But security isn't the only concern of enterprise IT managers contemplating WLAN deployments or expansions. Limited money and staff mean widespread deployments remain a pipe dream for many IT managers, unless they can prove a compelling short-term return on investment. And then there's the fear that investing in today's most popular WLAN technology--802.11b WiFi--will leave you wishing you had waited just a little longer for a higher-performance system.
That's where 802.11a comes in. Although first approved in 1999, 802.11a has been slow to take off, not only because engineering 11a chipsets is challenging but also because the success of 802.11b has made that system a de facto standard. The landscape changed in 2001, however, when Atheros Communications began volume shipment of its 802.11a chipset. Until then, a war of white papers raged, with some touting 11a as the solution to emerging WLAN performance and capacity problems and others speculating that 11a products would have range limitations of 30 feet. Thus, when we took a look at the first 802.11a offerings, we didn't have high expectations. When the dust settled, we discovered some truth on both sides of the battle line. The best 802.11b products did have significantly greater range than 11a offerings, particularly in walled-office environments. Still, 11a range was better than expected, well in excess of 100 feet in many cases, and 11a was fast.
When we set out, we recognized that the market is still developing. Atheros is still the only vendor shipping 11a chipsets, though we expect to see credible competition emerging in coming months from Cisco Systems, Intel, Intersil and others. Interoperability will become a nonissue in the near term. We also recognized that many of the first 802.11a products making their way onto the market were not targeted at the enterprise. Nonetheless, we thought it was worthwhile to examine what was available, so we invited D-Link Systems, Intel Corp., Intermec Technologies Corp., Linksys, NetGear, Proxim Corp., SMC Networks and Sony to submit their access points for testing. All but D-Link and Sony accepted; neither provided a reason for declining, but since both target the consumer space, we don't consider it a big loss. We conducted all testing at and around our Syracuse University Real-World Labs®.
802.11a: The Details
The secret behind 802.11a is its OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, which offers significant performance benefits compared with more traditional spread-spectrum systems. Both 11a and 11b share a common MAC (Media Access Control) interface, but they share nothing in common at the physical layer except that they both employ radio frequency technology. While 11b systems max out at 11 Mbps (around 5.5 to 6 Mbps effective throughput with overhead), 11a systems offer a data rate of 54 Mbps and a maximum throughput of around 24 Mbps. Most of the products we tested also include proprietary turbo modes that use channel aggregation to boost performance to 72 or even 108 Mbps, but that's clearly a nonstandard offering.
While speed is certainly a compelling reason for enterprises to deploy 802.11a, capacity is an even better justification. Although 11b's paltry 83.5-MHz allocation in the 2.4-GHz band is enough to support three nonoverlapping radio channels, 11a offers much more: The FCC has allocated 300 MHz of the spectrum for unlicensed operation in the 5-GHZ band, 100 MHz each at 5.15 to 5.25 GHz, 5.25 to 5.35 GHz and 5.725 to 5.825 GHz. While regulations vary depending on the frequency channels, that's a lot of bandwidth--enough to support eight nonoverlapping channels, making it much easier to design 5-GHz cellular systems that don't have interference problems. Another big positive--at least for now--is that the 5-GHz band is not as polluted as the 2.4-GHz band, which supports 11b, Bluetooth, cordless phones, microwave ovens, wireless video-surveillance systems--you get the idea.
Whoa There, Cowboy
So why not skip 802.11b altogether and just implement 11a? First, there is the range issue, which means more access points must be deployed so the cost is higher. Second, and more important, there's no easy way to provide backward compatibility with the older 11b standard. Dual-mode access points and chipsets are due to appear later this year, a development that may simplify things, but the transmission range differences between 11a and 11b may still complicate deployment. The most common analogy is Ethernet, which improved from 10 to 100 to 1,000 Mbps, and with each advance, not only was multimode operation key to maintaining backward compatibility but UTP cabling upgrades were needed in many cases. However appealing the potential of 11a may be, you may not need the additional bandwidth for your applications, and there's no doubt that 11b offerings are less expensive and more mature.
Still, by year's end we expect all the major WLAN vendors to offer 11a products, with many offering dual-mode 11a/11b access points that are built using two radios. WECA (Wireless Ethernet Compatibility Alliance) will offer a WiFi5 certification program, which will help ensure interoperability between products based on different chipsets (there will likely be quite a few contending for your vendor's business). After that, we'll begin to see true dual-mode offerings--both access points and client NICs--built around new dual- and tri-mode chipsets that support 802.11a. 802.11b and 802.11g, which offers 54-Mbps OFDM at 2.4 GHz. The emergence of dual-mode clients will make deploying 11a systems much safer because all your client devices will maintain backward compatibility with home and hot-spot networks.
We also expect significant improvements in throughput and range of 11a systems, perhaps as much as 20 percent, in the second-generation chipsets. And we'll see support for enhanced security standards--provided they ever make it out of the 802.11i working group.
The future for 5-GHz WLANs is indeed bright. Unless we can find some way to suspend the laws of physics, you'll need to contend with slightly higher power consumption and decreased range in comparison with 2.4-GHz systems, but that's likely to be a trade-off many organizations are willing to make.
Testing 1, 2, 3
We stayed in the lab to test features, functionality and performance, and we did range and roaming testing in a classroom and office building. Most of the walls in our test site are Sheetrock over metal studs, and most doors are metal. Performance testing measured throughput on an isolated network, with and without WEP (Wired Equivalent Privacy), while range testing looked at not only distance but the ability to stay connected during transit within one access point cell. To gauge roaming capabilities, we placed two access points on different channels but with the same SSID (service set ID), so there was an area of overlap. We then moved from one access point to the other while monitoring the association status. For a baseline we ran tests on an 802.11b Cisco Aironet 350 setup running at 50 milliwatts (half the maximum power), providing a comparison between 802.11a and 802.11b.
Our Editor's Choice award goes to Proxim's Harmony 802.11a Access Point, a system that reflects the company's many years of experience in the WLAN industry (Proxim entered two products, the Harmony and the Skyline; each focuses on different market segments). While far from perfect, Proxim did a much better job than any other vendor in addressing the single greatest concern about 802.11a: transmission range. We went only 140 feet in our test environment before connections dropped--more than 100 feet less than in our Cisco Aironet 802.11b reference test--but the Harmony's range far exceeded that of its closest competitor. In addition, the Harmony's unique two-tier architecture provides significant functional and management advantages over traditional access point architectures.
We also liked the Intermec MobileLAN Access 2106, which is loaded with features tailored toward enterprise environments, but performance and range limitations made it second-best. The only other product we tested that we would consider for large-scale enterprise deployment is the Intel Pro/Wireless 5000, which has a unique software-configurable antenna design and a strong feature set.
The rest of the products are oriented toward single access point home and small-business applications. They all had similar feature sets and performance, and range didn't vary much. Of these products, we liked the SMC offering most and gave it our Best Value award. All these products have significant range limitations, meaning multiple access points must be installed in all but the smallest homes and offices.