802.11 Wireless Info & FAQ
|DataPro Tech Info > 802.11 Wireless Info & FAQ|
WiFi, or Wireless Fidelity, has become a popular way to
access the Internet and other network-based services. For many
companies it has become an integral part of the way they do business.
For home users, it has eased the pain of sharing broadband Internet
access at minimum cost. This document will shed light on some of the
details of WiFi that a network administrator should know and that a
wireless neophyte might find useful.
There are currently 4 main types of 802.11x wireless:
802.11a is a 54mbps standard that operates in the 5GHz range.
It uses a signal that is broadcast on more than one frequency at the
same time, making antenna design for this application a little more
complicated because you MUST have fairly broad frequency sensitivity
for it to work properly. 802.11a never really caught on due to cost.
Some wireless cards advertised today say they accept the 802.11a signal,
but almost no mainstream Access Points (AP's) are 802.11a compatible.
The APs that are 802.11a compatible are still fairly costly.
This was the wireless standard with the largest user base, as
it was the first to mix ease of setup with low cost. This standard
operates in the 2.4GHz range and offers up to 11mbps of bandwidth with a
strong signal. Offering a longer operational range than 802.11a, 802.11b's
operational range varies from 300-500 feet, depending on obstructions and
the ground plane you are working in (often the ground reflects radio
frequencies from close-to-ground antennae back at the signal source, creating
destructive interference and limiting the operational range of the
antenna). This standard is only capable of broadcasting on 1 of 11
channels at a time.
This is now the most popular version of the 802.11x series. 802.11g offers
the cost and range of 802.11b with the speed, and in some cases twice
the speed, of 802.11a. Operating in the 2.4GHz range, 802.11g often
falls just a few feet short of 802.11b on range, due to it utilizing the
upper end of the 2.4GHz spectrum, but with an allotted bandwidth of
54mbps in single-channel mode, and up to 108mbps in duplex (2-channel
broadcast) or SuperG mode, the range/bandwidth mix is making 802.11g the
wireless standard to beat. All wireless cards advertised today as
802.11g compatible are also 802.11b compatible. Some older 802.11g cards
were g-only, but these cards haven't been manufactured in a good while.
Although it is not a finished standard, many access points
and network adapters are currently implementing draft
versions of the 802.11n specification. 802.11n offers full
backwards compatibility with 802.11g/b, while providing
increased data rates of up to 150mbps for 802.11n clients.
Some of these Draft-N devices can operate in two channels for
even faster transfer rates of up to 300mbps. Most 802.11n
routers and access points can accomplish this by running in
40MHz mode, where an additional channel in the 2.4GHz
spectrum (known as the extension channel) is utilized for the
extra bandwidth. However, this method can cause interference
for 802.11g and b devices, which gives them very poor signal
quality. To address this issue, new dual-band 802.11n
routers are now available, which use the 2.4GHz band for
legacy Wireless-G and B devices, and the 5GHz band to provide
high-speed Wireless-N performance. As these dual-band access
points require additional antennas and transmission hardware,
they tend to be significantly more expensive than their
Ranges vary of course, but with an uninterrupted line of sight and
ideal conditions, 802.11b and 802.11g can both be expected to reach
about 300 feet, with 802.11b going a little further, sometimes up to 500
feet. This is assuming you are using the standard antennae that come with
most WiFi equipment. Most stock antennae are between 3 and 5dbi. Your
range will of course go up if you use a higher gain antenna.
There are several options available for extending the range of a
wireless card. The most obvious way to extend range is connecting a
larger, more powerful antenna. There are several scenarios possible
depending on what format wireless card you are working with:
- If your WiFi card is in a PCI slot:
The external antenna on your WiFi card is most likely removable,
leaving a Reverse Polarity SMA connector on the back of your
- If your WiFi card is in a PCMCIA slot:
The odds of finding an external antenna connector on the outside of your
WiFi card are quite small. Most cards sold today DO NOT have an external
connector. There are, of course exceptions, in which case your are
most likely left with an MMCX connector on the end of the card.
- If your WiFi card is plugged into a USB port:
Your most likely DO NOT have an external antenna connector. If you want
to extend the range of your WiFi antenna you will need a USB extension cable.
- If your WiFi card is built in (Intel Centrino or equivalent):
Again, you most likely DO NOT have an external antenna connector. If
you have reception problems, you will have to find another way around
the problem, like using a PCMCIA or USB WiFi card.
Beyond determining what kind of connector you have on your WiFi card,
you must also determine the type of connector on your antenna. For more help, see our guide to the most common RF and Wireless connectors.
The difference is simple but important. If you use the Standard
Polarity connectors as a base-line, the Reverse Polarity connectors'
genders are reversed. In a standard polarity SMA connector, the male
has a pin and the female has the receptacle for said pin. In the Reverse
Polarity connector, the male side has the pin receptacle and the female
side has the pin. Generally we consider the Male side to be the connector
which has the mating collar.
Important things to remember about antennae:
- Make sure that if you purchase a more powerful antennae that it is
the same polarization as all the other antennae you are using. There are
many types of antennae on the market, and some are vertically polarized
while others are horizontally polarized. There are even a few that are
circularly polarized, though they are not very common. To get the
most out of your antennae you need to pick an antennae topology and stick
with it. If you buy an access point with a vertically polarized antenna
and you want to use a larger antenna on a computer to connect to it, you
should purchase another vertically polarized antenna. When you mix the
topologies, the signal-to-noise ratio (snr) goes up drastically, making
for a weaker and less reliable connection.
- The FCC limits the amount of radio noise an antennae can emit, so
if you're designing/building your own antennae, be sure it fits within
the guidelines set forth by the FCC in Title 47.
- Try to keep the length of cable between the antenna and computer or
access point to a minimum. Depending on the type of wire used, you lose
a certain amount of signal strength over a given distance. The heavier
the shielding used on the cable the less signal is lost per meter, but
even with the best shielded wire available you have to account for signal
loss over the antenna cable when picking a location for the antenna.
There are several ways to secure your network from any passersby
who might try to gain quick access. It should be known, however, that
if someone really wants access to your WiFi network, they will get access,
just like a wired network.
- Change the SSID of your access point. Not doing so automatically makes
you a target.
- Change the administrator password for your access point (and don't
- Enable encryption, at least WEP, WPA if your hardware supports it.
WEP is as old as commercial 802.11b and can be cracked, but it provides
more protection than not turning on encryption. WPA is far more secure,
but older hardware does not support it.
- Generate your encryption keys manually and randomly.
Taking security to the next level (higher difficulty, both enabling and defeating):
- Use MAC Address filtering. Every ethernet card, wireless or not,
has a unique identifier MAC Address. By filtering out all but a few
specified address, you can limit who is allowed to received airtime
to your AP. Of course, your wireless signal is still flying through
the air and can therefore be intercepted, but more security never hurts.
- Use static IP's in a manually specified range. While not fool-
proof, it keeps any would-be intruders guessing about how to connect
to your AP.
The steps involved in many of these security options differ from
manufacturer to manfacturer, so check your access point documentation
or refer to the manufacturer's web page.
For more information on securing a WiFi network, see the WIFi Security Guide.
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Written by Flynn Martin
for DataPro International Inc.|
Unauthorized duplication strictly prohibited.