Everything you need to know about implementing a wireless LAN
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.
Define the wired backbone. If your wireless LAN's users need to
communicate with users at other access points, you need to specify a wired backbone,
such as Ethernet or Token Ring, to provide physical interconnections between access
points. If you have a wired LAN, you can connect the access points to open ports on
your switch or hub.
Define href="http://www.itworld.com/AppDev/1376/ITW2159/"> application
connectivity software. These are the tools for interfacing devices that
operate on the wireless LAN with host systems. For instance, if you need to reach
applications that run on an AS/400 or Unix box, you'll probably need to specify
terminal emulation software for your handheld devices. Consider using wireless
middleware if high reliability -- or the ability to interface with data located on
multiple, dissimilar host systems -- is required.
Choose products. Consider the products' technical
specifications, such as standards compliance, optional features beyond the scope of the
802.11 standard, price, warranties, and technical support capability.
Verify the design. This includes verifying that the
technologies, configurations, and product selections truly satisfy your requirements.
To do this, you can run simulations and set up a physical prototype.
A simulation uses software models, like HREF="http://www.opnet.com/products/library/WLAN.htm">Opnet, that artificially
represent an 802.11 network's hardware, software, traffic flows, and utilization. You
can run simulations and check results quickly; days of network activity go by in
minutes of simulation runtime. Simulation tools, however, are generally costly, with
prices in the tens of thousands of dollars. You might be better off hiring a company
that already owns a simulation tool.
Run a physical prototype by constructing and testing part of the system you wish to
verify. You get real results because you're using the actual hardware and software. Be
prepared to reconfigure your prototype as you go. Don't skip this step if you need to
ensure compatibility among 802.11-compliant products from different vendors.
Document the design. As with requirements and other phases of a
system implementation project, you should document the details of the design before you
implement it. Be certain to document schematics, building-layout drawings, and bills of
materials or parts lists.
Once you finish these steps, you'll be ready to procure the components.