Wired on Wireless: A New Class of 802.11 Devices Go the Distance
March 22, 1999
The key development and focus of our tests is the IEEE 802.11 standard. (For more on the specification, see "The Essentials of 802.11" at www.networkcomputing.com/1006/1006r2side2.html.) Years in the making, 802.11 has been criticized by some as too little, too late; too slow at 2 Mbps; too lacking in important details, such as inter-access-point roaming; and too confusing with multiple, incompatible physical-interface alternatives.
The critics have valid points, but they're missing a big one: The 802.11 standard represents a critical juncture for the industry. Because the standard adds legitimacy in the form of true multivendor interoperability, IT managers are taking a closer look at wireless LANs, assessing their potential for applications that can be enabled by untethered, campus-mobile IS technology. With growing demand, wider availability of chipsets and the inevitable hard-nosed competition that characterizes markets for standards-based network technology, prices are bound to fall well below $200 per connection in the next two years. That's a price that invites serious consideration.
Although today's analyses of market share point to dominance by a few major vendors, genuine competition in the wireless LAN market exists. The emphasis on interoperability fostered by 802.11 has product managers getting to know each others' wares intimately, as they carefully try to stake their claims in the early stages of a potentially huge market. Although you won't find Cisco Systems or 3Com Corp. in today's wireless LAN market, you can be certain that will change--probably by the end of this year. Cabletron Systems, Lucent Technologies and Nortel Networks are part of a billion-dollar market, while Symbol Technologies is knocking at that door.
Next come the smaller, but more focused, wireless LAN companies that, along with Symbol, have dominated the vertical markets in recent years. Aironet Wireless Communications, Intermec Technologies Corp. and Proxim also are well-established. BreezeCOM holds a unique position, building on innovative technology and market strength in the interbuilding bridge market. Finally, startups InTalk, MaxTech Corp., No Wires Needed or Samsung Electro-Mechanics each could become tomorrow's leader.
Two Standards for the Price of One Unlike most IEEE standards, 802.11 includes two major physical-layer standards--direct-sequence (DS) spread spectrum and frequency-hopping (FH) spread spectrum. Both operate in 83.5 MHz of unlicensed spectrum in the 2.4-GHz band. Today's installed base is heavily slanted toward FH, but that may be changing. While it is frustrating for the industry to deal with two 802.11 radio standards, there are sound reasons for them. FH systems provide greater scalability and better protection from radio-frequency interference, while DS systems provide about 20 percent better per-station performance and slightly greater transmission range.
Market share favors FH, but a number of forces are beginning to upset the status quo. DS has the lure of a fast-emerging upgrade to the existing 802.11 standard that will deliver a data rate of 11 Mbps. Harris Semiconductor offers a chipset that has been incorporated into an 11-Mbps product line introduced by Aironet. Note that while vendors may tout these products as offering Ethernet speeds, you shouldn't be confused by the difference between data rate and throughput. This technology offers throughput that is only 60 percent of Ethernet's, though it is likely to improve in the future. Nonetheless, there is some marketing magic in that wireless technology can be offered as an alternative--rather than a supplement--to Ethernet.
The major FH vendors, aware of the potential for their favored technology to become a legacy, are aiming their future products at new broadband technology operating at 5 GHz. Until the kinks in that technology are ironed out, Proxim and BreezeCOM continue their exclusive focus on FH, but other vendors with ties to FH--including Aironet, Intermec, Nortel and Symbol--are devoting much more attention to DS. It is likely that some market stratification will occur in coming years with lower-cost, lower-bandwidth products serving an emerging SOHO (small office/home office) market. Proxim, for example, has attracted much attention with its low-cost Symphony product line, aimed squarely at the SOHO market.
Not Quite Plug-and-Play The wireless LAN market revolves around two components: PC Cards for notebook computers and access points (APs), the devices that bridge the wireless and wired worlds. Some vendors offer ISA and PCI cards, as well as station adapters that connect Ethernet and serial devices to wireless LANs. Symbol offers a phone system that is 802.11-compatible. Expect further innovative applications of this technology, including PDAs with integrated wireless LAN capabilities.
The amount of coverage you can expect from a single AP depends on the type of environment and the nature of a vendor's implementation, especially as it relates to radio output power. In open-office, cubicle-style environments, you can easily communicate at distances of several hundred feet. But during our tests in a traditional walled-office environment, we often had trouble establishing connections at 150 feet (see "Our Environments: Testing Transmission Range," page 80). Most vendors offer optional higher-output radios and high-gain antennae for their APs (and sometimes for PC Cards) that let you stretch those numbers.
Given the relatively modest speed and contention-based architecture of these products, distance limitations have a significant advantage: They reduce the number of nodes in a single cell, thereby improving per-station throughput. The down side, of course, is that you'll need a number of fairly expensive APs to cover a large building. Both DS and FH products let you install multiple APs with overlapping cell coverage, but it's easier to implement such an architecture with today's FH products. You simply install additional APs, and mobile units (MUs) will attach to whichever one provides the best signal. DS systems are more complex because you must carefully select non-overlapping channels when designing your cell configuration. This approach limits aggregate available bandwidth and makes installation more challenging. Once the APs are installed properly, MUs can roam between them transparently--as long as all APs are attached to the same IP subnet. Only a few vendors--Intermec, Aironet and Symbol--have focused on roaming across IP subnets, and in all cases, there are limitations.
The Keys to Interoperability Our tests indicate that it may be too early to guarantee interoperability, especially for FH products. With a few exceptions, we were able to get all the DS products to interoperate with relatively little vendor assistance. The situation wasn't quite as smooth for FH products. This has less to do with technical differences between FH and DS than with radio designs and vendor politics. All the DS products we tested were based on Lucent Technologies' or Harris Semiconductor's radio chipsets; each of the five FH products we tested were based on the vendor's own internally developed radio. The same was true, to a lesser extent, with each product's MAC (Media Access Control) interfaces.
While all of the vendors have worked together at the University of New Hampshire Interoperabilty Lab (www.iol.unh.edu), an independent testing facility, we saw vendors engage in some finger-pointing when products didn't work well together. On some occasions, simply adjusting a parameter or two on the AP, or changing the default settings on a PC Card driver, rectified the situation. In other cases, resolution required installation of new software or firmware. Every vendor understands that compatibility with other vendors' offerings is essential, and most have their own testing labs to ensure it. By the end of this year, we expect compatibility to be a nonissue, as vendors begin to fully support all provisions of the 802.11 standard and ship products with default parameters that represent an industry consensus.
Among DS products, Aironet's 4500 series--including its AP and PC Card--emerged as our clear Editor's Choice, excelling in areas such as management and performance. We also liked InTalk's offerings, which provide a range of features at comparatively low prices. For FH, the Editor's Choice was split between Symbol and Proxim, with Symbol having the best AP and Proxim the best PC Card.
Dave Molta is a Network Computing editor at large. Areth Foster-Webster is a network consultant and freelance writer in Syracuse, N.Y. Send your comments on this article to them at email@example.com or firstname.lastname@example.org.
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