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The Dual-Band Two-Step

Many of us take for granted the dual- and even tri-band capabilities of our cell phones. My Sprint PCS phone, for example, automatically shifts to analog cellular when I am outside Sprint's digital coverage area. Aside from a beep that tells me I'm roaming, the handoff for basic voice services is transparent.
Wireless LAN users face a similar future as the industry expands beyond the 11-Mbps 802.11b technology that may one day become the equivalent of analog cellular, today's most widely available base service. But implementing multiband wireless systems in a seamless manner will be a challenge.

Many chip developers have thrown their hats into the dual-band ring. Atheros Communications' AR5001X Combo WLAN Solution, which is currently sampling, took home the Best of Interop Grand Prize in May. And Atheros isn't alone: Broadcom Corp., Envara, Intersil Corp., Synad and Systemonic have each announced a dual-band product.

No such product is shipping in volume, but that hasn't stopped some vendors from developing dual-mode access points. Agere Systems, D-Link Systems and Intel Corp., for instance, are offering products that integrate both 11a and 11b functionality on a single access point. Rather than using dual-mode chipsets, these vendors are integrating multiple radios that share a single Ethernet backbone connection in a single box.

Is this a workable solution? In some cases, yes. If, for example, you have a conference room used by multiple departments and perhaps by visitors, installing one dual-mode access point provides flexibility to accommodate both 11a and 11b standards. And because the physical coverage area is confined to a single room, you don't really need to worry about radio-propagation differences between the 11b (2.4-GHz) and 11a (5-GHz) radios.

For more ambitious projects, such as establishing coverage throughout an office building, today's dual-mode products are far from optimal. In my experience, the coverage area provided by enterprise-class 11b access points is at least twice that of 11a offerings -- especially in a conventional office environment. In these cases, the advantage of an integrated access point is limited. To provide full coverage for both 11a and 11b, you'll need to add 11a access points to fill in the dead spots.

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