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Pre-spec 802.11g silicon raises interoperability fears

Posted: 20 Nov 2002 ?? ?Print Version ?Bookmark and Share

Keywords:wlan? ieee 802.11g solution? chipset?

Chipset vendors are moving headlong into IEEE 802.11g WLAN silicon before the ink is dry on the standard, hoisting the specter of non-interoperable 802.11g solutions in a market that has depended on interoperability for its very success.

The preemptive strikes have raised eyebrows among some observers, who are calling for restraint even as they acknowledge the market's jackhammer competitive pressures.

Broadcom Corp. will soon out a two-chip IEEE 802.11g solution for 54Mbps WLANs in the 2.45GHz band that Linksys Group Inc. will put on store shelves by early December. The company joins Intersil Corp. and Texas Instruments Inc. in announcing silicon support in advance of the standard.

That all three silicon vendors have felt the need to announce prematurely reflects both the success and the pull of the WLAN market. It also reflects the snail's pace of the IEEE standards process, which can take years to implement extensions.

While the much-anticipated .11i security and .11e quality-of-service components are said to be close to ratification, even those extensions have been pilfered in advance. Recently the Wi-Fi Alliance - interoperability and marketing power behind the 802.11 standards - extracted two key .11i functions and repackaged them as the Wi-Fi Protected Access scheme in a bid to address many of the security concerns that have slowed WLAN penetration, particularly to the enterprise.

The uncoordinated introduction of 802.11g chips has drawn some criticism. "My perspective is that (the vendors) should have exercised a bit of patience," said a systems engineer who asked not to be identified. But in a nod to the market's cut-throat environment, the engineer conceded that "people will do what they need to do."

The early rollouts "could be a problem," said Allen Nogee, an analyst with In-Stat/MDR. "No one wants to be non-compliant. The good thing is that most of these offerings are flexible enough to be upgraded when the standard is finished."

To address non-compliance concerns, Broadcom has announced an interoperability effort that it hopes will attract other semiconductor manufacturers and OEMs to eliminate the possibility of a fractured market. "I anticipate that other companies will participate. The suite of tests will be a stopgap measure before the Wi-Fi Alliance (acts), but we expect the industry as a whole will have a mechanism now for interoperability," said Jeff Abramowitz, senior director of marketing at Broadcom.

Outstanding issues

The 802.11g draft standard is expected to be ratified next May. An IEEE meeting in Hawaii focused on resolving more than 190 comments on the latest draft ballot.

According to Bill Carney, director of marketing for TI's wireless-networking group, most of those comments revolved around the short-time-slot option. Introduced two meetings ago in Vancouver, that option determines how an older 802.11b node that does not support higher data rates should connect to an 802.11g network running at the full 54Mbps.

"The question then becomes, "How do you throttle back the .11b device to have some guaranteed bandwidth and to interoperate?" There are lots of technical responses as to how it should be done," Carney said.

Even if the standard is completed by May, it will be another three to four months before Wi-Fi certification can begin, said Brian Grimm, marketing director of the Wi-Fi Alliance. "We need two chipsets and four implementations before we can even start," he said.

According to Greg Ennis, technical director for the alliance, the group is gearing up now to begin certification next month of dual-band .11a/b solutions.

Conservative chip contingent

Some chip vendors, meanwhile, are willing to wait for all the pieces to fall into place before making announcements.

Agere Systems Inc. and Infineon Technologies AG recently announced a partnership to develop a combo solution for .11a/b/g by Q2 of 2003. "I would worry about being prestandard," said Tony Grewe, director of strategic marketing at Agere, "especially from a system reliability standpoint." Agere will wait until after the standard is ratified and will then push hard in the latter half of the year, with plans to ship product in quantity in early 2004.

Maureen Smith, WLAN marketing manager at WLAN integrator Proxim Corp., which emphasizes the enterprise market, said her company has ".11g on the road map but will not announce products until the spec is ratified. We will not know if we can support it properly until that is done. We have seen companies get burned in the past when they have announced something before the specification was complete."

But Broadcom, TI and Intersil maintain that their architectures are sufficiently flexible to be modified, if necessary, for interoperability.

"Also, if someone is in the market already, it is easy to follow the leader and make sure they're interoperable," said Broadcom's Abramowitz. "The same thing happened with .11a and TKIP."

Broadcom nonetheless is hedging its bets by floating its 802.11g interoperability effort and inviting others to join. But TI's Carney said he would "question having an effort outside the Wi-Fi Alliance, as that is really where brand approval needs to be done. The problem with such a plugfest is that they could end up being different than what the alliance ends up doing. Early interoperability does not necessarily imply later interoperability."

The Wi-Fi Alliance, for its part, is staying neutral on the subject. "We always want to keep this clear: To the extent that there are activities that promote interoperability, that is always good for the industry," Ennis said. "If there are non-interoperable implementations, then that is going to cause confusion."

Broadcom's offering is sampling now, with volume shipments slated for December. The company is banking on the very tightly constrained nature of the .11g spec to ensure a high degree of interoperability out of the box, even before testing begins. "No chip vendors are shipping product, so we can't test with them yet," Abramowitz said.

But Intersil marketing director Ron Paciello demurred. Intersil has begun sampling its two-piece Prism GT 802.11g chipset and has been involved in design efforts with such companies as Accton Technology, Actiontec, Ambit Microsystems, BroMax Communications, and Z-Com, he said. In fact, Ubicom will use the Comdex show in Las Vegas to demonstrate an access point based on Intersil's Prism GT chipset and Ubicom's IP2022 processor and software platform.

Both the Broadcom and Intersil chipsets use direct-conversion architecture. Broadcom emphasizes its use of CMOS from input to output, although it does use an external silicon germanium power amplifier.

TI's offering, the TNETW1130, is a baseband/MAC-only solution, although it caters to all four WLAN versions, both standard and non-standard: a, b, b+ (TI's proprietary PBCC-based technology) and g. According to Carney, TI will partner with an RF vendor for the complete solution. The TNETW1130 will ship in early 2003.

While 802.11g looks to be on time for May, another, highly anticipated extension of the 802.11 MAC is also nearing completion. Extension .11e, which caters to QoS, would enable VoIP, and multimedia-streaming applications.

The QoS discussion "has been going on for about three years," said TI's Carney, with diametrically opposed camps having each implemented their own versions: the Enhanced Distributed Coordination Function (EDCF), backed by enterprise, voice and data proponents; and the Hybrid Coordination Function (HCF), backed by consumer, home electronics and audiovisual proponents.

EDCF leaves it up to the network to decide priority, using statistical algorithms. HCF is more of a pullback method whereby particular clients can be provisioned to have a guaranteed data rate or priority. "HCF is much more intelligent and hierarchical," said Carney, "and it is deterministic. EDCF enhances current mechanisms for the distributed management of bandwidth."

In the end, Carney sees the .11e Working Group making the two approaches optional, which he believes will fissure the marketplace. But "both camps are far down the road on implementation, so it is the only sane resolution right now. Ours (the TNETW1130) supports both." He expects the draft to be ready by the May or July meeting.

New extension proposals

The work being done on QoS stands to benefit from another standard proposal. Tentatively labeled 802.11k, the proposal comes from the resources management group and would allow the gathering of detailed information about the communications link between stations and clients. That information would then be conveyed back into the network for use by administrators and operators.

"So, if an operator had all the qualitative information about a station in a home and its performance capabilities, it could then know how to provision it downstream, etc.," said Carney. "Laid on top of QoS, it will strengthen (802.11e)."

- Patrick Mannion

EE Times





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