Wireless bandwagon rolls for LANs as well as WANs.

With the growing popularity of mobile computing has come an explosion of wireless links--at least for wide area networking. Within buildings, though, the anticipated wireless revolution has stalled, undone by high costs, slow speeds, a lack of standards and concerns over security of radio transmissions.

A few years ago, wireless LAN vendors promoted their products as a less costly and a more convenient and flexible alternative to pulling cable to connect computers. What they didn't foresee was the emergence of inexpensive wiring options and the dramatic drop in prices of Ethernet cards. Also, wired LANs have been able to adjust to the ever-faster speeds demanded by multimedia and other bandwidth-hungry applications.

Meanwhile, users have been reluctant to embrace the proprietary wireless LAN offerings, which restrict them to a single vendor. As a result, wireless LANs have fallen well short of the rosy projections made for their growth.

Cost has been a major hurdle. The Yankee Group, a Boston market research firm, estimates the average cost of installing a wireless LAN at $1,107 per user, compared with $780 and $880 for Ethernet and token ring LANs, respectively.

Disputing the cost disadvantage, proponents of wireless LANs point out that organizations typically move 25% or more of their LAN nodes each year. When you factor in these expenses with the wired LANs, they claim, the lifetime costs become comparable. Opponents counter that most organizations plan for such moves by installing wiring to all points where offices and cubicles are likely to be, so the expense is minimal.

Speed is more clearly a constraint with wireless LANs, but even here the vendors are making progress. Until last year, 512 kb/s was the maximum data rate. Since then, the speed has even increased, first to 1 Mb/s and more recently to 2 Mb/s.

What's more, the IEEE 802.11 committee recently moved closer to a wireless LAN standard by adopting a physical layer specification presented by Proxim, Inc., a wireless networking firm based in Mountain View, Calif. The committee had already accepted a proposal for a common media access control (MAC) protocol last year, and it now expects to have a complete standard by year's end.

Proxim's specification allows users to transmit data at 2 Mb/s with a frequency-hopping spread-spectrum system. The spec also allows fall-back operation at the 1-Mb/s speed approved by the committee last July. Products built to either speed will interoperate thanks to software in the devices that negotiates whether they communicate at 2 Mb/s or fall back to the slower rate.

In spread-spectrum systems, the transceiver sends and receives the signal over a range of frequencies--between 2.4 and 2.5 GHz in the Proxim spec--to reduce the problem of interference from electronic equipment. If there is interference at one frequency, the signal is likely to get through on another.

Frequency hopping is designed to reduce interference further by dividing the spread-spectrum band into multiple channels. As data is transmitted from one wireless transceiver to another, the signal hops from channel to channel in a specified sequence, lessening the chance of interference and improving security by making eavesdropping more difficult.

Approval of the MAC-layer protocol was a result of cooperation between (then) NCR Corp., Symbol Technologies and Xircom, Inc., all of whom had preciously submitted separate proposals. All three finally joined to create a protocol called Distributed Foundation Wireless MAC (DFWMAC).

A key point of contention was whether the protocol should be based on distributed or centrally controlled point coordination technology. The distributed design allows wireless LAN users to communicate without any links to a wired LAN. Point coordination requires devices on a wireless LAN to communicate with one another via a central point of control on a wired LAN, such as a hub.

DFWMAC support both types, allowing groups of users to create ad hoc wireless LANs for impromptu collaboration, with the ability also to link into an existing wired network through a hub or other access point.

With their higher speeds, improved security and imminent standards, wireless LANs are starting to shed their early shortcomings. Until the costs come down, however, they are more likely to become an extension to, rather than a replacement for, wired LANs, finding application where wires cannot go.

Data communications consultant Morris Edwards serves as program chairman of the Network Computing Solutions Conference and Exposition, or NetCom, which will be held in Charlotte, N.C., Oct. 12 and 13, and in Miami next March 7-9.