Overview | Wireless LANs

Most computers in the corporate environment are tied together over wired LANs so that users can access and share data, applications, and services. However, a growing number of applications require mobility as well as network access. One way of achieving both objectives is for a notebook computer to plug into a docking station, which is wired to the LAN. Another way is for the notebook's PCMCIA card to establish a wireless connection to the nearest access point, which is wired to the LAN. Of course, desktop computers can be interconnected with each other over a wireless LAN, and connect to a wired LAN only when necessary through an access point. A network interface card (NIC) equipped with a transceiver links individual network nodes. External antennas allow for omnidirectional transmission instead of requiring a clear line of sight.

Coverage can be extended to other floors, between buildings, or across a metropolitan area using wireless bridge/routers. Since it is not necessary to install new cabling, wireless LANs offer a convenient alternative for adding or moving users. Both Ethernet and token ring LANs are supported over wireless links and the devices can be managed using standard SNMP-based management packages or vendor-specific configuration tools.

Notebook and desktop computers are not the only devices that require wireless connections. Mobile terminals—PDAs, specialized handheld terminals, and barcode scanners—connected to wireless LANs are being increasingly used to enhance business operations. Mobile data applications are raising the productivity of essential personnel and eliminating unnecessary paperwork, cutting operations costs in the process. These devices are also used to increase revenues by bringing products, services and transaction points closer to users via wireless connections.

While the use of wireless networks answers the need for mobility and solves many network administration problems, they do have their share of drawbacks. For example, wireless LANs usually transmit at slower speeds than wired LANs, and the frequencies used for data transmission are subject to interference which can impair performance. The fact that signals are radiated in the air may present security concerns. The products of many vendors are not interoperable with each other; wireless LANs are often too small to make interoperability a strong issue. And although prices are dropping, wireless LANs are still more expensive than wired LANs.

Despite these limitations, however, wireless LANs are here to stay and will continue to improve and grow. With the IEEE 802.11 standard for wireless LAN communication released in 1997, a number of basic media and configuration issues, transmission procedures, throughput requirements, and range characteristics are addressed which can help reduce the risk of product incompatibility and early obsolescence. Over the long term, the 802.11 standard is expected to help make wireless LANs price-competitive with wired networks.

One source of multivendor product incompatibility is that different wireless technologies are used to implement wireless LANs. The three popular technologies currently in use are spread spectrum, infrared, and microwave.

Spread-spectrum modulation is a more complex form of AM/FM. It uses low-power, 900-MHz radio waves. The maximum attainable speeds are 1 Mbps or 2 Mbps, which is far too slow for current 10 Mbps and 16 Mbps LANs. Infrared uses short-wavelength light for transmission and it works well at higher speeds, but it offers the least amount of coverage and requires a line-of-sight connection between devices. These problems can be easily overcome, but at the greater cost. Microwave transmission at 18 GHz is a very effective communications medium, but it requires an FCC license. This is not an obstacle, if the vendor acts on the customer's behalf to obtain the license. Although offering greater range, microwave is more expensive than either spread spectrum or infrared.