802.11g Speeds Ahead of IT Needs

To the uninitiated, the evolution of wireless LAN standards might look like an alphabetic soap opera. PC cards and access point hubs based on the 11Mbit/sec. 802.11b WLAN standard were just moving into the mainstream last year when vendors introduced the 54Mbit/sec. technology known as 802.11a. Now vendors are offering a third alternative, 802.11g, which they claim delivers 802.11a speeds over longer distances, while supporting backward compatibility for 802.11b devices—something 802.11a technology failed to do.

But don't rip out that 11b infrastructure, users and analysts say. PC cards and access points using 11g are still immature and provide few real-world benefits today. By this time next year, though, you'll probably end up buying it anyway because the technology will be built into most hubs, or access points.

The benefits of 802.11g derive from the limitations of its two predecessors. Released first, 802.11b uses a transmission technology called direct sequence spread spectrum, or DSSS. Each access point supports up to 11Mbit/sec. over three channels in the 2.4-GHz frequency range. But the technology has a few drawbacks. Having only three channels increases the likelihood of cochannel interference between neighboring access points. And, as with all WLAN technologies, actual throughput is at best only about half the published data rate and drops as distance and the number of users per access point increase. WLANs also face interference from microwaves, mobile phones, Bluetooth devices and even Pentium processors operating in the relatively crowded 2.4-GHz band.

With its higher bandwidth (best case of about 26Mbit/sec.) and up to 13 channels (with 11 more likely to gain regulatory approval in the next two years), 802.11a is a better choice for areas with a high density of users or for applications that require higher data rates. It operates in the less crowded 5.2-GHz frequency band, but it has a shorter range, and its modulation technique, called orthogonal frequency division multiplexing, or OFDM, won't support 802.11b devices. To support both 11a and 11b client types, corporations must buy more expensive, dual-mode access points.

As for 802.11g, it addresses the backward-compatibility issue—sort of. It adapts OFDM to allow 54Mbit/sec. operation in 802.11b's 2.4-GHz band, while supporting 802.11b devices. "It gives you three more channels of 802.11a," says Rich Redelfs, vice chairman of WLAN chip-set maker Atheros Communications Inc. in Sunnyvale, Calif. But does that matter? Probably not, he says, because most corporate uses don't yet require the bandwidth.

"We're having this technology burst that is delivering technologies in excess of demand," says Ken Dulaney, an analyst at Gartner Inc. That's certainly the case at Embarcadero Systems Corp. in Alameda, Calif., which uses pole-mounted 802.11b access points on its loading docks. "Range matters, while our bandwidth requirements are not high," says Chief Technology Officer John Montgomery.

Montgomery says that in a few areas in the yard where workers tend to congregate, having higher bandwidth might be beneficial. The 802.11g standard promises higher bandwidth than 11b, with comparable range. But with current 11g devices based on a draft specification and lacking Wi-Fi Alliance interoperability certification, the decision was a no-brainer: "We will pass on [802.11g] and use 802.11a," he says.

"If you're trying to put these in an indoor office space, range is not an issue," says Redelfs. Network administrators need to maximize bandwidth for each user. One way to do this is to place access points closer together, but that increases the likelihood of cochannel interference, he says. The best solution for 802.11b users in this situation is to move to 802.11a/b hubs. "The beauty of 802.11a is you have so many channels you don't have to worry about interference between access points," he says. Another option for 802.11a devices is to "dial down the power" in order to more closely group access points, he says. The IEEE is working on a standard, 802.11h, that will support adjusting 802.11a power levels and changing channels on the fly to avoid interference with other access points and devices operating in the 5-GHz range, such as radar. But that standard, also called Spectrum Managed 802.11a, is still in committee.

One area where 802.11g could eventually shine is streaming video, says Dulaney. But acceptable quality will require solidification of the emerging 802.11e quality-of-service draft standard, which has progressed slowly in committee. And while video streaming over a WLAN connection may work for home users, today's throughput rates still may not be enough to support it in a business environment, where many users share an access point, he says.

For now, Dulaney says, corporate IT shouldn't get too far ahead of the curve. "Buy b now and then switch over to buying a/g at the end of the year," he says.

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Wireless LANs

802.11 802.11b 802.11a 802.11g
Maximum link throughput 1 to 2Mbit/sec.

11Mbit/sec.

5Mbit/sec.

54Mbit/sec.

26Mbit/sec.

54Mbit/sec.

26Mbit/sec.*
Frequency 2.4 to 2.4835 GHz 2.4 to 2.4835 GHz 5.150 to 5.850 GHz 2.4 to 2.4835 GHz
Transmission technology DSSS, Frequency Hopping DSSS OFDM OFDM, DSSS
Channels per access point** 3 3 13 (24 planned) 3
Date approved 1997 1999 1999*** 2003 (projected)

*802.11g hubs supporting 802.11b clients must run in protected mode, which can cut throughput by as much as 40%, according to Atheros Communications.

**Number of nonoverlapping channels supported.

***Both 802.11a and b specs were approved at the same time, but because of the complexity of 802.11a, b products shipped first. Volume shipments of 802.11a products didn't begin until 2002.

Copyright © 2003 IDG Communications, Inc.

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