802.11 Wireless Info & FAQ

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RF Connector Guide

MAC Address Guide

WiFi Glossary

WiFi Security Guide





What is WiFi?

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:

WiFi Logo

802.11a
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.

802.11b
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.

802.11g
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.
802.11n
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 single-band counterparts.


What kind of range can I expect from my WiFi connection?

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.

What about extending my wireless card's range?

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 computer (RP-SMA).
  • 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.

What's the difference between Standard Polarity and Reverse Polarity?

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.
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What about securing my Wireless Network?

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 forget it).
  • 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.