Pre-spec 802.11g silicon raises interoperability fears

Broadcom Corp. this week will roll out a two-chip IEEE 802.11g solution for 54-Mbit/second WLANs in the 2.45-GHz 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 — the interoperability and marketing power behind the 802.11 standards — extracted two key .11i functions (802.1x authentication and Temporal Key Integrity Protocol, or TKIP, encryption) 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 roll outs "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.

Issues outstanding

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

According to Bill Carney, director of mark eting for TI's wireless-networking group (Santa Rosa, Calif.), 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 (11 Mbits/s) that doesn't support higher data rates should connect to an 802.11g network running at the full 54 Mbits/s.

"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 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 chip sets 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 conti ngent

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 the second quarter of 2003. "I'd 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 won't announce products until the spec is ratified. We won't know if we can support it properly until that's done. We've seen companies get burned in the past when they've announced something before the specification was complete."

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

"Also, if someone's in the market already, it's 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's 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 doesn't 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's always good for the industry," Ennis said. "If there are non-interoperable implementations, then that's 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 began sampling its two-piece Prism GT 802.11g chip set on Nov. 4 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 this week's Comdex show in Las Vegas to demonstrate an access point based on Intersil's Prism GT chip set and Ubicom's IP2022 processor and software platform.

Both the Broadcom and Intersil chip sets use a 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 quality-of-service (QoS), would enable voice-over-Internet Protocol 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 co nsumer, 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's 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's 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 detaile d 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.