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Wireless Basics

{mospagebreak toctitle= Introduction}

Introduction

It's been a few years since our first Wireless Need to Know series and lots has changed. So we thought it was well past time to bring it up to date to better reflect the wild, and wide, world that wireless networking has become.

There's a lot to know about wireless networking

Let's start right out with our Three Rules of Wireless Networking:

The three rules of Wireless Networking
1) It never goes as fast as they say it does
2) It never goes as far as they say it does
3) It never sets up as easily as they say it does

These Rules aren't intended to discourage you, but more to prepare you for a successful and satisfying wireless networking adventure. Let's dig into each of the Rules and see what's behind them.


Rule #1: It never goes as fast as they say it does

Since manufacturers know that people buying computer gear like to compare numbers, and that bigger numbers are usually more attractive than smaller numbers, they're more than happy to oblige! So they make sure you see the biggest throughput number that they can quote on all their marketing literature.

Tip! Tip: "Throughput" or "transfer rate" is the number of bits that move from one place to another in a given period of time. For wireless networking equipment, throughput is usually quoted in Mbps (Megabits per second).

This number, however, is usually the raw data rate, and is something that you'll never approach in your actual network. What number can you use? The answer is Rule 1A:

Rule #1A: Take the manufacturer's Mbps number and divide by (at least) two.

This means that for the most popular wireless networking standard right now (802.11g), you take the 54 Mbps quoted number, divide by two, and get 27 Mbps. This would be the fastest speed that you'd most likely experience on your network, under best-case conditions. (We'll explain what we mean by "best case conditions" later, when we talk about Rule #2.)

And truth be told, in actual use, you'll be lucky to get about 40% of whatever number you see prominently displayed on the front of the product box.

"Enhanced" modes that have been added to 802.11a, b and g products promise even higher speeds, although they usually throw in a caution that all of your equipment has to come from the same manufacturer for the higher speeds to work. These "turbo" modes actually, do work, but are worth a rule of their own:

Rule #1B: You can't depend on quoted "Turbo" or "enhanced" mode speeds in mixed networks.

The main reason for this rule is that speed enhancement techniques rely on working with their own kind in order to maximize network speed. Even though the most popular 802.11g techniques - Broadcom's AfterBurner, and Atheros' Super-G - use some of the same speed-enhancement techniques, they are implemented differently and therefore aren't interoperable. And when the techniques don't work, the products default back to using the standard (and slower) 802.11g protocols that they must be able to implement.

Tip! Tip: Broadcom and Atheros are manufacturers of the wireless chipsets found in many wireless products.

And, thanks to the marketing folks at your favorite manufacturer of networking products, even when the same speed-boosting techniques are used, the names are changed so that you, the consumer, can't tell that they are the same.

For example, Broadcom's AfterBurner technology is called "SpeedBooster" by Linksys, and "125* High-Speed Mode" by Buffalo Technology. Products using Atheros' Super G chips are a little easier to keep track of, since most manufacturers either use "108 Mbps" somewhere in the product name or even use the actual "Super G " term somewhere in their product literature.


Rule #1 - more

By the way, pretty much all of that missing throughput in Rule 1A is used to make sure all of your data gets from one place to another without any dropped bits. This overhead - which all communication protocols have - is heavier in wireless networking due to the tougher environment that data has to travel through.

As disappointing as losing half your throughput may be, you may never notice it in a small wireless network. It all depends on how many wireless clients you have, and what their data transfer requirements are. Here are a few scenarios for comparison.



Case 1: Probably won't notice

  • One to two wireless clients
  • Occasional file and print sharing
  • Network used mostly for Internet web browsing, email, instant messaging
  • Internet connection via dialup

Explanation: These applications generally don't require high transfer rates for extended periods of time. Even if they did, the slow Internet connection is going to be the main factor in determining your effective client throughput.

Case 2: Might notice

  • Three to four wireless clients
  • Occasional large Internet downloads
  • Light local network file and print sharing
  • One or two Internet audio streams
  • One video stream

Explanation: With more wireless clients sharing the same relatively small bandwidth, the chances of more than one client wanting a large chunk of bandwidth at the same time are increased. Add the higher bandwidth requirements of audio and video streams and file and printer sharing, and your wireless users might occasionally notice some sluggishness on the network.

Note that I don't mention the Internet connection method as a wireless performance factor. Unless you live outside the United States where speeds in the 10's of Mbps are common, or are lucky enough to live in areas where Verizon is rolling out its FIOS optical fiber-based service, your broadband connection probably tops out at somewhere between 1.5 to 5 Mbps. This is well below the typical speeds found in wireless networks.

Case 3: Definitely will notice

  • More than four wireless clients
  • Frequent large Internet file downloads
  • Heavy local network file and print sharing activity
  • More than one video stream
  • More than two simultaneous audio streams

Explanation: More clients + larger data transfers = Frustrated users!

The other key factor that can affect the speed of your wireless network is enabling WEP encryption. WEP (Wired Equivalent Privacy) is a much maligned, but still useful, feature of 802.11 wireless gear that is intended to keep your wireless data private, and involves the use of an encryption algorithm. The encryption algorithm requires some fairly hefty number crunching, which some wireless adapters have trouble keeping up with. In some cases, enabling WEP encryption can cut your throughput by 50 to 60%. Note that while this problem has largely been eliminated in current 802.11g products, it can still be found in some products.

The most prefered solution is to use the more secure WPA (Wi-Fi Protected Access) or WPA-2 wireless security if your adapter supports them. But if your adapter doesn't, you should either enable WEP and take the throughput hit or buy a different adapter. No one should run an unsecured wireless network unless they intend to freely share their network resources and have properly secured clients and network shares from unauthorized access.


Rule #2: It never goes as far as they say it does

Perhaps the biggest frustration that new wireless networkers encounter is finding that the range of their wireless network is nowhere near what they thought it would be. Part of the problem is the same "bigger numbers are better" approach that is used for throughput specs.

But where no manufacturer would dare quote a number higher than 54Mbps for unenhanced, i.e. standard-compalient 802.11g throughput (since that number is set by the 802.11g specification itself), there is no "standard range" number for 802.11 products, and manufacturers have much more leeway in the numbers they advertise.

As a result, the range numbers you'll see quoted from various manufacturers vary widely... so widely, in fact, that there is another rule for using them:

Rule 2A: Don't buy wireless equipment based on a manufacturer's range specifications.

I've come to the above conclusion after testing many wireless products and finding little correlation between the advertised and actual range. Unfortunately, the only effective way to know how a piece of wireless networking gear will perform is to try it in your environment. It also helps to have a basic knowledge of the way that high frequency radio waves work and basic range-enhancement techniques. See our Wireless LAN Performance Improvement Need To Know for more info.


Rule #3: It never sets up as easily as they say it does

This rule might be a general rule for anything related to computing in general, but I include it in case you think that Microsoft Windows XP has cracked the code on making installing a wireless network a painless experience.

With wireless networking, you'll still probably run into the usual suspects of outdated, corrupted, missing, or mismatched drivers, balky Windows installations, and cryptic, incomplete, or conflicting installation instructions. And don't get me started about the totally confused mess that manufacturers have made of marketing and educating users on wireless bridging and repeating products! Fortunately, we're here to help on that subject with the Wireless Bridging Need To Know and Setting up WDS Bridging / Repeating How To.

But you'll also find it useful to have some idea of the construction materials used in your home or small office, be willing to understand how high-frequency radio waves travel, and to be flexible as to where you install your wireless networking equipment.

Now that you understand the rules of the game, we'll next look at what your choices are for Wireless Networking technologies.


Wireless Technologies - 802.11b

We've come a long way since 2001, when the only choices available for wireless networking were the now-defunct Home RF and 802.11b. Flash forward to today and it seems like a new wireless technology or variation on an existing one appears every week. But when you peel away the proprietary boosting and stretching technologies that manufacturers have tacked on, you'll find that the actual number of standards-based technologies is smaller than you might think. Let's start with 802.11b.

Technology Summary

The standard that started the "Wi-Fi" explosion, 802.11b operates in the 2.4GHz unlicensed frequency band (same as the one used by 2.4GHz cordless phones and microwave ovens), and uses DSSS (Direct Sequence Spread Spectrum) modulation. It has a maximum raw data rate of 11Mbps, with fallback rates of 5.5, 2, and 1Mbps.

802.11b was the first technology to be widely deployed and is still found in thousands of businesses and public Wi-Fi hotspots. For the most part, 11b has been eclipsed by the faster 802.11g, which leads the consumer, if not enterprise wireless networking market. However, 11b is still found in Wi-Fi phones, streaming music adapters, PDAs and other cost-sensitive applications where network speed requirements are lower.

Enhanced versions

Texas Instruments introduced an "enhanced" 802.11b in the first half of 2002 in the form of its ACX100 chipset, which used TI's PBCC (Packet Binary Convolutional Coding) modulation technique to boost the raw data rate from 11Mbps to 22Mbps. This advance was very popular and helped TI win some business from then market-leader Intersil. But the appearance of draft-802.11g products brought its rise in popularity to an abrupt halt. But not before versions claiming 44Mbps speeds also made a brief appearance.

Positives

  • The most widely-available WLAN standard
  • Relatively inexpensive

Negatives

  • Susceptible to interference from 2.4GHz cordless phones, microwave ovens and Bluetooth devices
  • Susceptible to interference from neighboring wireless LANs due to only three available non-interfering channels available

Recommendation: 802.11g is a better choice and is backward compatible with 11b


802.11g


Technology Summary

802.11g's claim to fame is 54Mbps raw data rate with 802.11b backward compatibility. The higher speed comes from using the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme that first was used in 802.11a. Backward compatibility comes from staying in the 2.4GHz band and supporting the Complementary Code Keying (CCK) modulation scheme used by 802.11b.

This second point is important, because every 802.11g product actually can automatically fall back to operating in 802.11b-only WLANs as well as mixed b/g and 11g-only.

This standard first took the consumer WLAN market by storm, even before the standard was released and "draft" 802.11g products started appearing, aimed squarely at consumers seeking higher wireless speeds. Once the standard was ratified, enterprise grade gear made the transition and today (early 2006) 11g is the wireless LAN market leader, primarily based on its good cost vs. performance.

Despite manufacturer's claims to the contrary, 802.11g products are generally not suited for streaming video. The problem is not speed, since enhancement techniques generally provide bandwidth to spare. The problem comes from 11g's use of the overcrowded 2.4GHz band. Most consumers just do not have a quiet enough RF environment to enjoy trouble-free wireless video. Audio streaming may be possible due to its very low (100's of kHz) bandwidth requirements, but again, success is highly dependent on environment.


Enhanced versions

There are two primary enhancement technologies for 802.11g products. Broadcom's 125* High Speed Mode (which started out as "Afterburner") works by removing as much overhead as possible from 11g transmissions. The main techniques used are data compression, and "frame bursting" (sending more data packets in the time allowed) with some other overhead-reduction techniques thrown in.

As mentioned earlier, products using this technology sometimes use the 125* High Speed Mode moniker directly, although Linksys prefers its own "SpeedBooster" branding.

The second enhancement technology is Atheros' Super-G (and Super-AG for its dual-band products), which is clearly described in this whitepaper (PDF link). Super-G starts with similar frame bursting, compression and overhead reduction techniques as Broadcom, but added a controversial "turbo" mode.

"Turbo" (now officially dubbed "Dynamic Turbo") combined two channels in order to boost real, application-level throughput as high as 50Mbps. But it did it at the expense of interfering with neighboring "legacy", i.e. 802.11b and g WLANs. Although Atheros was forced to modify the "turbo" mode behavior many times so that it didn't cause interference, it is thought that Super-G based products still wreak havoc in areas where wireless LANs are closely spaced.

Products using Super-G typically either use the term directly or somewhere quote its telltale "108Mbps" maximum data rate somewhere in the product literature.

Generally, you can achieve some throughput enhancement even when mixing products from different vendors, as long as you mix products using the same enhancement technology. But products will fall back to standard 11g speeds if you try to mix Super-G and 125* High Speed Mode gear.

A final note on enhancements is that both Broadcom and Atheros also have range enhancing technologies that you'll sometimes run across in products. Since specifying range is something that manufacturers would rather not do, they tend to play down these technologies. But for the record, Atheros calls theirs eXtended Range (XR) and Broadcom opted for BroadRange. Once again, you can download an Atheros XR whitepaper, but good luck trying to find something similar from Broadcom.

Positives

  • Widest range of product types
  • Relatively inexpensive
  • Effective throughput and range enhancement technologies available

Negatives

  • Susceptible to interference from 2.4GHz cordless phones, microwave ovens and Bluetooth devices
  • Susceptible to interference from neighboring wireless LANs due to only three available non-interfering channels available
  • Heavy reliance on non-interoperable enhancement technologies
  • Hard to tell what flavor of enhancement you have

Recommendation: If you're buying wireless today, you'll probably choose 802.11g.


802.11a and Dual-Band


Technology Summary

This standard debuted in late 2001. Its main attractions are that it operates in the less crowded 5GHz frequency band, and has a maximum data rate of 54Mbps. It was the first 802.11 standard to use OFDM, which is key to achieving the 54Mbps data rate. It has thirteen non-interfering channels - 8 lowband and 5 highband (though not every card supports the highband channels) vs. three for 802.11b, making it easier to set up large, multi-AP installations.

First-generation 11a products suffered from shorter range than 802.11g products and developed an "inferior range" reputation that still seems to dog the technology today. But the problem was eliminated in second-generation products (see our Second-generation 802.11a NTK for more info), such that there is little difference in range between standard, i.e. unenhanced 11a and 11b/g products.

Consumers will need to hunt for 802.11a-only products, but there is little reason to do so. Dual-band products that cover all three standards (11a/b/g) are more widely available and much more flexible. They're actually less expensive than 11a-only products, which are now manufactured mainly for enterprise use and special applications. But dual-band products are still harder to find, since manufacturers seem to have a love / hate relationship with them.

Dual-band briefly seemed poised for a comeback in late 2004 when manufacturers started to make a simiplistic pitch of "11b/g for data, 11a for multimedia". But once faster "pre-N" products started to appear, they all seemed to shift back to pitching those (2.4GHz) products for multimedia streaming.



Enhanced versions

Atheros has virtually owned the 802.11a chipset market, so you'll find the same throughput and range enhancements as Super G, but called "Super AG". The good news is that, unlike 802.11b/g, 802.11a doesn't have overlapping channels. So although Super AG's "Turbo" mode takes up two channels, there are plenty more for neighboring users to change to to avoide interference.

Positives

  • More non-interfering channels than 802.11b/g
  • Less likely to run into interfering neighboring WLANs
  • Neighboring WLANs can tune away from "Turbo" users

Negatives

  • Products are more expensive
  • Not as wide a range of products available

Recommendation: 11a products can help avoid interference from 2.4GHz cordless phones, microwave ovens, and neighboring wireless LANs. Definitely worth considering if any of these problems are bothering you, or if you want to try streaming wireless video. Don't be tempted by cheap 11a-only products on eBay, though, since you'll most likely be getting products using first-generation chipsets, which have inferior range.


Bluetooth



Technology Summary

Bluetooth is not really intended to be a wireless LAN (WLAN) technology, but aimed at providing nearly automatic connectivity among small groups of devices without a formal network infrastructure. Think of it as something that could wirelessly enable your PDA to print to a nearby printer, or your connect your cell phone to a headset. Bluetooth's primary advantages over wireless LAN technologies are its lower power consumption and easy set up (at least in theory). Its weaknesses are that it can be a bit too promiscuous in allowing connectivity and its low data rate - 721 kbps normally, but up to 2.1Mbps for Bluetooth 2.0's Enhanced Data Rate (EDR).

Bluetooth uses Frequency-Hopping Spread-Spectrum (FHSS) and operates in the same 2.4GHz band as 802.11b/g devices. FHSS is a spread spectrum modulation scheme that uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. So 802.11b/g devices can't understand Bluetooth transmissions, which appear as yet another noise source. There can be an unlimited number of devices in a Bluetooth network (called a "piconet"). But only eight (1 master plus 7 slaves) can be active at a time.

This technology has had a rough birthing process, but seems to finally found its groove for getting rid of wires for keyboards, mice and headsets. (The wireless Bluetooth headset market actually has three segments: consumer audio, mobile phone/PDA, and computer, each with different physical designs.) But all of Bluetooth's problems are not behind it. Windows support - even in XP2 - remains a mess and user interfaces are still evolving.

One of the key troublemakers is the large number of profiles that Bluetooth devices can (or more often cannot) support. Just finding an up-to-date list of the profiles is a real job. Here's the one on wikipedia, which looks to be relatively up to date. This Bluetooth Profile dependency diagram on palowireless is also helpful in sorting out the relationships among the profiles. Although some profiles may not make sense for certain devices, you'd better hope the general-purpose Bluetooth adapter that you purchase for your desktop or notebook supports them all - or at least the profiles required by the device that you want to connect to!


Enhanced versions

There aren't really any non-standard enhancements to Bluetooth, although there are five versions of the standard - 1.0, 1.0B, 1.1, 1.2 and 2.0 - and three Classes (or power levels). Most devlces you'll find are either Class 1 (100 mW) or Class 2 (2.5 mW), with Class 3 (1 mW) devices mainly found in SD card form or embedded into devices.

Note that some manufacturers have also developed proprietary profiles.

Positives

  • Simple peer-to-peer low-speed wireless networking
  • Low power consumption

Negatives

  • Not all adapters support all profiles
  • Default settings can be a security risk
  • Can cause interference with 802.11b/g WLANs

Recommendation: Not useful to construct a WLAN, but very handy for getting rid of wires, especially in mobile and VoIP applications.


802.11n (Pre-N and MIMO)



Technology Summary

802.11n is an upcoming standard that will add throughput enhancement to existing 802.11 standards. The goal is to have an IEEE standard (instead of the current proprietary enhancements) that supports wireless throughput over 100Mbps.

11n will be DSSS-based and, like 802.11g, use OFDM as part of its speed-boosting arsenal of tricks. But it will also use Multiple Input Multiple Output (MIMO) technology to boost speeds well above the 100Mbps target.

This much-awaited and long-delayed standard passed a major milestone in January 2006, when warring factions submitted a compromise draft standard proposal to the IEEE Task Group N, which quickly accepted it. This ended a long battle between the two main groups, World-Wide Spectrum Efficiency (WWiSE), backed by Texas Instruments, Motorola and Airgo Networks and TGn Sync, backed most notably by Intel.

Somewhere between 802.11g and 11n are products that manufacturers started pumping out in late 2004. These products used chipsets from Airgo Networks and employed MIMO technology to achieve high speeds similar to products using Atheros' Super-G "Turbo" mode, but without the interference with neighboring wireless LANs. See this review of the Linksys Wireless-G Broadband Router with SRX for more details.)

These products established a unique category of products that came to be known as "Pre-N" or more commonly MIMO, since the Wi-Fi Alliance quickly threatened to withdraw certification from any companies trying to market products as "draft 11n". Never wanting to miss a trend (or chance to foist upgrades on an unwitting public) manufacturers began pumping out "MIMO" products a'plenty throughout 2005. Since MIMO can be implemented in a variety of ways, products using chipsets other than Airgo's appeared, with varying levels of performance. (See our MIMO Face-Off for a comparative review of eight "MIMO" products".)

Now that there is an official draft 802.11n standard, the latter half of 2006 will see a number of "draft 11n" products hit the market. It's interesting to note that the upcoming chipsets from Atheros, Broadcom and Marvell all are dual-band designs (Airgo's has been dual-band from the start). But, at least until now, consumer-level "MIMO" products have stuck with operating in the 2.4GHz band only.

One final note is that 802.11n products will use a 40MHz bandwidth, which is double the 20MHz bandwidth used by 802.11b and g products. This 40MHz bandwidth will be needed to deliver more than 100Mbps of application level throughput. Our test of NETGEAR's RangeMax 240, which uses an early form of 40MHz bandwidth technology based on Airgo's third-generation chipset, showed interference problems with 802.11b/g products operating on Channel 6. So 11n could prove to be a not-so-welcome addition to wireless neighborhoods.



Enhanced versions

None yet since there is no standard.

Positives

  • Backward-compatible with existing 802.11a/b/g technologies
  • Application level throughput of over 100Mbps (under best-case conditions)
  • Can operate in both 2.4 and 5 GHz bands

Negatives

  • Expensive
  • Can interfere with "legacy" 2.4GHz products
  • 2.4GHz products still susceptible to cordless phone, microwave, etc. interference

Recommendation: 11n-based gear is probably in your future. But current "MIMO" products are not upgradeable and don't count on early "draft 11n" products being upgradeable either. Best to wait until late 2006 if 11n upgradeability is important to you. Otherwise go ahead and buy if you really need high wireless speed and range.


Wireless MAN / WiMAX (802.16/16a)



Technology Summary

WiMAX isn't really a wireless LAN technology, but a family of long-distance wireless standards intended for "last mile", wireless ISP and backhaul applications.

802.16-2004 is a released standard, addressing fixed wireless systems. The mobile version, 802.16e has also been approved for release and is scheduled to be published in February 2006.

The WiMax Forum is the compatibility and interoperability certification industry group that is the equivalent of the Wi-Fi Alliance.

Recommendation: Interesting if you're running a wireless ISP. But otherwise, leave this stuff to the enterprise guys.


UltraWideBand (UWB) and ZigBee

Like WiMax, neither UWB, nor ZigBee are suited for building a wireless LAN. But you hear about them a lot, so here are a few key factoids.

Although this technology has been around since the 1960's, UWB has captured the imagination of many who closely follow the wireless networking market. But some of the initial buzz is fading as the first UWB devices hit the market in early 2006.

UWB employs spread-spectrum technology, in perhaps its most extreme form. UWB signals look more like noise than typical modulated radio signals since they are spread out over several GHz and operate at low power levels. The technology has been controversial, however, with some groups concerned that the signals could interfere with other wireless services.

Despite these concerns, the FCC approved UWB for commercial use in late Feb 2002. In a nod to the concerns mentioned above, however, the FCC set limits on the frequencies that UWB devices could use, avoiding frequencies used by the military and GPS devices. Power levels were also limited to keep useful operating range down to about 10 Meters / ~33 feet.

But similar to the battles over the 802.11n standard, UWB has had a difficult birthing process. At the beginning of 2006, the working group for the relevant IEEE standard, 802.15.3a, gave up trying to fight the warring UWB Forum and WiMedia Alliance industry groups and voted to disband. The result is that members companies of both groups are moving forward with bringing non interoperable products to market.

And to make matters worse, the first products from both groups are aimed at eliminating USB cables. "Cable-free USB" products based on technology from Freescale Semiconductor (in the UWB Forum camp) will hit in late spring this year (2006). Then "Wireless USB" products from WiMedia alliance member companies are expected to follow in the second half of 2006. (See this CES 2006 report). Both technologies are aiming at USB 2.0 speeds (480Mbps), but will be able to support single links only.

ZigBee is another "Personal Area Network" (PAN) Bluetooth-like technology, operating at about 1/4 Bluetooth's 1Mbps maximum data rate, and consuming very low power. The official IEEE 802.15 Task Group 4 website puts it this way:

... a low data rate solution with multi-month to multi-year battery life and very low complexity. It is intended to operate in an unlicensed, international frequency band. Potential applications are sensors, interactive toys, smart badges, remote controls, and home automation.

ZigBee is a ratified (released) standard and is finding its first applications in home automation, control and security applications

Recommendation: UWB and Zigbee are more of a threat to Bluetooth than Wi-Fi. Not suited for building a wireless LAN.