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Wireless LAN Overview: Intel(R) PRO/Wireless 2200BG User's
Guide
About Wireless LAN Technology
A wireless network connects computers
without using network cables. Computers use radio
communications to send data between each other. You can
communicate directly with other wireless computers, or connect
to an existing network through a wireless access point. When
you set up your wireless adapter, you select the operating mode
for the kind of wireless network you want. You can use your
wireless adapter to connect to other similar wireless devices
that comply with the 802.11 standard for wireless
networking.
Choosing a Wireless LAN
Wireless LANs can operate with or without access points,
depending on the number of users in the network. Infrastructure
mode uses access points to allow wireless computers to send and
receive information. Wireless computers transmit to the access
point, the access point receives the information and
rebroadcasts it to other computers. The access point can also
connect to a wired network or to the Internet. Multiple access
points can work together to provide coverage over a wide
area.
Peer-to-Peer mode, also called Ad Hoc mode, works without
access points and allows wireless computers to send information
directly to other wireless computers. Ad Hoc Mode is only
supported in 802.11b and 802.11g networks. You can use
Peer-to-Peer mode to network computers in a home or small
office or to set up a temporary wireless network for a
meeting.
Configuring a Wireless LAN
There are three basic components that must be configured for
an 802.11 wireless LAN to operate properly:
- Network Name: Each wireless network uses
a unique Network Name to identify the network. This name is
called the Service Set Identifier (SSID). When you set up
your wireless adapter, you specify the SSID. If you want to
connect to an existing network, you must use the name for
that network. If you are setting up your own network you
can make up your own name and use it on each computer. The
name can be up to 32 characters long and contain letters
and numbers.
- Profiles: When you set up your computer to
access a wireless network, the wireless client manager
creates a profile for the wireless settings that you
specify. If you want to connect to another network, you can
scan for existing networks and make a temporary connection,
or create a new profile for that network. After you create
profiles, your computer will automatically connect when you
change locations.
-
Security: The 802.11 wireless networks use
encryption to help protect your data. Wired equivalent
privacy (WEP) uses a 64-bit or 128-bit shared
encryption key to scramble data. Before a computer
transmits data, it scrambles the data using the secret
encryption key. The receiving computer uses this same
key to unscramble the data. If you are connecting to an
existing network, use the encryption key provided by
the administrator of the wireless network. If you are
setting up your own network you can make up your own
key and use it on each computer.
- Wi-Fi Protected Access (WPA) is a
security enhancement that strongly increases the
level of data protection and access control to a
WLAN. WPA mode enforces 802.1x authentication and
key-exchange to strengthen data encryption. WPA
utilizes its Temporal Key Integrity Protocol
(TKIP). TKIP provides
important data encryption enhancements that include
a per-packet key mixing function, a message
integrity check (MIC) named "Michael", an extended
initialization vector (IV) with sequencing rules,
and a also re-keying mechanism. Using these
improvement enhancements, TKIP protects against
WEP's known weaknesses.
- Cisco Client Extention (CCX) is a server
and client 802.1x authentication via a
user-supplied logon password. When a wireless
access point communicates with a Cisco LEAP-enabled
RADIUS (Cisco Secure Access Control Server (ACS)
server), Cisco LEAP provides access control through
mutual authentication between client wireless
adapters and the wireless network and provides
dynamic, individual user encryption keys to help
protect the privacy of transmitted data.
Identifying a Wireless Network
Depending on the size and components of a wireless LAN,
there are many ways to identify a wireless LAN:
- The Network Name or Service Set Identifier
(SSID): Identifies a wireless network. All wireless
devices on the network must use the same SSID.
- Extended Service Set Identifier (ESSID): A
special case of SSID used to identify a wireless network
that includes access points.
- Independent Basic Service Set Identifier
(IBSSID): A special case of SSID used to identify a
network of wireless computers configured to communicate
directly with one another without using an access
point.
- Basic Service Set Identifier (BSSID): A unique
identifier for each wireless device. The BSSID is the
Ethernet MAC address of the device.
- Broadcast SSID: An access point can respond to
computers sending probe packets with the broadcast SSID. If
this feature is enabled on the access point, any wireless
user can associate with the access point by using a blank
(null) SSID.
Surveying the Site of Your Wireless
LAN
Conducting a site survey for your
wireless LAN is the most crucial step in the process of setting
up a wireless network. It greatly reduces the amount of
troubleshooting you will have to do once you have the wireless
LAN set up and ready for connection testing. To conduct a site
survey, you will need the following tools:
- An access point (or laptop computer) that is set up to
be the transmitter. It should be mounted near and at the
same height as the designated location of your wireless
LAN.
- A laptop that will act as the mobile receiver. It must
contain your site survey software.
- An area or building map, which will be used to plot the
strength of your signals.
Once you have the tools you need, you are ready to survey
the inside of the building. Launch the site survey software on
the mobile receiver laptop and carry it around in the intended
wireless LAN area to test the signal strength. Be sure to also
check the signal strength of each intended access point
location. If you encounter problems while surveying the site,
make sure your transmitter laptop is not located on a wall
containing metal, such as an air-conditioning duct, which will
interfere with the range of your signal. Simply move the
transmitter and test the signal strength again. For users to
have seamless coverage when moving from access point to access
point, the signal levels at each point must overlap. There is
software available that will seamlessly hand off changing
signal levels from one access point to another.
Your building's infrastructure can sometimes interfere with
the microwave signal, but finding the location and cause of the
interference will allow you to figure out the best place to
mount your access points for optimal area coverage. Microwave
signals travel in all directions, which means there is one
access point for a multi-floor building. However, the range is
highly dependent on the material used to construct the
flooring, especially metal materials. Once your signal strength
is strong inside the building, you are ready to check the
strength outside the building. To do so, simply carry the
mobile receiver laptop as far down the street or around the
building as you can go without losing significant signal
strength. If possible, you should be aware of the types of
networks being used by the companies on the floors above and
below you, so that you can work together in harmony. With
wireless networks, security is very important and if you
communicate with those around you, you are better prepared to
select the right channels, as well as the best location for
access points.
Factors Affecting Range
Although access points can transmit signals up to 60 feet
away in an area with many walled barriers or as much as 500
feet away in a large open area, the range is affected by
the following factors:
- Building materials, such as steel and drywall, can
shorten the range of the radio signals.
- Physical layout of the area can interfere with the
signals and cause them to be dropped.
- Electronic noise from cell phones, microwave ovens, or
other devices on the same frequency can interfere with the
transmission of the signals.
- Range is inversely proportional to data rate, so the
faster that the signals are sent, the less distance they
will travel.
Taking these factors into consideration when you survey the
site for your WLAN is key to providing all of your users with
undisturbed mobile connectivity. Using multiple access points
will, of course, reduce the impact of these factors if your
area has dividing walls throughout.
What is a Site Survey?
A site survey is an in-depth examination and analysis of a
proposed wireless LAN site. The purpose of a site survey is to
determine the number of access points needed, the types of
antennas needed, and the best placement for those access points
and antennas. Although the goal of a site survey is simple, the
means of arriving at that goal are not. Some of the steps
involve taking measurements, but most involve experience,
trial and error, and a little guesswork rather than numbers and
figures. When to Perform a Site Survey Intel® recommends
that you perform a site survey prior to installing a wireless
LAN. Site surveys are especially important when:
- You are installing a new site: Evaluate the
placement of the access points and antennas throughout the
proposed site.
- You are changing an existing site: When
modifying or extending an existing network structure,
re-evaluate the placement of the access points and
antennas. If you need a different level of coverage in some
areas, you may need to move, replace, or supplement access
points and antennas.
- You are physically changing the site: Remodeling
may introduce new sources of interference, such as motors
and metal structures within the coverage area of the access
point, even if it does not directly effect the sites where
the access points are located.
Elements of an Effective Site Survey
An effective site survey requires four elements. Failure to
commit the appropriate time, money, and energy to accomplish a
proper site survey in advance may result in greater
expenditures of money and time later, when problems arise that
require repeated adjustments to the wireless configuration. The
three elements of an effective site survey are:
- Examine the network usage problems solved by the
wireless LAN.
How many clients need a wireless LAN connection? What
areas of the site require wireless LAN connectivity? How
many hours each day is wireless LAN connectivity required?
Which locations are likely to generate the largest amount
of data traffic? Where is future network expansion most
likely?
- Study blueprints of the proposed wireless LAN
site.
A site blueprint provides a map of the site as well as the
location of objects, such as walls, partitions, and
anything else that could affect the performance of a
wireless LAN. Examining the site blueprint prior to
conducting the physical walk-through helps you identify
areas in which wireless equipment is likely to perform well
and areas where it is not. Many obstructions are not
readily visible and, in some cases, a room originally built
for a specific purpose, such as a radiology lab, might have
been converted into something completely different, such as
a conference room. The blueprint may also show areas
proposed for future building expansion. To prepare for the
next step of the site survey, mark possible wireless device
locations on the blueprint and refer to the marked
blueprint during the physical walk-through and
inventory.
- Conduct a physical walk-through and
inventory.
The primary purpose of the physical walk-through is to
document any items or materials near a proposed device
location that may interfere with reception or transmission
and affect network performance. Document stock and
inventory levels, current environmental conditions and any
materials that may interfere with the wireless LAN.
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