Bluetooth no rival for wireless LANs

The actual similarities between Bluetooth and 802.11b wireless LAN (WLAN) technologies extend little beyond the word "wireless" and a shared use of the 2.4GHz waveband, despite much confusion between the two. Most industry experts believe they will be complementary rather than competitive.

Casual observers might look at Bluetooth's speed and brand it as "a poor man's 802.11", ignoring the fact that Bluetooth is designed for a different range of applications than most WLAN technologies, and so has a different set of strengths.

But despite its lower bandwidth and shorter range, Bluetooth devices may compete with WLANs in some areas, such as the secure delivery of low-bandwidth applications like email and messaging to handheld PCs, and could even create private, low-cost mobile phone networks.

The main reason why most IT managers reject Bluetooth as a WLAN technology is its low data rate. Each access point provides a bandwidth of just 721kbit/s, while 802.11b can reach speeds of 11Mbit/s, although 5.5Mbit/s is more usual.

Another snag is the users that Bluetooth can support. Each device - including network access points - can maintain links with no more than seven others simultaneously. Access points based on 802.11 can handle up to 64 users in theory, but usually cope with 32 in real-time environments.

Range can also be a problem. The next generation of Bluetooth access points will be able to handle signals at up to 100 metres, but most Bluetooth clients will still have a maximum range of 10 metres. All 802.11b devices - both access points and client devices - can communicate over distances between 50 metres and 100 metres, depending on obstacles such as walls or ceilings that block a clear line of sight.

What makes Bluetooth far more suitable for integration into handheld PCs and mobile phones is its much lower power requirements. It also has built-in quality-of-service (QoS) capabilities that make it better suited to carrying voice calls. Firms deploying Bluetooth access points could implement an internal mobile phone network and patch that network into their private branch exchange (PBX), for example.

"Ideally, firms want [mobile staff] to have a mobile phone or PDA that connects via GSM in the outside world but switches to Bluetooth within the office," said Mike Wilson, chief executive of Red-M, a maker of Bluetooth network access points and wireless servers. Wilson estimates that this arrangement could cut the cost of corporate telephone bills by up to a quarter.

Bluetooth also appears to handle security better than 802.11. "Bluetooth is far more secure than 802.11 in that it has embedded frequency hopping, and communicating devices need to be bonded using unique IDs before they can connect," said Wilson, adding that Bluetooth access points will also provide virtual private network (VPN) functions in future.

While Bluetooth networks can be complementary to WLANs, this raises the critical issue of interference. Both types of device transmit data signals in the 2.4GHz radio frequency waveband, and interference can reduce levels of bandwidth and even block connections completely.

"Across a desk, a Bluetooth-enabled handheld and 802.11b-enabled PC would see a five to 10 percent performance degradation, but the user wouldn't notice it," said Wilson, who recommended that transmitting devices should be at least 9in apart.

"It depends on the proximity of devices," agreed Scott Ruck, enterprise product manager at WLAN equipment manufacturer Proxim. "Most users will see interference result in a throughput hit, but it can cut the link completely."

Recent IT Week tests found that putting Bluetooth and 802.11b devices close together could cause transmission rates to drop by as much as a third, though no loss of network connection was observed.

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