Introduction to Wireless LAN Analysis
The goal here is to determine whether the wireless system will operate
adequately before your client spends lots of money on hardware and
installation of the system. This pre-installation analysis significantly
reduces risk for complex implementations.
For example, the deployment of a wireless LAN to support 3,000 users
in a stock exchange facility would entail simulation or careful analysis
of a working prototype before investing money to purchase the
necessary hardware. Practical utilization models for this level of
overall utilization do not exist for wireless LANs. Some analysis and
simulation, however, will help verify that there is a quantity and
placement of access points that will actually satisfy requirements. In
such cases, it is common to use a protocol analyzer and a device
capable of emulating many clients and traffic types.
RF Site Surveys
One of the first steps of deploying a wireless LAN where you will
probably utilize analysis is when performing a RF site survey. The site
survey is done prior to installing the wireless LAN because the site
survey discovers potential sources of interference and identifies the
optimum installation location for access points. The measurements of
RF signals and proper interpretation of signal quality and throughput
tests, that is part of “analysis” as a whole, is critical for properly
defining and qualifying range boundaries.
Some installers of access points simply use the data rate at which the
client is associated with an access point as the basis for the range
boundary. For example, an installer may interpret that the range
boundary has been reached when the data rate on a laptop with
association with an 802.11g access point drops to 24 Mbps. The
problem with this approach, however, is this data rate is merely the data
rate that the 802.11 data frames are sent. Access delays, collisions with
nearby stations, and errors due to interference may prompt significantly
high transmission retry rates. These events in turn lower actual
throughput dramatically. For example, a user next to a microwave
oven cooking popcorn and trying to browse the web will experience
significant page load delays, even though the associated data rate is 54
Mbps.
