can use it as a network, but you can't compare it to a real one, and small offices and home offices really need a Lan." On the other hand, 802.11b needs too much power to be used on Palms or PocketPCs, so Bluetooth will be needed to link these devices in.

What will lose out to the combination of 802.11b and Bluetooth will be competitive wireless technologies such as Home RF and HiperLan.

"We see decreasing acceptance of Home RF. It's limited to 2Mbps and stuck somewhere in the middle between Bluetooth and 802.11," says Nitzinger.

He adds that Home RF design is simple, but it is a similar approach to Bluetooth with the disadvantage of being PC-centric.

"HiperLan has more bandwidth by using 5Ghz but the frequency is not unique worldwide," he adds. "Also the chips are expensive and there are range problems - it's almost line of sight."

Trading speed for range
Wireless Lans are built as cells, with several PCs sharing a single access point. In theory, there can be any number of PCs per cell and 64 wireless network adapters per access point, but in practice a maximum of 20 is recommended.

This is because high-rate wireless Ethernet uses the same collision-sense scheme as wired Ethernet, so it faces the same issues of performance falling as the network load increases. There is also the issue of radio noise.

For more than 20 PCs, performance should be better if a second cell is overlaid on the first at a different frequency. But while there are 13 channels available, they overlap to some extent, so you can only have three in a given area that do not overlap.

The other challenge for a radio network is obstacles. A window or a thin wall is not a problem, but a metal or thick stone wall may stop the signal.

Switching to a lower frequency such as 900Mhz brings greater range, but lower bandwidth. Conversely, higher frequency signals give more bandwidth, but can have difficulty passing through even a thin wall.

Data speed also falls with range. Wireless Ethernet can provide 11Mbps at up to 30m indoors or 150m in the open, but falls back to lower speeds when it meets problems. Its range is greatest at 1Mbps, when it can cover 50m indoors, or 400m outdoors.