The 5 GHz branch of Wi-Fi, 802.11a sounded like a good idea that might never happen. But now vendors are telling us it's a going concern, and analysts reckon its better features should make it popular.

But what do the users say? The main reasons they give for moving to 802.11a are the greater coverage possible and immunity from interference by other equipment.

"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. "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.

Mount Saint Mary College in Newburgh, NY, 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 favours 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."

Dual band makes upgrade easier
Other users find the fact that .11a has a separate band makes it possible to upgrade from one system to another smoothly, or run different services on each band.

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."

An 802.11a network costs more for two reasons. The access points are more expensive, and there has to be more of them, because of 802.11a's shorter range. However, 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's 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."

What about clients?
At first, 802.11a meant different clients, but these too now have combined hardware. Villanova chose Dell laptops as its student standard, with an 802.11a/b/g NIC built in. "We have it set up so the NIC 'prefers' 11a and tries to stay in that band," says John Center, assistant director of network communications. "It will step down to lower data rates to maintain its association and at some point will jump over to 11b automatically if needed."

The school of Electrical Engineering and Computer Sciences at the University of California, Berkeley, deployed an 802.11b/a WLAN based on Airespace products.

"We are primarily 11b, but we do have 11a fully deployed," says Fred Archibald, network manager for the school. "I wanted to be able to offer higher throughput, as 11b doesn't cut it for some of our users when they are copying large files around."

Access points were deployed with specific performance goals in mind. "Our design goal for 11a was to deploy with enough density to deliver a minimum of 12 Mbit/s throughput, not link speed, to every desk," Archibald says. "We've been able to measure this and most desks get 16M to 18M bit/sec or better." (for an idea of the difference between throughput and link speed, read Speed-boosted Wi-Fi isn't all that fast).

In the end, speed is of the essence. While some organisations with 802.11b or even 802.11g have to discourage big file transfers, others are turning to 11a as a means of making WLANs ever more capable. Mount Saint Mary did its initial 802.11a evaluation with streaming video.

"We tuned into Windows Media Server from a half-dozen notebooks," Bucek says. "It's just like TV: We walked all around campus watching it on the notebooks."