December 12, 2000, 3:02 PM — As I discussed in
href="http://www.itworld.com/Net/2629/ITW2522/">my last column,
requirements are a foundation for defining a wireless LAN's function. The next step is
to specify the technical aspects and components of a wireless LAN -- e.g. access
points, radio cards, and associated software -- that satisfy those requirements.
To ensure a successful design, execute the following steps:
Select a standard. Determine which wireless-LAN standard
best satisfies your requirements. Choose between IEEE 802.11 at 1 or 2 Mbps and href="http://mithras.itworld.com/articles/columns/net-geier-0323.html">IEEE 802.11b
at 11 Mbps. You'll soon be able to add href="http://www.itworld.com/Net/2629/ITW000829Geir/">IEEE 802.11a
products, with data rates up to 54 Mbps, to the list.
Your choice of a standard depends mostly on your data rate requirements, as I said
in my last
column. With 802.11 alternatives, you must take into account HREF="http://www.wireless-nets.com/whitepaper_spread.htm">frequency hopping vs. direct
sequence tradeoffs. Most designers now choose 802.11b because it offers
Ethernet-equivalent speeds and is priced only slightly higher than 802.11
Define optional features. Many IEEE-802.11-compliant wireless
LANs implement optional features, giving system designers more choices. For example,
designers can choose to implement 802.11's Point Coordination Function (PCF), which
delivers time-bounded data via synchronous communications using station-polling
mechanisms; in other words, it better supports real-time transmissions of video and
Another optional feature is Wired Equivalent Privacy (WEP), which provides frame
transmission privacy similar to that of wired networks by generating secret
shared-encryption keys for source and destination stations. Consider using this feature
if you need a higher security level.
Properly size the network. Be sure to determine the number of
access points necessary to provide adequate throughput, and locate them to give your
users complete coverage. Perform an RF site survey. Also, if you need higher
throughput, consider collocating access points that operate on different channels --
this increases the bandwidth available in specific areas.