Wireless LAN Technology
The last common LAN technology is wireless, using infrared light or radio waves instead of wires or fiber optics to transport the network signals. You'll be limited to data rates in the 111Mbps range, but without wires, you'll find it easier to accommodate mobile users and to put computers where wires are difficult to place.
After years of proprietary systems, wireless networks are converging to follow the IEEE 802.11 standard, which specifies half-duplex network operation using the same CSMA/CD technique that we described for Ethernet LANs.
There are several options in the IEEE 802.11 standard, so you'll have to be careful when buying hardware to ensure that what you buy all uses the same option (see Table 1).
Wireless 802.11 Network Options
1, 2, 5.5, and 11Mbps
1 and 2Mbps
The Modulation column in Table 1 refers to the mechanism used to convert data from your computer to signals capable of wireless transmission. Both frequency hopping and direct sequence are types of spread spectrum modulation, a technique for spreading a signal over a wide frequency range both to permit multiple transmitters to operate at the same time and to help improve the system's noise resistance.
Even though frequency hopping and direct sequence modulation both use radio technology, the two modulations are absolutely incompatible. You won't be able to receive a frequency-hopped signal with a direct sequence network adapter, and vice versa.
Faster wireless network adapters should be capable of interoperating with slower ones using the same modulation. Check with the manufacturer to be sure.
You'll find two topologies in IEEE 802.11 wireless networks: ad hoc connections and star-connected configurations using an access point (see Figure 1). The ad hoc organization works well for all-wireless setups (and costs less); the access point organization is better when you want to use the wireless network as an extension of a wired LAN.
Wireless network topologies
Some wireless LAN vendors also offer a third topology in which two stations operate in a point-to-point mode using directional antennas. You use point-to-point stations as a wireless bridge between two wired LANs when you can't run a wired connection.