A wireless LAN can be an extension of a fixed, wired LAN, or can exist as a peer-to-peer network. As wireless clients, a notebook computer uses a PC Card and a desktop uses a PCI card that receives and transmits a radio signal, converting it into digital data.
Wireless clients connect to the wired LAN via an access point, the generic name for a wireless hub. An access point acts just like the base station of a cordless phone, plugging directly into the wired network. A PC can also act as an access point by using access point software.
Each access point has a certain range - if you roam outside that range with your trusty notebook, another access point will pick you up, without any disruption to your network connection. It is exactly the same principle as your mobile phone passing its connection to different "cells" as you drive from suburb to suburb (which is why the Yanks call their mobiles "cellular phones").
The new 802.11 HR standard provides a top communications speed of 11Mbps, which puts it on par with standard Ethernet performance. Like Ethernet, wireless LAN is a shared technology, so the more people attached via the same access point, the less bandwidth is available.
A single access point supports multiple users, the optimum number dictated by their distance from the access point and their bandwidth requirements. 3Com's AirConnect Access Point will support a maximum of 63 users. Compaq says its WL400 Hardware Access Point can handle 150 "nominal users", who are mostly idle and check an occasional text e-mail; 100 "mainstream users", who use a lot of e-mail and transfer medium-sized files; and 50 "power users", who are constantly on the network and deal with large files.
Data rates fall as you get further from the access point. 3Com's AirConnect unit has a range of approximately 100m in a "standard office environment", and will step down through 5.5, 2 and 1Mbps as distance from the access point (and the number of users) increases.
Once the number of users exceeds the maximum for a single access point, you simply add another one and switch it to a different operating channel (frequency).