802.11a WLANs winning converts
- 06 August, 2004 09:07
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. "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 New York 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 percent of the market this year and next, and dual-band 802.11a and b/g chipsets will jump from 11 percent this year to 22 percent in 2005.
Framingham State College 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 US$240 to US$610, and the combination 802.11a/b/g were priced from US$490 to US$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 Systems 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 US$200 per (dual-band) access point."
The client side
User demand could rise significantly by year-end, when Intel begins promoting its alternative to the Atheros Communications Inc. chipset. The company's dual-band Sonoma package for mobile computers, a follow-on to Centrino, will include the new Dothan Pentium M CPU and the Calexico 2 radio chipset. Calexio will be the first Intel chipset that can use either radio band and thus connect to 802.11a or b/g access points.
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."
When 802.11a products emerged in 2001, "they experienced a boomlet and promptly died," says Abner Germanow, program manager for enterprise computing at IDC. Early products had range problems and were slower to fall in price than 802.11b and then 802.11g, he says.
Because 802.11b and then 802.11b/g WLAN deployments tended to be relatively small, enterprise users rarely ran into bandwidth problems, capacity issues or radio channel conflicts. With 802.11b, users share a data rate of 11M bit/sec and a throughput of 5M to 7M bit/sec, depending on distance. The 11g networks, using the same modulation scheme as 802.11a, boost those numbers to 54M bit/sec, or typically 20M to 25M bit/sec.
But now network executives are extending their WLANs, more users are wireless, applications are more demanding and the executives are considering adding VoIP to their WLANs.
As a result, WLAN infrastructures are being designed with both frequency bands in mind, and sometimes all three WLAN standards. 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 12M bit/sec 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."
A company can choose to overlay 802.11a on an 802.11b network or go with 802.11a/g for brand-new networks, says Philip Solis, a senior analyst with ABI Research. "They're future-proofing themselves," he says.
While some organizations with 802.11b or even 802.11g might 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."