Buyers Guide

There's Relief Ahead For Your Wireless Woes

There's no doubt that wireless LANs are cool. But is this just another overpriced, exotic technology? Is it stable enough for real applications? The answers are a qualified "no" and "yes," respectively. Wireless LANs today are, for the most part, a niche market, dominated by installations in health care, retail and warehousing. Total annual U.S. sales of wireless products are less than $200 million. However, this is a technology that may be breaking out of its shell, spurred by technological improvements and standardization efforts. The Yankee Group, a market research firm, predicts that the market will expand to more than $1 billion by the year 2000.

For that to happen, a number of developments w ill need to occur. First, standards-based products will have to be released into the market. Standar ds will precipitate the "commoditization" of certain components, thereby significantly reducing prices and attracting the attention of IT managers who insist on standards-based network technologies. The Institute of Electrical and Electronics Engineer's (IEEE) 802.11 committee has been working for some time to craft a wireless LAN standard, and although this process has been delayed by technical obstacles and vendor politics, standards may be at hand during the next several months. Many vendors are shipping products based on 802.11 draft standards, and major suppliers are producing chipsets that will make it easier for others to get into the wireless game.

Once the industry overcomes the standards obstacle, network engineers and IT managers will need to become more familiar with the product selection, implementation and support issues before we see widespread adoption. Groups such as the Wireless LAN Alliance (see "Wireless LAN Alliance Touts Its Image," page 126), have begun this process by disseminating technical information and case studies related to wireless LANs. As the market expands, systems integrators will respond by offering services to assist customers with implementation.

What's Your Poison? There are two primary applications of wireless LAN technology in today's market: intrabuilding wired LAN alternatives and building-to-building LAN interconnect systems. Most of the market hype involves the replacement of traditional Ethernet and Token-Ring LANs with wireless systems. The simplest solution is peer-to-peer wireless, which lets two devices connect and share resources without cabling. This setup can be useful, for example, in allowing a user to synchronize files between a desktop and a notebook computer or in a temporary office where users need to share data. More typical is using wireless technology to supplement an existing wired LAN or access points to bridge between wired and wireless worlds. These access points, which typically sell for $1,000 to $3,000, include a wireless rad io and antenna as well as a wired LAN interface, usually Ethernet, and bridging software that buffers data, limits the broadcast of unnecessary traffic and deals with other specific properties of wireless LANs. The wireless devices normally run a derivative of Ethernet's Carrier Sense Multiple Access (CSMA) protocol, but incorporate collision avoidance rather than collision detection. Access points are connected to the Ethernet LAN and spaced throughout the facility to provide adequate geographic coverage.

Wireless LAN interface cards are available for desktop and notebook computers. Some vendors offer traditional ISA adapters with a jack for an external antenna, or a wireless transceiver that plugs into an existing Ethernet card. But the most common offering is a PC Card interface designed for notebook computers. An antenna connects to the PC Card and attaches to the case of the notebook computer. Significant efforts have gone into minimizing the power consumption of PC Card radios. These devices commun icate to the access point, which provides an interface to the wired LAN infrastructure.

The distance a user can wander from an access point (or another node in a peer-to-peer configuration) depends on a number of factors, including wireless transceiver and antenna design, electromagnetic interference and the physical composition of the facility. Wireless devices can use radio or optical communications technology (the former is more common).

The use of wireless technologies for building-to-building connections has a history predating the implementation of wireless LANs. Traditional systems have been based on high-frequency, narrow-band microwave transmissions. Although these systems are somewhat costly and require an FCC license to operate, they offer extremely high levels of performance and reliability. Recently, lower cost alternatives based on spread-spectrum radio or infrared technologies have gained popula rity in the market. The spread-spectrum building-to-building links use radios identical to their intrabuilding LAN counterparts. High-gain directional antennas are used for communications at distances up to 25 miles, providing very high reliability--often better than conventional microwave even under adverse weather conditions. Bridges or routers are installed at each end of the wireless link to act as an interface between the wireless network and the wired LAN infrastructure. These systems typically operate at speeds of 2 Mbps, making them ideal alternatives to leased T1 lines. Newer systems are beginning to appear that provide communications speeds of up to 10 Mbps.

Infrared systems represent somewhat more of a niche market, probably because they impose more restrictive distance limitations and are more susceptible to service interruptions attributable to heavy rain. On the other hand, the infrared systems do offer high levels of throughput. They are an excellent choice for interconnecting buildings in a campus setting where long-distance coverage is not a factor.

Wireless Design Alte rnatives Spread-spectrum radio is the dominant wireless system in today's market, and two major designs dominate vendor offerings: direct sequence and frequency hopping. Direct-sequence designs use a chipping code to generate a random pattern for each bit transmitted. Frequency-hopping designs use a narrow-band carrier that changes frequency in a pattern known to the transmitter and receiver. Although direct-sequence systems have offered the best throughput, frequency-hopping systems are becoming more popular.