Introduction to Wireless Technology

Transmitting a signal using the typical 802.11 specifications works a lot like it does with a basic Ethernet hub: They’re both two-way forms of communication, and they both use the same frequency to both transmit and receive, often referred to as half-duplex and mentioned earlier in the chapter.

Wireless LANs (WLANs) use radio frequencies (RFs) that are radiated into the air from an antenna that creates radio waves. These waves can be absorbed, refracted,or reflected by walls, water, and metal surfaces, resulting in low signal strength. So because of this innate vulnerability to surrounding environmental factors, it’s pretty apparent that wireless will never offer us the same robustness as a wired network can, but that still doesn’t mean we’re not going to run wireless. Believe me, we definitely will!

We can increase the transmitting power and gain a greater transmitting distance, but doing so can create some nasty distortion, so it has to be done carefully. By using higher frequencies, we can attain higher data rates, but this is, unfortunately, at the cost of decreased transmitting distances.

And if we use lower frequencies, we get to transmit greater distances but at lower data rates. This should make it pretty clear to you that understanding all the various types of WLANs you can implement is imperative to creating the LAN solution that best meets the specific requirements of the unique situation you’re dealing with.

Also important to note is the fact that the 802.11 specifications were developed so that there would be no licensing required in most countries—to ensure the user the freedom to install and operate without any licensing or operating fees. This means that any manufacturer can create products and sell them at a local computer store or wherever. It also means that all our computers should be able to communicate wirelessly without configuring much, if anything at all.

Various agencies have been around for a very long time to help govern the use of wireless devices, frequencies, standards, and how the frequency spectrums are used. Table 1 shows the current agencies that help create, maintain, and even enforce wireless standards worldwide.

Table 1:Wireless Agencies and Standards

Because WLANs transmit over radio frequencies, they’re regulated by the same types of laws used to govern things like AM/FM radios. It’s the Federal Communications Commission (FCC) that regulates the use of wireless LAN devices, and the Institute of Electrical and Electronics Engineers (IEEE) takes it from there and creates standards based on what frequencies the FCC releases for public use.

The FCC has released three unlicensed bands for public use: 900MHz, 2.4GHz, and 5.7GHz. The 900MHz and 2.4GHz bands are referred to as the Industrial, Scientific, and Medical (ISM) bands, and the 5-GHz band is known as the Unlicensed National Information Infrastructure (UNII) band. Figure 1 shows where the unlicensed bands sit within the RF spectrum.

Figure 1:Unlicensed frequencies

So it follows that if you opt to deploy wireless in a range outside of the three public bands shown in Figure 1, you need to get a specific license from the FCC to do so. Once the FCC opened the three frequency ranges for public use, many manufacturers were able to start offering myriad products that flooded the market, with 802.11b/g being the most widely used wireless network found today.

The Wi-Fi Alliance grants certification for interoperability among 802.11 products offered by various vendors. This certification provides a sort of comfort zone for the users purchasing the many types of products, although in my personal experience, it’s just a whole lot easier if you buy all your access points from the same manufacturer!

In the current U.S. wireless LAN market, there are several accepted operational standards and drafts created and maintained by the Institute of Electrical and Electronics Engineers (IEEE). Let’s take a look at these standards and then talk about how the most commonly used standards work.