Next, let's consider bandwidth. If you have 100 PCs sharing one server with a 100M bit/sec. interface, you might say that each PC needs 1M bit/sec. Even an 802.11b WLAN can provide 1M bit/sec. to one station, but of course not to 100 stations at the same time. But all 100 PCs are probably not accessing the server at once. You really need to define your requirements for number of simultaneous users and per-user throughput. For example, suppose you decide that any single user requires 2M bit/sec. with 25 users needing simultaneous access at any time. That's an aggregate throughput of 50M bit/sec.
Now, how do you know whether your 802.11a WLAN can support this? Standard 802.11a data rates range from 6 to 54M bit/sec. But data rate varies with distance, so again the answer depends upon your actual WLAN layout. How far your stations are from your APs will directly impact throughput, and effective application throughput is about half the data rate. Conduct a site survey to determine the effective throughput delivered to each station, laying out APs so that every station receives the per-user throughput that you require. Finally, consider number of users per AP - stations using the same channel share the aggregate bandwidth provided by that channel.
This was first published in January 2003