Dual Mode or Single Mode?

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While 802.11b computing devices and their networks are pervasive, especially in the HotSpot market, support for 802.11a is coming on strong as well. Organizations that can't decide whether to go with 802.11a or 802.11b/g can have both, via products that integrate both 802.11a and 11b/g functionality on a single access point. These products are designed so that their performance is at least as good as their single-mode counterparts. Furthermore, many of these products, rather than using dual-mode chipsets, have integrated multiple radios that can share a single Ethernet backbone connection in a single box.

While dual-mode access points have their advantages, and performance variations among brands of access points are generally minimal, dual-mode APs should not be used in every WLAN installation. A decision first must be made as to whether a dual-mode architecture is a workable solution for the organization's proposed WLAN. To help in the decision-making process, consider the following:

• If the WLAN supports a conference room that will be used by multiple departments then installing at least one dual-mode access point will provide the WLAN the 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/g (2.4 GHz) and 11a (5 GHz) radios.

• If wireless access is needed in areas where there is simply too much interference for 11b/g devices to work optimally, dual-mode access points may be the way to go.

• Dual-mode APs can protect investments in legacy APs while offering the advantages of newer technology; that is, if the long-range plan is to upgrade the WLAN to 802.11a. However, you may want to consider the possibility of bypassing 11a and going straight to 11g, in which case, building a new WLAN around dual-mode technology is unnecessary.

• When designing a network around 802.11a technology: a dual-mode system will allow the organization's employees to take advantage of HotSpots during their travels. (The vast majority of HotSpot technology is based on 11b technology, not 11a.)

For more ambitious projects, such as establishing coverage throughout an office building, the design problems may outweigh the flexibility that dual-mode products offer.

Numerous vendors offer quality, enterprise-class, single-mode access points, but when looking for dual-mode access points, the choice is more limited. Consider products such as Cisco Systems Aironet 1200 Series AP, Proxim Orinoco AP-2000 Dual-Mode Access Point, Intermec MobileLAN WA22 AP, Intel 5000 LAN Dual AP, Linksys WAP51AB Dual-Band Access Point, and D-Link AirPro DI-764 AP.

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