802.11g versus 802.11a

New Wireless tech promises 54 Megabits of data per second -- and delivers about 22.

Introduction

One of the most heavily hyped new technologies to emerge at the Comdex trade show in Nov. 2001 was a high-end variant of the 802.11 "Wi-Fi" wireless standard. Dubbed 802.11a, its backers touted 54 Mbps data rates -- and, claimed that, via a special "turbo mode," peak rates up to 72Mbits of data per second could be achieved. Industry pundits began proclaiming 802.11a the next-generation wireless networking standard. One little problem, they noted: it isn't backward-compatible with the widely used 802.11b standard.

Around the same time (Nov. 15, 2001, to be exact) the Institute of Electrical and Electronics Engineers (IEEE) tabled a working draft of a competing specification after a reportedly difficult arbitration process. Dubbed 802.11g, its most significant advantage was the fact that, unlike 802.11a, it was fully backward-compatible with the older 802.11b standard. 802.11a is compatible with neither 802.11g nor 802.11b. Manufacturers lined up on both sides, with some sidestepped the compatibility issue by promising to develop dual-standard wireless Access Points, capable of interoperating with wireless cards using either standard.

Fast Forward to 2003: 802.11a -- now called WiFi5 -- and 802.11g are both available in the market. The latter was released as a draft standard after lengthy delays, reportedly caused by disagreements between TI and Intersil --and beefed up from its originally planned 22 Mbps data rate. Some 802.11g proponents, including Microsoft, have delayed bringing 802.11g products to market until the standard is ratified -- a move that finally happened on June 12. (The month of May saw the release of a controversial "final draft," detailed below.) Analysts and vendors warn that customers who have purchased products based on the 802.11g draft specification (primarily buyers of Apple and Linksys products) have no guarantee that their products won't be obsolete in a few months.

Meanwhile, tests of the so-called Turbo mode of 802.11a have shown that snake oil is still a high-tech industry commodity. Now, even staunch 802.11a backer Intel admits "most commonly, communications takes place at speeds up to 24 Mbps." Market researcher Gartner jumped into the fray in March 2003, warning businesses not to mess with 802.11g, citing "interoperability and performance problems in a multivendor environment, particularly with certified 802.11b products installed in PCs in a mixed 802.11b and 802.11g operating environment."

The 802.11g "Final Draft"

Reports swept the Web in May 2003 that the IEEE had reduced the actual throughput of 802.11g in its latest (and allegedly final) draft. It’s been moved from 54Mbps all the way down to 10-20Mbps (!), crowed the most sensational of the reports. However, this 802.11g transfer rate controversy is meaningless, claims Apple, which has been an early booster of 802.11g. It says the 20Mbps figure quoted in the draft of the standard is the data rate, not the radio rate. In other words, the the data rate has always been around 20Mbit/sec and hasn't changed significantly in the final draft standard. (Yahoo has further details...) The IEEE essentially rubbed-stamped this draft a month later.

Still, each is touted as the successor to the 802.11b technology now commonly used in many unlicensed spectrum (local range) wireless networks. This article details the pros and cons of each new standard.

First, let's look at which companies are backing each specification:

802.11a

Pros:

Faster. No interference with 2.4 GHz devices, due to its use of the 5GHz spectrum. Endorsed as DSRC standard. Backed by Linksys, the #1 vendor in the Wi-Fi market in 2002 and 2003.

Cons:

Shorter range than 802.11g. 802.11a is not compatible with either 802.11b or the 802.11g 54Mbps/sec "standard." Speed drops off sharply as distance increases.

A May 18, 2002 posting by "flatulus" (heh) at Slashdot provides some useful technical information on current implementations. Most notably, the vast majority of current implementations of 802.11a are based on a chipset by Atheros. (Other chipset providers are Resonext and Intersil.)

The 54 Mbit/sec (or 72 Mbit/sec “turbo”) mode of 802.11a is extremely range limited. In a test by CommsDesign, nearly one quarter of a 155x52-foot office with an access point in one corner was outside the 802.11a device's connection area. For comparison, only a tiny area of the same space was unreachable with 802.11g equipment -- and data rates were better in all areas in the connection zone.

This is due to a simple fact of physics: range is proportional to wavelength. At 100 ft, notes flatulus, 802.11a drops back to a speed which is very close to 802.11b. In ideal circumstances, you might achieve connections as far apart as 300 feet. However, in practical use, performance begins to fall off around 60 feet. And, if there's a wall in the way, all bets are off.

802.11a has been endorsed by Dedicated Short Range Communications (DSRC) standards committee as the standard wireless platform for electronic toll payment -- an emerging market expected to gain a very big boost by the auto industry in the very near future.

802.11a employs 152-bit encryption to nominally improve upon 802.11b's notoriously weak WEP (Wired Equivalent Privacy) encryption. However, charge critics, it's still weak.

The inherent insecurity of WEP led Microsoft in April 2003 to offer an alternative to WEP it calls Wi-Fi Protected Access (WPA) as a free upgrade to Windows XP. This introduces the potential for incompatibilities with wireless network users lacking WPA support. Microsoft says Wi-Fi Protected Access also represents a step toward 802.11i, a standard being developed by the Institute of Electrical and Electronics Engineers Inc.'s Standards Working Group for Wireless Local Area Networks. Microsoft has been working with many members of the Wi-Fi Alliance, including Agere Systems Inc., Broadcom Corp., Intel Corp., Intersil Corp., Linksys Group Inc., Proxim Corp. and Texas Instruments Inc., to ensure that Windows XP customers can apply Wi-Fi Protected Access and receive the benefits of enhanced security today, then seamlessly upgrade to 802.11i once it is available. A Microsoft KnowledgeBase article provides the need-to-know details, such as the fact that that each access point and adapter manufacturer must enable WPA in the individual pieces of hardware through firmware updates, and that the update works only with network adapters that support Wireless Zero Configuration (the built-in XP wireless client support) in Windows XP.

The Microsoft scheme, notes Glenn Fleishman at wifinetnews.com, replaces the broken WEP system with the interim 802.11i work, including a robust new key (TKIP), appropriate packet integrity (Michael or MIC, in which the checksum is an integrity check and in the encrypted payload), and adds 802.1x support for network authentication, as well as a consumer pre-shared secret option.

Note also that, although 802.11a is not compatible with either 802.11b or 802.11g, Intel, Agere and other manufacturers offer dual-card base stations which can hold both 802.11a and 802.11b cards, in order to support both standards. (Read more at ZDNet UK....)

Wireless Access Points based on the Altheros chipset include:

• Linksys WAP54A wireless access point

PCI Cards based on Altheros 802.11a chipset:

• Proxim 802.11a Mini PCI card

PC Cards based on Althereos chipset:

• Linksys WPC54A

The current Intel product is limited to 54Mbps/sec rates.

Products such as the two-pound NEC Versa LitePad include 802.11b and 80.11a "combo" adapters, and 802.11a cards are currently selling for under C$100.

802.11g

Pros: Less expensive than some 802.11a offerings. As of Jan. 2003, base stations and cards sell for less than $200 and $100, respectively. Every 802.11g client and AP is capable of falling back and operating exactly like a legacy 802.11b device. Backed by Linksy (the #1 vendor in the Wi-Fi market), Apple and Microsoft.

Cons: Poor range (although better than that of 802.11a), crowded 2.4GHz frequency range makes it ill-suited for crowded RF environments. Slower than 802.11a's "turbo" mode (but faster in most typical environments, or in "Burst Mode"). Products based on "draft" specs may lead to interoperability glitches.

Apple Computer Inc. announced its intent to support the IEEE 802.11g wireless networking standard in Jan. 2003, with its product line dubbed AirPort Extreme. This decision, first hinted at in a June 17, 2002 report at thinksecret.com, is notable for its lack of support for 802.11a.

Apple's initial lineup of "AirePort Extreme" products predated the standard ratified in June 2003. Thus, Apple's implementation  may be subject to change -- and/or possible compatibility issues with IEEE-ratified 802.11g devices. Like 802.11a, it uses OFDM (orthogonal frequency division multiplexing) as its radio transmission technology. A technical description of OFDM is here.

An Apple technical note describes the peak performance range of its 802.11g equipment as 50 feet or less. The Airport Extreme specs say the distance from the base station at which speeds up to 54Mbps are possible is only 50 feet; at 150 feet, the speed drops to 11 Mbps. Comparative tests of 802.11g and 802.11a equipment by CommsDesign found that 802.11g's "range at all data rates was much further than for the 802.11a equipment tested," due to the 2.4GHz signal's longer radio wavelength.

Conclusion

At this writing, enthusiasm for 802.11a appears to be waning ("it stinks" screamed eWEEK in Jan. 2003), but it's still early in the game. 802.11a has the potential to be faster (although, in the above-noted tests, it is actually slower at most ranges, in a single access point environment) and it has less potential for interference -- both compelling advantages in certain applications. There are more channels available in the 5GHz frequency range, making it a more scalable solution for heavily trafficked areas such as highway toll booths and office environments with multiple access points. The 2.4GHz band used by 802.11g and 802.11b has to compete with microwave ovens, cordless phones, Bluetooth-enabled devices, and heaven knows what else around the home. Sure, the ability to fall back to 802.11b-compatible operation is a great feature, but a dual-standard Access Point at the right price could make this a moot point. Intel says it plans to offer an 802.11a/b chip around the middle of 2003. It will follow that with an 802.11z/b/g chip in the second half.

Ultimately, I doubt that either one of the high-speed standards will completely displace 802.11b anytime soon. Intel's 802.11b chipset currently sells to Centrino parts buyers for about US$20. For many applications, 11Mbps is fast enough, and it will almost certainly remain available for the next few years at lower price points than its higher-speed cousins can achieve. With that said, my money's on 802.11g as the standard that deserves to win. 802.11a's limited range is its Achilles' Heel. ::

For Further Reading:

• For more information, see part 2 of our wireless networking feature.
• See also: 802.11b's Dirty Little Secret
• Read more in our Networking Section
• MacBuyersGuide: AirPort Q & A
• eWEEK: Reviews of early 802.11a gear
• CommsDesign: 802.11g Starts Answering WLAN Range Questions
• Small Business Computing: Making the Wireless LAN Choice: 802.11a or 802.11g
• The Register: Don't mess with 802.11g, researcher warns
• ExtremeTech: Intersil Adds "Burst Mode" To 802.11g