Aironet Turbo DS: Fastest Wireless Yet
February 22, 1999
By Dave Molta
Aronet Wireless Communications' new 4800 Turbo DS Series claims to run at 11 Mbps, breaking the 10-Mbps Ethernet barrier and setting a new performance standard for wireless LANs. Its powerful, manageable platform and elegant form factor signal a maturing market. Yet there's still room for growth: Actual application throughput is only about half the 11-Mbps raw data rate, and the transmission range is significantly less than today's mainstream 1-Mbps and 2-Mbps products. And at $595 for a PC Card and $1,695 for an Ethernet-base access point, the Turbo DS series is quite expensive.
I tested beta versions of the Aironet PC4800 Turbo DS PC Card and the Aironet AP4800 Turbo DS access point in Network Computing's Syracuse University Real-World Labs®. If you're familiar with wireless LAN products designed around the IEEE 802.11 standard, you'll be comfortable with the Turbo DS product line. Like many commercially available 802.11 LAN products, the Turbo DS products use direct-sequence, spread-spectrum radio technology operating at 2.4 GHz. In fact, they're fully compatible with other 802.11 products running at 1 Mbps and 2 Mbps. With a little tweaking, I achieved interoperability between the Turbo DS PC4800 and Lucent Technologies' WaveLAN access point, as well as between Lucent's WaveLAN PC Card and the Turbo DS AP4800. (For more on wireless LAN technologies, see our Buyer's Guide.)
Setting It Up Setting up any wireless LAN product is more complex than configuring products in a typical Ethernet environment, but Aironet has done an excellent job of simplifying the process. When I powered up the AP4800 and attached it to our lab's Ethernet network, it automatically acquired its TCP/IP address and other communication parameters from our Windows NT DHCP server. I then installed the PC4800 in a Compaq Computer Corp. Armada 7800, and when Windows95 detected the new device, I loaded the NIC drivers supplied by Aironet. Because the vendor configures all its products with the same factory-default 802.11 ESSID (Extended Service Set ID)--a parameter that must be consistent for all devices on the same wireless LAN--I was able to establish a connection to the AP4800 (a process known as association in 802.11 parlance).
I transferred an 18-MB binary file via FTP from a Sun SPARCstation 20 in our lab. Although experience taught me never to expect throughput greater than 75 percent of the advertised data rate from wireless LAN products, I was somewhat disappointed to discover that performance topped out at about 5.5 Mbps. For comparison, the same Compaq notebook equipped with a 3Com Corp. 3C562C Ethernet PC Card achieved throughput of 8.8 Mbps and, with the Lucent IEEE 802.11 WaveLAN adapter attached to the Lucent Wavepoint-II AP, throughput was 1.5 Mbps.
So, while the Turbo DS's throughput is nearly four times that of WaveLAN's, it's less than Ethernet because of the increased packet overhead associated with wireless data transmission. However, while the 802.11 product achieves 75 percent of its data rate in FTP throughput and Ethernet achieves 88 percent, the Turbo DS lags behind at 50 percent. Even so, this is the fastest wireless LAN product I've tested.
Distance Matters With the PC4800's compact snap-on diversity antenna, Aironet claims a transmission range of up to 500 feet from the AP in open spaces and about 100 feet in an indoor office environment. Using the signal strength software that ships with the product, I maintained a connection at 70 percent power from an office 100 feet away from the AP4800, and achieved FTP transfer speed roughly equivalent to what I experienced in the lab. As I moved beyond 130 feet from the AP4800, I began to lose association.
Greater distance can be achieved by running the product in multispeed mode, where data rates drop from 5.5 Mbps to 2 Mbps, and then to 1 Mbps. Aironet claims an indoor range of approximately 350 feet when operating at 1 Mbps. Most sites will probably choose to establish cellular coverage by deploying multiple overlapping AP4800s operating on different channels.
Given Aironet's reputation for providing superior management functionality, it came as no surprise that the software driving the Turbo DS series was flexible and feature-rich. You can manage AP4800's out-of-band capabilities using a serial cable or in-band using telnet, a Web interface or via its Windows-based WinDGS software. Although your level of control over AP4800's operations can be overwhelming at first, configuration screens are well organized, regardless of the interface. Likewise, WinDGS or a hardware properties dialog box under Windows9x can handle configuration parameters for the PC4800.
The Turbo DS series uses a CCK (Complementary Code Keying) modulation scheme developed by Harris Semiconductor, so Aironet claims that its products will be upgradable to the IEEE 802.11 standard. (This spec should be ratified this year and will also use CCK.) Aironet also expects to see some future changes in the 802.11 preamble that will increase overall throughput.
Send comments on this article to Dave Molta at dmolta@nwc.com.
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