Chapter 1: Getting Wise to Wireless LANs

In This Chapter

Checking out wireless technologies and standards

Getting the skinny on frequencies and modulation techniques

Comparing the different solutions on the 802.11 networking technologies

Wireless technologies have been around for over a hundred years, with Nikola Tesla and Guglielmo Marconi making commercial use of wireless technologies from the beginning of the 20th century. With each major improvement in technology through the 20th century, there was an improvement in wireless communications. Just as people used early wireless to transmit traditional telegraph signals, people today use wireless to transmit traditional networking signals.

But mobile technology has gone way beyond the brick-like phones of the 1980s and has invaded all aspects of society. It would be rare for a networking specialist today to not have to work with wireless devices or wireless networking. This chapter reviews where this technology stands today and where it has come from and gives you a good overview of wireless technologies in general, as well as the specifics for wireless LAN technologies that you will likely encounter on the market. You look at the standards, basic types of wireless networking in use, the types of modulation used with WLANs, and the types of WLANs that are available for you in the 802.11 range.

As you progress through the rest of Book V, you see the basics of how to lay out your network (in Chapter 2), secure your network (in Chapter 3), and finish in Chapter 4 with an overview of the wireless solutions currently available from Cisco.

Understanding the Benefit of Wireless LANs

The main goal of wireless networking is to provide mobility to network users, regardless of where they and their network access devices may be. Within an office, this goal may be that moving users from one office to another should be easier, which with wired networking might require that you pay for the costly and manual job of running cables through the ceilings and walls. Outside of your office, wireless networks give you access to the Internet or even to corporate resources on an as-needed, where-needed basis.

A wide variety of networking devices exists in the world today, from smartphones to netbooks to media players. People have developed a reliance on getting data directly from the Internet using high-speed connections. Because users have all sorts of wireless gadgets, they do not want to download and store information, but rather grab it from where it is and use it where they are. As a result, users have an ever-increasing desire to be able to access this information in more and more locations, wherever they may be.

Learning the Wireless Technologies

When wireless networks first emerged onto the market, the technologies were good only for limited distances. As the technologies have improved, so has the range of their usability. Four main classes of wireless networks exist based on range and geographical areas:

• Wireless personal-area network (WPAN): The WPAN makes use of short-range wireless technologies, usually less than 10 meters, or 11 yards. These technologies include IrDA, Bluetooth, and ZigBee. Bluetooth has replaced IrDA as the main WPAN technology in use today, and ZigBee is an up-and-comer in that arena. Personal-area networks join devices such as cellphones to computers to sync data and wireless earpieces to phones.

• Wireless local area network (WLAN): WLANs make use of LAN technologies and cover a larger area than that of the WPAN. A WLAN typically provides network connectivity throughout an office, a building, or several buildings within a small geographical area, with all the networking components connected via LAN technologies. The technology used for a WLAN is short range and typically includes, but is not limited to, 802.11 networking components.

• Wireless metropolitan-area network (WMAN): With another increase in the geographical area, you deal with the WMAN. The technologies used in a WMAN allow wireless connections over longer ranges than the WLAN, which are limited to several hundred meters or yards. The WMAN uses technologies such as WiMAX, which can cover several kilometers or miles. The distinction between the WLAN and WMAN is made primarily by the types of technology used.

• Wireless wide-area network (WWAN): The largest area covered is the WWAN, which uses public carriers rather than private equipment. The public carriers may make use of WiMAX but most often make use of other cellular network technologies (such as GPRS, HSDPA, and 3G) to communicate. When using a device on a WWAN, the user can connect to his office network via a secured connection or connect two offices within the area of the cellular network provider.

Following the Standards

When you move into a new neighborhood, sometimes you have good neighbors who respect your property boundaries, while other times, your neighbors encroach on your property and are a general nuisance; the same is true when your property is your wireless network. When working with wireless networks, your neighbors may interfere with your network by generating traffic on the same frequencies you are using, or by using devices that encroach on the frequencies that you are using. This issue is especially true when using unlicensed radio frequency (RF) bands, but it is easier to deal with when using the limited licensed radio bands. All commercial wireless networking solutions operate in the unlicensed RF bands, and the RF bands where wireless networks operate are full of noisy neighbors.

Licensed radio bands

When a national regulatory body (such as the FCC in the United States) allocates a frequency range to be used for a function, it can also specify how the frequency range can be used or shared.

To use licensed radio bands, a license must be obtained from a government agency. This requirement is true of all users of these radio spectrums. A few of the uses of licensed radio bands are as follows:

• AM broadcast (short wave between 1.711 MHz–30.0 MHz, medium wave between 520 kHz–1,610 kHz, and long wave between 148.5 kHz–283.5 kHz )

• FM broadcast (87.5 to 108.0 MHz)

• Cellular phones (840 MHz)

In the larger electromagnetic spectrum, which includes the radio spectrum, the licensing of infrared and X-ray spectrums also exists.

Unlicensed radio bands

When hearing the term unlicensed, you may think there are no laws or that unlicensed radio bands are like the Wild West and people can do as they like. However, that is not completely the case: You must follow several regulations that cover the use of the unlicensed radio bands. The big difference between licensed and unlicensed bands is that the licensed bands are allowed to be used only by the company that licensed them, whereas the unlicensed bands are used by anyone who wants to use them.

Unlicensed radio bands have been allocated to certain users by the government, but to be able to use and broadcast on these bands, you do not need to have a license; you only need to create compliant devices that are to be used. Regulations exist around these bands, so using unlicensed radio bands is not a free-for-all. In the United States, the FCC regulates all the electromagnetic spectrum, but it has set aside several ranges for public use.

Some of the types of unlicensed radio bands are as follows:

• Industrial, Scientific, Medical (ISM): This type includes several medical monitors and other devices that operate in the 900-MHZ, 2.4-GHz, and 5-GHz bands.

• Unlicensed National Information Infrastructure (U-NII): This type defines the specifications for the use of wireless devices such as WLAN access points and routers in the 5-GHz band.

• Unlicensed Personal Communications Services (UPCS): This type defines the specifications for devices operating in the 1.9-GHz band, where DECT6 cordless phones operate.

Wireless phone companies, such as Sprint and Rogers, have specific frequencies that only they are allowed to use by leasing them from the government. IEEE 802.11 networks have several choices of wireless bands that are available to them to use, without the requirement to lease the frequencies from the government.

The downside of the unlicensed frequencies or bands is that anyone else can use the same frequency ranges, which can cause interference for the signals you are trying to transmit.

So users of both licensed and unlicensed bands are required to follow a series of government regulations, but the unlicensed bands may be used by anyone who follows the guidelines and regulations. These guidelines cover issues like encroaching on neighboring frequencies and causing interference; so if everyone follows these rules, they will all be good neighbors, which is not always the case.

Some groups have helped to develop standards so that all users can be good neighbors with others who use those radio bands. These groups and standards bodies include the following:

• FCC (Federal Communications Commission): Manages and sets standards with regard to the spectrum use

• IEEE (Institute of Electrical and Electronics Engineers): A leading standards organization which publishes standards that are adopted across industries

• Wi-Fi Alliance: An organization that attempts to create a single standard for WLANs, thereby ensuring interoperability

• ETSI (European Telecommunications Standards Institute): Another standards organization that has contributed many worldwide standards

• ITU-R (International Telecommunication Union, Radiocommunication Sector): With the FCC, defines how WLANs should operate from a regulatory perspective, such as operating frequencies, antenna gain, and transmission power

• WLANA (WLAN Association): Provides information resources related to WLANs with regard to industry trends and usage. They are now defunct.

Sending Data Over the Airwaves

There is more than one way to skin a cat (not that I endorse cat skinning), and the same is true about sending data over the airwaves. As you read through this section, you discover the most common methods in use to send data over the air.

When sending data over radio frequencies (RF), remember these details:

• A lot of other traffic is out there, as well as natural phenomena such as atmospheric disturbances and electrical storms (you have to love a good lightening storm) that can cause interference with these signals. Either data sent on the same frequencies or blocked signals can interfere with your wireless communications.

• You need to modify a standard signal to transmit data. There are many standard methods to perform this task. (I show two common methods in the upcoming subsection “Modulating signals.”)

• RF bands are only so wide and can therefore only handle so many discrete sessions or channels at a time. The entire FM radio spectrum has been broken up into 100kHz channels used to assign frequencies to radio stations. This means that there are only so many possible FM channels available for use.

It is not necessary that you understand all the details of signal processing to successfully manage your network, but you should know a few things about signals and their characteristics.

Understanding signals

When referring to a signal in relation to wireless communications, I am talking about an electromagnetic field with specific characteristics, being its oscillation frequency. If I were working with a different medium, the signal could be comprised of light (an optical signal), sound (an airwave signal), or electricity (an electrical signal).

When working with computer data, copper wires are used to send electrical signals; fiber-optic cables can send optical signals. If you want to send wireless signals, you use light waves for line-of-sight technologies (such as IrDA) or RF for non-line-of-sight technologies (such as Bluetooth).

When you listen to a radio station in your local area, this radio station broadcasts its content over a radio-wave signal that operates at a base waveform or wave of a specific set of dimensions consisting of an amplitude, period, and phase. This wave can be modified through one of the modulation techniques (discussed just a bit later in this chapter) to change its form, and thereby transmit information.

All signal waves have the same common characteristics, as shown in Figure 1-1. These are as follows:

• Amplitude: The height of the wave

• Period: The length of the wave to repeat one cycle

• Phase: The offset of the wave from zero or how far a wave is through its cycle

You can measure the amplitude of the wave in many ways: From either peak (peak-to-peak) or from the center of the wave to the peak (peak or semi-amplitude). The frequency of the wave is the number of times it repeats over a given timeframe. There is a good chance you know more about frequencies than you give yourself credit for, because you likely tune your car stereo (or your stereo auto-tunes them for you) to your favorite frequencies on a daily basis to change channels. Those channels are just different spots on that frequency.

Modulating signals

You can now identify a waveform (refer to Figure 1-1) at a frequency. Modulation allows you to add data to that waveform by changing its basic form. The changes that you can make include the amplitude, the frequency, and the phase. In all cases, what you do to the wave prior to transmitting it (modulating) can then be undone by the receiver (demodulating) if the receiver knows what type of modification you are performing. When dealing with computers, which are composed of circuits that are either open or closed, you deal with only two states. As long as you can create two distinct states in the waveform, you can identify them as open or closed, on or off, or 0 or 1. Creating two distinct states then allows you to transmit binary data over RF. Figure 1-2 shows two basic types of modification of the initial carrier wave, which could be used to show binary number patterns.

The two signal modulation techniques that you have likely heard the most about are amplitude modulation (AM) and frequency modulation (FM). The base waveform to which data will be added is referred to as the carrier signal. In the case of broadcasting a radio show, the added information is voices or music, whereas in the case of computer data, it is a series of 1s and 0s that represent binary data.

Introducing RF modulation techniques

In preparation for managing your wireless networks, you should know something about the different RF modulation techniques that are implemented in IEEE 802.11 networking.

You do not have to know everything about them; just be familiar with the terminology that is used in the following sections because it may be helpful when you are trying to find the source of interference or figure out how your network is being affected by interference.

Frequency-hopping spread spectrum (FHSS)

The FHSS modulation technique uses the available channels to transmit and receive data, but rather than staying on any one channel, it rapidly switches between channels using a pseudorandom pattern that is based on an initial key; this key is shared between the participants of the communication session. If interference affects only a few of the channels, this interference is minimized because each channel is used only briefly. If the interference is broad, it can still affect all the channels that are in use. This modulation technique requires that the initial seed or key be shared, but after that has happened, it is very difficult to eavesdrop on.

IEEE 802.11 wireless networks use this technique for modulation, while Bluetooth uses an adaptive version of this technique that stops using channels where interference or weak signals exist.

Direct-sequence spread spectrum (DSSS)

Rather than rapidly switching between several channels, DSSS spreads the carrier signal across the entire 22-MHz frequency range of its channel. For example, a device sending over channel 1 would spread the carrier signal across the 2.401- to 2.423-GHz frequencies (the full 22-MHz range of channel 1). At the same time it is transmitting the data over this channel, it also, at a faster rate, generates a noise signal in a pseudorandom pattern. This noise signal is known to the receiver, which can reverse or subtract the noise signal from the data signal. This process allows the carrier signal to be spread over the entire spectrum. With the entire spectrum being used, the effect of narrow-spectrum interference is reduced. Also, if the channel is being used by other devices, the effect of their signal is reduced because they are not using the same pseudorandom noise pattern.

DSSS has an advantage over FHSS in that it has better resistance to interference. It is used primarily by IEEE 802.11b networks and cordless phones operating in the 900-MHz, 2.4-GHz, and 5-GHz spectrums. IEEE 802.11g/n networks also sometimes use DSSS, but these newer networks tend to prefer orthogonal frequency division multiplexing (ODFM).

Orthogonal frequency division multiplexing (OFDM)

The slower that data is transmitted, the less likely that interference or line noise will cause a problem with the transmission. Multiplexing allows you to take several pieces of data and combine them into a single unit that can then be sent over the communication channel. In this case, OFDM takes the data that needs to be transmitted and breaks it into a large number of subcarrier streams (up to 52 subcarriers) that can then all be multiplexed into a single data stream. Because 52 subcarriers exist, the final data stream can be sent at a slower rate, while still delivering more data than other methods in the same time period.

This multiplexing process gives OFDM an advantage over DSSS because it allows higher throughput (54 Mbps instead of 11 Mbps), and it can be used both in the 2.4-GHz frequency range and in the 5-GHz frequency range. Multiplexing has many uses, and OFDM is used in any technology that needs to send large amounts of data over slower transmission lines or standards. OFDM is used with IEEE 802.11g/a/n networking as well as with ASDL and digital radio.

Multiple-in, multiple-out (MIMO)

MIMO allows multiple antennas to be used when sending and receiving data. The concept of spatial multiplexing allows these multiple signals to be multiplexed or aggregated, thereby increasing the throughput of data. To improve the reliability of the data stream, MIMO is usually combined with OFDM. When using multiple antennas, you can achieve higher transmission speeds — over 100 Mbps.

MIMO is used in both WiMAX and IEEE 802.11n networks and is the largest reason these networks achieve their high speeds.

Battle of the Bands

Early in WLAN development, many people were trying different technologies to achieve the goal of wireless LAN communication. As some clear winners started to emerge, a need existed for interoperation among these technologies. This desire for interoperation led to the development of standards around WLAN communications.

As with all other standards in communications, the WLAN standards allow all companies involved to build equipment to a level that allows their equipment to be used with (or to interoperate with) equipment made by other vendors. Interoperability was not necessarily true in the beginning, but by the time IEEE 802.11a and IEEE 802.11b emerged, the standards were set and all hardware vendors were able to build to a level that allowed interoperability.

Checkin’ Out the 2.4-GHz band

Many of the wireless standards that have emerged were designed to operate in the already crowded 2.4-GHz band. Whether this was a good idea does not matter; it is what happened.

When working with the 2.4-GHz portion of the RF spectrum, the actual range that you are working with is 2.4000–2.4835 GHz. This range is broken up into 14 unique channels, with each one 22 MHz wide, but the center of each of these channels is only 5 MHz apart. Therefore an overlap exists between consecutive channels, which results in interference and prevents proper communication. In the United States, the FCC has allowed only 11 of these channels to be used, while countries like Japan have allowed all 13 channels to be used. Why? You would have to write to the FCC to find out.

Due to the overlapping of channels, if you are using multiple devices in a small geographical area where the devices’ RF might come in contact with each other, you can choose from a maximum of four nonoverlapping channels — 1, 6, 11, and 14. Figure 1-3 shows how each of the 14 channels defined in the range overlap, while only channels 1–11 are used in the United States and many other countries, reducing those countries to only three nonoverlapping channels.

The 2.4-GHz RF band is used by IEEE 802.11 b/g/n networking, as well as Bluetooth and many cordless phones. This situation has caused issues because, in any given area, you can expect something to generate signal traffic in that frequency range. Poorly designed devices can bleed beyond their specified RF ranges and create additional interference for other devices. The 2.4-GHZ RF band is heavily congested with both properly and improperly designed devices.

The following sections take a closer look at the standards in this category.

IEEE 802.11

As with the early days of any technologies, a number of players in the industry were looking at different methods of transferring LAN data without wires from early on. As things moved along, a few groups emerged at the top of the pile. These groups used technologies that were not compatible with each other, and the most popular of these was collectively called 802.11-1997 or sometimes 802.11 Legacy. It is odd that this mash of wireless was associated under one name, because they were not compatible with each other. The common factors of this standard were the communication rates and base technology components that are common to all IEEE 802.11 networks.

Relevant jargon

Terminology that arose from this specification applies to all IEEE 802.11 networks. This terminology includes the following:

• Access point (AP): A device that allows wireless devices to access the physical network.

• Basic Service Set (BSS): A collection of a single AP and its associated client devices or stations (STA) form a BSS.

• Distribution System (DS): The interconnection of AP through wired media or wirelessly. When used wirelessly, this is called a Wireless Distribution System (WDS).

• Extended Service Set (ESS): One or more BSSs that are interconnected and appear as a single BSS.

• Service set identifier (SSID): An identifier for a BSS or ESS.

• Distributed Coordination Function, which is carrier sense multiple access collision avoidance (CSMA/CA): A method of sharing a single wireless channel by more than one STA.

• Dynamic rate shifting (DRS): Adjusts the transmission rate of a wireless channel based on the channel condition. The channel condition would be based on how strong or clear the wireless signal is.

• Beacon frames: A wireless management frame periodically sent over the wireless network.

• Wired Equivalent Privacy (WEP): Security and encryption standard for wireless networks.

• Ad hoc networking: A wireless network that does not have an AP.

• Infrastructure networking: A wireless network that has an AP.

These terms are fully described in the later chapters of this minibook, but I want to make you aware that they date back to the first IEEE 802.11 wireless networks.

How IEEE 802.11 works

While there is an alphabet soup of acronyms associated with 802.11 wireless networking, I want to start off by telling you about some of the specifications which define 802.11 networks. The specifications for IEEE 802.11 define three possible physical layer systems that could be used:

• Frequency-hopping spread spectrum (FHSS) in the 2.4-GHz band

• Direct sequence spread spectrum (DSSS) in the 2.4-GHz band

• InfraRed (which is in the specification but was not adopted by the industry)

In addition to defining the physical layer protocols, the specification defines the communication speed as 1or 2 Mbps.

The main benefit of IEEE 802.11 was that it offered RF wireless networks with greater range and throughput than other wireless technologies at the time, which were primarily infrared-based and thereby line-of-sight. Because this networking was based in the crowded 2.4-GHz spectrum, a great deal of interference existed, which was only partly minimized by FHSS and DSSS.

All the IEEE 802.11 networking standards use carrier sense multiple access collision avoidance (CSMA/CA). This collision mechanism is different from the Ethernet LAN standard, which uses carrier sense multiple access collision detect (CSMA/CD). In both cases, carrier sense means that all devices can sense or see other traffic that is transmitting, and multiple access means that multiple (or all) devices can access the media at the same time, but only one computer is allowed to send data at a time. (You can read more about both CSMA/CA and CSMA/CD in Book I, Chapter 4.)

Differences between LAN and WLAN technologies

The media over which data is sent is dramatically different between a wired LAN and a wireless LAN. Due to this difference in media, there is a difference between how the two types of LANs interact with the media. With wired LAN technologies, when a computer wants to send a frame out on the network, it does the following:

1. It uses its carrier sense to see whether anyone is using the network.

2. If not, it then sends a network frame out onto the wire and the signal goes to the end of the wire, where it bounces and returns to the sending computer. The maximum length of an Ethernet cable is set to require the bounce signal to return within a specified time limit.

3. When the computer sees what it sent, the computer knows that it was sent without a collision. But if what the computer sees is garbled, it knows that a collision occurred, and it then waits a random period of time and repeats the process.

This system of collision detection works because the physical media allows the sending computer to verify that its data was correctly sent on the media.

When working with WLAN technologies, here is what happens:

1. The frame is sent on the network, which has no mechanism to allow a signal to bounce, and as such, it relies on collision avoidance.

2. The method of sending data still starts with listening to the network to see whether anyone is using the media.

3. If no frames are detected for a specified period of time (known as the distributed interframe space [DIFS]), it is allowed to send its frame.

4. The receiving station performs the CRC (cyclic redundancy check) of the received packet and sends back an ACK (acknowledgment) frame when the media is free.

5. After the sending station receives its ACK frame, it knows that the data was sent correctly.

This collision-avoidance process generates more network frames to send data, but it follows a more orderly process than collision detection.

When the network is under high utilization, the collision detection process tends to move more data than collision avoidance; this is likely due to mandatory wait states that occur by devices honoring the DIFS.

Dynamic rate shifting (DRS) allows an AP to rate-shift to a lower bandwidth when the signal weakens. The signal becomes weaker proportionally to the distance between the AP and the target wireless device. In other words, the farther you go from the AP, the weaker the wireless signal becomes and the lower the transmission speed becomes because DRS automatically rate-shifts to a lower speed when the signal weakens.

IEEE 802.11b

In the 2.4-GHz spectrum, the first major upgrade to the WLAN specification is IEEE 802.11b, which raised the maximum bandwidth to 11 Mbps. This standard also relied primarily on Complementary Code Keying (CCK) as its modulation technique, which was a modified form of DSSS, while it would use DSSS when using slower connection speeds via DRS. The typical range for IEEE 802.11b is about 100 feet (30 meters) when operating at 11 Mbps.

The benefit of this standard over its predecessor is primarily in the maximum network speed, while IEEE 802.11b still suffered from interference on a crowded RF spectrum. The other drawback that the IEEE 802.11b standard suffered from was a slower transmission speed than the other standard at the time (IEEE 802.11a, which had a rated bandwidth of 54 Mbps). Even though IEEE 802.11a had higher throughput, IEEE 802.11b emerged as the dominant standard due to timing and market forces.

IEEE 802.11g

The next major improvement in WLAN networking in the 2.4-GHz band is IEEE 802.11g, which increases the maximum bandwidth to 54 Mbps and primarily makes use of the RF modulation technique of orthogonal frequency division multiplexing (OFDM) in addition to CCK and DSSS when speeds are reduced.

IEEE 802.11g offered an easy upgrade path for users of IEEE 802.11b as older devices were able to connect to newer radios, although this upgrade caused the radio to automatically fall back to the slower technology for all users. This issue was mitigated by many hardware vendors by including multiple radios in their APs, allowing one to be set to IEEE 802.11g only and one to be set to IEEE 802.11b. When using IEEE 802.11g transmission standards, a modified collision avoidance system is used, thereby reducing the delays and the wait states required for transmission.

Keep on Rockin’ with the 5-GHz band

When working with the 5-GHz portion of the RF spectrum, you are primarily working with the range of 5.170–5.835 GHz. This range is broken up into 24 unique channels, with each one being 20 MHz wide and the center of each channel is at least 20 MHz apart. 5-GHz allows 24 unique conversations or communications to take place in that frequency range in the same physical area. If you are using IEEE 802.11a wireless networking, in a single room, you could operate 24 access points without interference between devices (not that you would likely want to do that).

In terms of wireless networking standards on the band, at the same time that IEEE 802.11b was being implemented in the 2.4-GHz RF band, IEEE 802.11a was being implemented in the 5-GHz band. IEEE 802.11a offered several advantages over IEEE 802.11b. It had a maximum transmission rate of 54 Mbps and operated in the less cluttered 5-GHz RF band. It uses OFDM as its RF modulation technique. Due to time to market and many other issues, this superior wireless technology took a backseat to IEEE 802.11b, which was vying for market position at the same time. (This situation seems to have been similar to the Beta-versus-VHS war that keeps repeating with new technology participants.)

The biggest drawback is that IEEE 802.11a is not compatible with devices that run in the 2.4-GHz spectrum, primarily IEEE 802.11b/g devices. The biggest benefits of the 5-GHz portion of the spectrum are the nonoverlapping channels and the lack of competition for channel space, as in addition to IEEE 802.11a/n networking, this RF band is primarily used only by cordless phones. Additionally, cordless phones in the 5-GHz spectrum honor the same non-overlapping channel designations as IEEE 802.11a, which causes less interference with the WLAN.

Most countries use 20-MHz wide channels but often authorize different frequencies to be used for the channels that could go as low as 4.905 GHz. For simplicity, I limit my discussion to the authorized channels in the United States.

For an IEEE 802.11a wireless network, the list of channels has been reduced by the FCC to 12, which are only channels 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, and 165. Now following the standard gets more confusing when dealing with IEEE 802.11n, because the specifications for the standard allow the use of either 20-MHz channels or 40-MHz channels; the increase to 40-MHz channels allows for double the amount of data that can be sent over any one channel.

Technologies that support the 2.4-GHz and 5-GHz bands

The latest technologies for WLAN allow you to operate in both of the major RF frequencies. Being able to choose either frequency when operating the WLAN provides you with the best of both worlds and will likely be the trend moving forward. Right now the only relevant specification is IEEE 802.11n. In early versions of the draft specifications, this standard was only to use the 2.4-GHz RF spectrum. However, the final specification, ratified in September 2009, allowed operating in the 5-GHz RF spectrum as well. By allowing both of the previous RF spectrums to be used, it allows IEEE 802.11n devices to be backward compatible with both IEEE 802.11b/g and IEEE 802.11a devices and maximizes its possible acceptance in a network setting.

IEEE 802.11n uses both OFDM and MIMO RF modulation techniques. Although ranges are comparable with the IEEE 802.11 network specifications, it allows a maximum throughput of 600 Mbps when using four MIMO streams, or 150 Mbps for a single stream.

IEEE 802.11n offers many advantages over the previous IEEE 802.11 network specifications because it operates in both major RF bands, is backward compatible with other standards, and operates at higher data speeds.

Because it has only recently been ratified, many of the existing devices on the market conform to draft specifications, but you can expect that if you have any of these, a firmware-based upgrade to the final standard should be released soon.