Will 802.11b Work with 802.11g?
January 31, 2003
Some say that in the rush to reach customers first, early 802.11g gear may leave interoperability with current 802.11b devices in the dust. Equipment manufacturers say no, but have secretly gathered to test for incompatibility under the auspices of the Wi-Fi Alliance.
Even before the standard for 54Mbps 802.11g is finalized, vendors aware of the growing interest in 11g have been announcing and shipping products based on the technology, hoping to lay claim to part of a lucrative Wi-Fi market. But in the rush to be first to reach customers, is early 802.11g gear leaving the all important interoperability with 802.11b devices in the dust?
As microchip executives defend their decision to market products based on the unratified 802.11g specification, technicians gathered at the University of New Hampshire to conclude the latest round of closed-door tests of 802.11g products heading for a store near you.
Rush to Market?
"The problem with some of the early (11g) chips, is there was a rush to market to have something labeled G-ish," says Rich Redelfs, CEO of Atheros. He made the comment at a press conference announcing that four major laptop makers will use Atheros' 11a/b and 11a/b/g chips.
The new debate over 11g calls into question one of prime attractions of the technology: the 54Mbps wireless networking standard's backward compatibility with the slower 11Mbps, but more widely-available, 802.11b. Both use the crowded 2.4GHz radio frequency band.
The 802.11g standard uses orthogonal frequency-division (OFDM) to attain its high data speed. To protect 802.11b users, 802.11g is required to also send a protection signal based on the longer complementary code keying (CCK.) In interviews earlier this week, Sheung Li, an Atheros product line manager claims some vendors are bypassing the protection signal. Omitting the protection signal ensures high data speeds for 11g users, at the cost of locking out 802.11b users.
Without the protection, an 802.11b user would be blocked by an invisible flow of 802.11g data and assume the wireless network had crashed.
"The IEEE decided to prioritize G over B in a mixed environment," says Redelfs. "The decision was that if you got G, you want the speed, so they come first," he says. "B gets low priority to the air," according to the Atheros CEO.
"We don't share this perspective," says Jim Zyren, director of strategic
marketing at Intersil
. "Our testing has not shown
this effect," says Zyren. Intersil's 802.11g chip, the PRISM GT is used
by D-Link and Netgear, among others, says Zyren.
Zyren says the latest draft version of 11g gives two times as much access than 11b, but "every 11g device must be able to communicate with 11b." Zyren says Intersil will support the protection signal mechanism. The chipmaker representative says the concerns are the result of "technical misinterpretation" or misconfigured access points.
, which powers many 11g products
available now including those from Buffalo
Technology, calls stories of 11g interoperability problems "scuttlebutt"
and "rumors." Chips produced by Broadcom will use protection mechanisms
ensuring 802.11b compatibility, although the protection signal portion is "now
only partially implemented," says Mike Hurlston, Broadcom's director of
Hurlston says when the final 802.11g standard is approved, the optional protection mechanism will be mandatory and "if 11b is present, protection must be used."
He does admit there is a problem with an incompatibility between 11g and so-called "legacy" 802.11b cards. The problem is older 802.11b cards will not be able to join 11g networks due to an incompatible number of data rates. While 11g devices recognize 12 different rates of speed, 11b sees only eight.
"If 802.11b devices get more than eight rates, they don't know what to do," says Hurlston. The problem was answered by the IEEE deciding to divide the 12 rates into a block of eight and another segment of four rates. Hurston said older 802.11b devices could be updated by a software fix.
Redelf says there are just too many versions of 802.11g floating around and with the different versions come confusion and questions of interoperability not just between 802.11g and 11b, but also between various versions of 11g.
"I don't want to taint the market against 11g," says Redelf, but "people have just jumped the gun." Redelfs denied Atheros is a lone voice, citing previous reports of 11g's failings.
Equipment Vendors SpeakWhat do equipment vendors say about this war of words? Morikazu Sano, Buffalo Technology's vice president of networking, has no concerns about Broadcom's chip.
"We worked with our chipset manufacturer, and together worked through any 802.11b interoperability or compatibility issues related to Buffalo's pre-standard 802.11g products."
Joseph Moran, a contributing editor and product tester for 802.11 Planet, who has reviewed Buffalo's AirStation G54 Broadband Router Access Point, says "you get the sense that they're releasing the firmware du jour on a fairly regular basis, to include various interoperability and performance tweaks in anticipation of the final 802.11g standard."
Moran says he was able to get a D-Link 802.11b card to operate with Buffalo's access point, using the product's dual b/g mode. The product has a G only mode that will not work with B cards.
says it will wait until the 802.11g
standard is finalized later this year before releasing an 11g version of its
"HP generally likes to wait until standards are together," says an HP spokesperson.
So, are these concerns signs of real problems for 802.11g, or is it all smoke?
Is There A Fire?
"It's mostly smoke," believes John Chang, senior analyst for the Allied Business Intelligence research firm. Chang says while 11g is not ratified, "the vendors have worked closely with the IEEE to make sure that there were no surprises with the full 11g standards."
"Certainly the G spec does have a void in spelling out the way that G and B nodes interact," says Allen Nogee, analyst with the In-Stat/MDR research firm. Nogee says makers of 11g-based gear are working on the gaps and 100 percent compatibility won't be likely until the Wi-Fi Alliance begins testing pre-standard gadgets.
Nogee says the same concerns about interoperability surrounded 802.11b at first.
When manufacturers added 128-bit Wired Equivalent Protection (WEP)
The analyst says 802.11g will be the same. "If you are not willing to deal with the problems, I don't recommend that you buy a card six months before the standard is even approved."
If industry insiders aren't certain if current 11g products suffer from a lack of compatibility, how is the buying public to make intelligent purchasing decisions? Testing is one answer.
Chipmakers and equipment vendors gathered this week at the University of New Hampshire's Interoperability Laboratory to conduct secret tests of 802.11g and 802.11b compatibility. Participants were required to sign a strict gag order, or non-disclosure agreement, by the Wi-Fi Alliance industry group. The gag order keeps the results of the tests out of the public eye for a year, after the Alliance can put its own stamp of approval on 802.11g products sometime in May or June, after the specification is ratified by the IEEE.
Dennis Eaton, chairman of the Wi-Fi Alliance, says the secrecy is needed to attract companies to the private tests. Eaton says he "expects some interoperability issues" to arise during tests of the products and if the results were published, "some vendors might choose not to attend."
The Univ. of New Hampshire 11g interoperability test was the fourth in a series of events the Alliance is using to create a test bed of data it can use during the later certification process. The Alliance has already certified 11b products and recently began certifying 11a devices.
Does 11g have a serious interoperability problem? Equipment manufacturers say no, yet secretly gather to test for such incompatibility. Analysts provide a mixed message of assurance and warning. As more 11g products make their way to the market, customers at home and in offices will be the last to learn the real answer.