802.11a WLANs winning converts

Initially overhyped, then almost dismissed, 802.11a quietly is gaining ground as a wireless LAN standard of choice.

Faced with an array of network infrastructure needs and end-user demand, network executives are adding 802.11a technology to older WLANs or deploying from scratch wireless networks that can support the 54M bit/sec 802.11a and g and the older 11M bit/sec 802.11b.

At sites where these deployments are unfolding, users say 802.11a delivers two critical advantages:

• It runs in the 5-GHz band, free of interference from the crowded 2.4-GHz band used by 802.11b and g (and microwave ovens and Bluetooth).

• It offers 12 to 24 radio channels instead of 802.11b and g's three channels, so you can give far more throughput to many more users.

"Our performance tests with both 11b and 11g proved that 11a was the better solution," says Bruce Burke, network engineer with Pacific Exchange, a San Francisco options trading floor that uses the Airespace WLAN switch and access points. "We simply could not achieve adequate coverage with 11b or 11g." The 5-GHz band freed users from a "harsh [radio-frequency] environment" created by big, overhead stock monitors on the floor.

Big help on campus

Mount Saint Mary College in Newburgh, N.Y., deployed a pure 802.11a network almost three years ago, initially with Proxim Harmony access points and controllers. But now it is starting to shift to Extreme Networks' switch-based WLAN, which supports 802.11a and b/g. The school favors a dense pattern of access points, with relatively short ranges, to ensure high availability and optimal throughput.

"We like to maintain overlap in our access points," says John Bucek, executive director of IT for the college. "I defy anyone to do that with 11b devices, because you have to have them so close together and you run into channel conflict problems."

Building mixed WLANs has gotten easier over the past nine months as more enterprise-class access points and network interface cards (NIC) have come to market with radios that can transmit at 5 GHz for 802.11a and 2.4 GHz for 802.11b and g. Most of these are based on a dual-band chipset from Atheros. IDC says 802.11g radio chipsets for access points will account for 66% of the market this year and next, and dual-band 802.11a and b/g chipsets will jump from 11% this year to 22% in 2005.

Framingham State College in Massachusetts is adding 802.11a radios to its network of Enterasys RoamAbout access points, currently running 802.11b. Each device will have one of each radio. Like Mount Saint Mary, the school is creating overlapping "micro-cells" that will let scores of students in a lecture hall use a WLAN. The network group considered 802.11g but decided against it.

"If you have an access point with 11g, and you have one student connect to it with 11b, then everyone else on that access point has to run at the 11b rate," says Michael Zinkus, the school's director of systems and network services. "And if the [adjacent] access points are on the same channel, you get interference."

Prices and costs

Products that support 802.11a/b/g are more expensive than those for only 802.11g (which can throttle down to work with 802.11b clients). And you need two to four times as many 802.11a radios as 802.11b or g radios to cover a given space.

The 802.11a products are somewhat more expensive than 802.11g or b products. A recent review of online prices for enterprise-class access points found 802.11g-only products were priced from $240 to $610, and the combination 802.11a/b/g were priced from $490 to $1,030.

But 802.11a users say the added capacity and lack of interference are worth the extra money.

"We knew we'd pay additional money for making 11a our standard," says Robert Mays, director of networking communications at Villanova University in Pennsylvania, which has a campuswide 802.11a/b WLAN based on Cisco Aironet 1200 access points. "We thought that 11a speeds were what we had to provide to our users. And the [price difference] is relatively modest: under $200 per [dual-band] access point."