How It Works: Wireless Networking
- Share resources and move files without wires.
- Ease of setup and reliability make it suitable for office or home use.
- Products from different manufacturers often incompatible.
- Much more expensive than wired networking technologies like Ethernet.
If you need to connect two or more computers where it's impractical or difficult to use standard networking cables, a wireless network might suit your needs. Each PC in a wireless network is equipped with a radio transceiver, often called a wireless LAN adapter or card, that sends and receives radio signals to and from other PCs on the network. You'll find adapters in various internal and external configurations, for both desktop PCs and notebooks.
Similar to a wired Ethernet network, a wireless LAN sends data in packets. Each adapter has a permanent, unique ID number that serves as an address, and each packet contains the data as well as the address of the recipient and that of sender. Similar to an Ethernet adapter (see "How It Works: Ethernet"), a wireless LAN card checks for an opening before sending a packet out to the network. When it detects a pause, it sends the packet. If it senses other data on the radio frequency, it waits for a moment and then checks again.
Wireless LANs commonly use one of two topologies, or ways to organize the network: In an ad-hoc topology--also called a peer-to-peer network--each PC equipped with a wireless adapter broadcasts and receives data to and from all other transceiver-equipped PCs within about 300 feet. In an infrastructure topology, each PC sends data to and receives data from an access point, which is mounted on a wall or ceiling and usually looks like a small box with an extended antenna. When the access point receives data, it can resend the signal (with greater range) over radio frequencies to PCs in its coverage area, or it can transfer the data to a wired Ethernet network. Access points in an infrastructure network offer greater range, but the extra equipment costs more.
All the standards call for adapters to use a small segment of the 2.4-GHz radio band, leaving them with little radio bandwidth for sending data. But adapters use one of two signaling protocols to increase efficiency and security: Frequency hopping spread spectrum rapidly sends part of each data packet across several adjacent radio frequencies, one right after the other, until the entire message has been sent. The speed at which these hopping signals change frequency provides a measure of security, because most radios can't follow them. The direct sequence spread spectrum method divides the radio band into three equal parts and spreads the entire packet across one of those sections. Direct sequence adapters encrypt and decrypt data, so unintended recipients using a radio to pick up the signal would hear only white noise.
Wireless LAN vendors usually state the maximum transfer rate of their adapters. Models that adhere to the 802.11 standard transfer data at 2 megabits per second, using either the frequency hopping or direct sequence method. Adapters that use the OpenAir standard transfer data at 1.6 mbps using frequency hopping. And a new standard, HomeRF, can send both voice and data (using frequency hopping) at 1.6 mbps. The fastest wireless LANs use the IEEE 802.11b High-Rate standard, also called WiFi, to move data at a maximum speed of about 11 mbps using the direct sequence protocol.
Invisible Wires: Network of the Future?
Wireless LANs hold a certain futuristic, roam-anywhere appeal, but cost and performance issues have kept them from making inroads to offices or homes. The overwhelming majority of office networks use Ethernet, due to its established, relatively inexpensive infrastructure. In the home, most users opt for phone-line networking, which uses existing phone lines to connect multiple PCs and allow shared Internet access.
Wireless LANs used to cost so much more than their wired counterparts that few even considered them. Prior to 1999, adapters cost at least $500, compared to about $20 for a 10Base-T Ethernet card or about $100 for a phone-line hook-up. All that changed when Apple introduced its AirPort wireless networking system for the Macintosh, which offers 11-mbps throughput for $99 per node. Since then, several vendors have introduced adapters that make wireless LANs a more attractive option for both home and small-business PC users. Market research firm Yankee Group predicts that wireless LANs will make up a quarter of home networks by 2003.
Today, you can find wireless adapters that connect in every way to PCs: internal PCI and ISA cards, external Universal Serial Bus models, and PC Cards or CardBus cards for notebooks. Home- and small-office versions from companies like Proxim and WebGearcost from $70 to $130 per adapter. These prices hold true regardless of which standard the adapters use. Industrial-strength cards suitable for large networks cost between $500 and $700 but offer features like roaming (the ability to use any access point on the network).
Users can add access points to extend the range of their network or help manage the flow of traffic. Access points, including those from Apple (which only work with Macintosh computers), Lucent, and Proxim, run between $300 and $700. Access points can also serve as bridges to wired networks.
Among the four standards competing for supremacy in the wireless LAN market--802.11, 802.11b, OpenAir, and HomeRF--analysts predict 802.11b will become dominant. With transfer speeds of 11 mbps, 802.11b moves data four times as fast as any of the others but doesn't cost more. However, OpenAir and HomeRF, which broadcast with the frequency hopping method, could soon be moving as fast as WiFi: FCC restrictions have so far kept frequency hopping speeds to 2 mbps or slower, but OpenAir and HomeRF industry groups are lobbying to raise the limit to 11 mbps.
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