Rhapsody in (802.11)A?

Wireless LAN vendor Proxim Inc. is first out of the starting blocks with a 54M-bit/sec 802.11a product: a CardBus network interface card for desktop and laptop computers.

The card holds a radio that uses the 5 MHz band and is based on the Atheros chipset. It also features a new modulation technique that enables the card to share data up to five times faster than the current crop of wireless LAN products based on the IEEE 802.11b specification (up to 11M bit/sec in the 2.4 MHz band).

The new technique allows for enough bandwidth for medical imaging, big spreadsheets, and large graphics files such as computer-aided design images. And that's great - assuming your users work with medical images, big spreadsheets, and heavy graphics files.

Proxim has added a sweetener, though: some proprietary code that will boost throughput to nearly double the 11a data rate to 100M bit/sec. The drawback, of course, is the card, in this "2X mode," won't be able to communicate with other computers or access points that cleave to the strict 11a standard.

For now, the Proxim 11a card will only let computers wirelessly share data with other similarly-equipped computers, in what 802.11a calls an "ad hoc" network. The computers with the card will not be able to wirelessly link with an existing corporate LAN until Proxim releases the 11a access point in November.

By then, you can expect the start of a flood of 11a access points and interface cards from perhaps as many as 20 wireless LAN vendors. With all those products, there will come a corresponding flood of questions and calculations for network executives and managers:

- Do you deploy the less-expensive 11b LANs or pay more to get the higher-bandwidth 11a products? This may be a tough call. Proxim's 11a card price is US$249 in single quantities. Access points are expected to be roughly $1,000, perhaps a bit higher for premium brands. That's far less than estimates just a few months ago, and prices for both 11a and 11b will continue to fall. But 11a LAN gear will still be, very roughly, about two times more expensive than 11b gear.

- What's the actual bandwidth? In theory, 11a gives you fives times the bandwidth of 11b. But actual throughput will be less: today's 11b LANs, rated at 11M bit/sec, typically give users about five to seven times the bandwidth. Because 11a uses a different modulation technique than 11b, it may be more efficient in its 5 GHz band. But you'll need to make some real world tests to find out.

- What are the actual ranges of the new 11a products when deployed at your site? In theory, the higher band 11a should have a lower range. But if most access points are deployed in practice at less than 100 feet apart, the theoretical difference may be irrelevant.

- What's the power consumption demand of the 11a client interface cards? Depending on how vendors have implemented the electronics, one brand could gulp power from a mobile battery at twice the rate of another. The pattern of use by your mix of users, and the kind of work they do, will affect battery life, too.

As you think all this through, keep in mind a few cautions.

- There's no "migration strategy" between 11b and the faster 11a. You have to physically pull out 11b radio cards and replace them with 11a cards.

- Interoperability of different brands is a promise. Test it. You may find it worthwhile to standardize on one vendor for all access points and interface cards.

- Right now, there's no such as thing as unlimited, or cheap, wireless LAN bandwidth. If you want more, you pay more. For big deployments, the cost of 11a will be high, especially initially.

- Factor in the cost of securing the 11a LAN: authentication, encryption, firewalls, VPNs. Not all sites will need all of these features, but know what your risks are if these protections are missing.

You can expect a symphony of advertising from the 11a vendors. But don't get rhapsodic until you've done the numbers for your actual site.

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