Carrier WiFi

Interop Woes Smite 802.11g

Like any standard, the 802.11g wireless LAN standard is supposed to deliver on the promise of seamless interoperabilty by ensuring that compliant equipment from different manufacturers will work together. Now, in an ironic twist, some vendors are claiming it could actually cause those interoperability problems [ed.note: well ain't that a kick in the dentition?].

It's an issue that could have serious ramifications for the development of the nascent 802.11g market. And it's also one that has caused a war of words to break out among vendors, who can't even agree on whether a problem exists -- let alone how serious it is.

Fueling industry anxiety is the fact that the results of the first interoperability trials, sponsored by the University of New Hampshire Interoperability Lab, won't be made public -- causing some to cry "vendor whitewash."

In the meantime, at least one major 802.11 player is holding off shipments of 802.11g until the problems are resolved. "There have definitely been some issues and until these issues are resolved and 'g' is ready for prime time, we're not going to ship it," says Brice Clark, worldwide director, strategy and business planning for Hewlett-Packard Co.'s (NYSE: HPQ) ProCurve networking business.

There are actually two concerns about 802.11g. Concern No. 1 is whether the technology will work with legacy 802.11b clients; the big fear is that legacy 802.11b clients could be knocked off the air in favor of 802.11g kit in crowded networks. Concern No. 2: whether all 802.11g products will be able to interoperate, particularly with the number of pre-standard products being announced.

The stink of incompatibility would be bad news for the emerging "g" standard, since there is already a large installed user base for 802.11b. Around $2.2 billion worth of 802.11b kit was sold in 2002, according to In-Stat/MDR. Potential customers for wireless networking equipment are unlikely to adopt 802.11g if it interferes with the smooth running of the 802.11b wireless networks they already have in place.

Broadcom Corp. (Nasdaq: BRCM) officials, who claim they've shipped nearly 1 million 802.11g chips already, dismiss these stories as scare tactics from the opposition. "We saw some rumors in Taiwan and some rumors in the investment community -- which our CEO squashed" during last week's earnings conference call, says Jeff Abramowitz, senior director of wireless LAN marketing for Broadcom (see Big Day at Broadcom).

So what's true, and what's false? Vendors will get their first real taste this week, in a group test sponsored by the U. of N.H. Interoperability Lab.

The results could be "a little bit messy," says Sheung Li, product line manager for chipmaker Atheros Communications.

Unfortunately, Joe Consumer won't be made privy to the data, because this week's UNH tests will be kept under wraps for a year, under a non-disclosure agreement, designed to allowed vendors to sort out their glitches without having to admit to problems.

Under the auspices of the Institute of Electrical and Electronics Engineers Inc. (IEEE), 802.11g is a wireless LAN standard aimed at bringing the 54-Mbit/s speed of 802.11a into the 2.4GHz radio band used by 802.11b. The common radio band is supposed to allow 802.11b clients to surf new 802.11g networks without a problem, although they'll still be limited to the 11 Mbit/s of the 802.11b standard.

But will "b" clients find themselves B-listed on future networks?

1. The shutout
That's one concern: that 802.11b users could get frozen out of the network because of contention with 802.11g clients. According to Li, this is possible because the standard stacks the deck in favor of 802.11g.

"When a 'g' and a 'b' fight for air time, the 'g' will always win," Li says.

Ideally, that wouldn't be a problem for 802.11b users, because there's a protection mechanism written into the 802.11g standard. But Li claims some equipment vendors are ignoring this.

"That's the cause of some of the interoperability problems," he says. "One way you can boost your performance is to not send out the protection mechanisms."

Li's point is that the protection mechanism is bulky. For high speeds, 802.11g uses orthogonal frequency-division multiplexing (OFDM), just as 802.11a does. But the protection signal has to be receivable by 802.11b clients, meaning it must be sent using their complementary code keying (CCK) waveform. Because the CCK preamble -- the initial string of data starting a transmission -- is longer than OFDM's, the protection message can damage network performance noticeably.

Without the protection mechanism, an 802.11b card wouldn't realize that there's an 802.11g traffic stream in its way. It would send continual attempts, receive no answer from the network, and assume that the access point is down. In effect, the user would think the network has crashed.

But Broadcom's Abramowitz says none of this is an issue, because it's not true that 802.11g takes priority over 802.11b.

"There is no priority for 'g' over 'b,' not to my understanding," he says. "The spec is designed to be fair." Even without the protection mechanism, 802.11g and 802.11b feeds would simply share the bandwidth -- one wouldn't walk over the other, he says.

2. Preambles
Then there's the matter of those preambles. Because 802.11g incorporates 802.11a and 802.11b transmission methods, vendors face two options for the preamble signal, the initial string of a data transmission.

Radios using one preamble won't talk with radios using the other preamble. And that opens up the possibility that two makers' 802.11g equipment won't be able to talk, according to Bruce Sanguinetti, CEO of chipmaker Bermai Inc.

Sanguinetti considers this a major trouble spot. In December, he told the audience at 802.11 Planet that companies were "irresponsible" in releasing pre-standard 802.11g products without completing interoperability tests first. "They need to be interoperable before they launch," he told Unstrung.

Broadcom's Abramowitz acknowledged that a "short" and "long" preamble coexist in the current 802.11g draft, but he wasn't convinced that the two were incompatible. Even if a problem is possible, it's "not a spec issue -- it's more of an implementation issue," he says.

3. Revisions
Finally, there's the issue of the evolving 802.11g standard. Li is concerned that versions 4, 5, and 6 of the spec won't work together due to differences in control messaging and signal timing. That's why he's worried the plugfest could get "messy" and why he believes it's too soon for vendors to announce 802.11g equipment.

"It says on Page 1 [of the 802.11 draft spec], 'These are working drafts. Do not build product.' Page 1," he says.

Broadcom's Abramowitz brushes off this concern. For starters, he says, it's moot: "The only products that are out on the shelves are based on Broadcom technology, and that's [802.11g draft version] 5.1."

Moreover, versions 4, 5 and 6, including the current 6.1 draft, are "not incompatible by any stretch," Abramowitz says. "We can tell you that 5.1 products and 6.1 products will work together all the way up to 54 Mbit/s." He adds that all the version 5.1 chips can be upgraded to version 6.1 through firmware -- installing a new device driver, essentially.

The common thread among these different concerns is the fear that equipment providers could endanger things by being careless. Even if the 802.11g spec covers all possible pitfalls, shortcuts in access-point architectures could disrupt interoperability.

But Abramowitz is convinced equipment makers won't let that happen. "They understand what interoperability means to them, and they are moving in that direction," he says.

— Craig Matsumoto, Senior Editor, Light Reading, and Dan Jones, Senior Editor, Unstrung

Steve Saunders 12/5/2012 | 12:47:02 AM
re: Interop Woes Smite 802.11g this is all ever so reminiscent of the good old bad old days of wired Ethernet standards, isn't it?

joset01 12/5/2012 | 12:46:21 AM
re: Interop Woes Smite 802.11g Tim Higgins, managing editor of SmallNetBuilder, wrote in to tell us about his experiences with 802.11g interoperability:

"Re: "Interop Woes Smite 802.11g", my testing of Linksys' WAP54g and WPC54G show the opposite of what you assert, i.e. that 11b loses to 11g. The Chariot test plots on page 3 of the review show that the 11g client virtually grinds to a halt when an 11b client starts using the network. http://www.smallnetbuilder.com... These findings were confirmed by Linksys, who said they were due to the "newer firmware" (newer than used by Buffalo Technology) they used."

The plot thickens, eh, readers? Anyone else have real world experience of using 802.11b and 802.11b systems together?

We'd love to hear from you...

DJ Unstrung
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