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Intel(R) PRO/Wireless LAN adapter support a variety of network
configurations, including 802.11b and 802.11a wireless LANs in both ad hoc and
infrastructure modes. The following guidelines address the specific features of
each type that must be taken into consideration when planning for installation
of a wireless LAN.
The bullet items below provide an overview of the differences between the two
types of wireless LAN. It is important to understand the strengths and weaknesses of each, in order to maximize overall system performance.
With correct installation and implementation, both types of WLAN offer good
performance. If speed and interference are not major considerations (for
example, in a large open warehouse), 802.11b would be adequate. In a small
office in a building with many other types of microwave devices, 802.11a would
be a better choice. On-site testing via the site survey process is the best way
to get accurate information on which type of network to use, or on how to create
a network in a dual-mode 802.11b and 802.11a environment.
When designing and setting up an 802.11a and an 802.11b wireless LAN in the same location, using Intel(R) PRO/Wireless 5000 Dual Access Points, keep the following considerations in mind:
Consider the degree to which the wireless LAN will interact with the
conventional wired LAN. Some legacy systems, such as older mainframe networks,
may not support WLANs without additional hardware or software.
The size of the site determines what equipment you will need and where to place it.
These parameters will be different for 802.11b and for 802.11a networks.
See Which Type of Wireless Network for guidelines.
The shape of the site is also a concern. Radio frequency (RF) transmissions propagate
differently in a narrow space, such as a hallway, than in a large open area,
such as an office filled with cubicles. Open doorways might also affect RF
propagation.
The right kind of power supply should be available for access points. The
following are electrical installation alternatives listed in order of most to
least desirable.
Configurations without a UPS are not recommended. A dedicated circuit is
preferable to a non-dedicated circuit. Non-dedicated circuits have open
receptacles; the load and type of use cannot be predicted at the time of
installation. Although the current draw of the access points is minimal, other
devices on the circuit can affect the access points.
If it is absolutely necessary to have a non-dedicated circuit, it is
recommended that the circuit not support the following:
In all cases, the power to the access points must be unswitched and available 24
hours per day. It is recommended that the power never be provided from an energy
management system.
Physical and environmental conditions affect the performance of wireless LAN
equipment. Wireless LAN sites should not be excessively hot, cold, humid, or
dusty. The area should also be relatively free of electronic equipment that
generates background Radio Frequency (RF) noise, which can interfere with
wireless LANs.
For optimal performance, do not locate access points near transformers,
heavy-duty motors, fluorescent lights, microwave ovens, refrigerators, and other
industrial equipment. See the site survey section for environment
recommendations.
Signal loss can occur when metal, concrete, walls, or floors block
transmission. Locate access points in open areas or add access points as needed
to improve performance.
For simplicity, we talk of "moving around," but signals will
also travel up and down. This can be good or bad, depending on your
situation.
The good news is that, in a multistory building, you can usually
communicate between floors using one access point. As usual, the
actual range depends on the floor material, which can only be
checked with a site survey. Expect some dead spots directly over (or
under) large metal air conditioning ducts, and similar metal surfaces.
The bad news is that another company on the floor above or below
you may innocently install its own system, and, for example, place an
access point directly below your desk. A bit of diplomatic mutual
planning helps both systems to operate at maximum efficiency. The
placement of access points, and the choice of channels, needs to be worked out between users.
Some elevators are transparent to microwaves, and others act as a
closed metal box. In the latter case, if network operation in the
elevator is required, you may have to install an access point in the
elevator. This requirement should be incorporated into your site survey.
Some of the equipment and materials that can interfere with wireless LAN
transmissions include:
Obstruction Degree of Attenuation Example Open Space Cafeteria, courtyard Wood Inner wall, office partition, door, floor Plaster Inner wall (old plaster lower than new plaster) Synthetic Materials Office partition Cinder block Inner wall, outer wall Asbestos Ceiling Glass Non-tinted window Wire Mesh in Glass Door, partition Metal Tinted Glass Tinted window Human Body Large group of people Water Damp wood, aquarium, organic inventory Bricks Inner wall, outer wall, floor Marble Inner wall, outer wall, floor Ceramic (Metal Content or Backing) Ceramic tile, ceiling, floor Paper Roll or stack of paper stock Concrete Floor, outer wall, support pillar Bulletproof Glass Security booth Silvering Mirror Metal Desk, office partition, reinforced concrete, elevator shaft, filing
cabinet, sprinkler system, ventilator The key to successful setup and installation of your
wireless LAN is the site survey. The main tools of the site survey are:
The survey procedure is simple: Move around your area and plot the strength of
your signal at various locations. Repeat the process for each intended access
point location. As you move around, you will probably encounter some problems. Major area problems are usually associated with your "transmitter" location. If you placed the transmitter on a wall
containing a metal air conditioning duct or similar metal surface, you will have a serious
problem with range, and a very large dead spot. Move the transmitting unit and repeat the
tests.
Localized problems can be due to some hidden building characteristic. If you
draw connecting "equal strength" signal level lines on your map, it will help you visualize problem areas, and may
hint towards the best method of addressing them. These tests will show you where to mount your access
points, and how many you will need to get good building coverage.
Seamless coverage means that you can move around the entire coverage area, and always
stay connected. This requires software that can detect the fact that your signal is dropping down at one access point, and
going up at another, thus triggering a seamless handoff between them. Keep in mind that this
process will not work unless there is a
reasonable signal level overlap of the signals in the two areas. If you lay out your system without this signal overlap, the user will experience an annoying signal dropout as he moves around.
Done with your building survey? Now go outside your facility, and repeat the
above measuring process. Check how far down the street your signal goes. You can move your transmitter to increase or decrease this range as
appropriate.
For detailed information about conducting a site survey, see the Site Survey section of this guide. For
instructions on how to use site survey software, see Using the Site Survey Tool.
Copyright (c) 2003 Intel Corporation.
Researching the Site
Which Type of Wireless LAN?
802.11b and 802.11a Compared - What to Expect
Note: A site survey done for
an existing 802.11b network installation will
not work for an 802.11a network that replaces the 802.11b network or is added to
a site with an existing 802.11b network. A new site survey should be done and a
new coverage area floor plan should be created.
Guidelines for Networks Using Dual 802.11a/802.11b Access Points
Interaction with Wired Networks
Size and Shape of the Site
Electrical Power
Environmental Interference
The Vertical Dimension
Elevators
Interference from Equipment and Materials
None
Low
Low
Low
Low
Low
Low
Medium
Medium
Medium
Medium
Medium
Medium
High
High
High
High
Very High
Very High
Site Survey Overview
The Site Survey Procedure