The IEEE has begun accepting comments on the just-adopted 802.11n draft standard for 100-plus Mbit/s wireless LANs. The number and scope of the responses will determine whether there will be big or small changes to the draft at the next 802.11n task group meeting in May.

Small changes will keep the standard on track for final ratification and interoperability testing in mid-to-late 2007. Long before then, vendors hope the standard will be firmly set enough to provide a base for the next generation of WLAN products.

Network professionals seem to be in no hurry.

"[802.11n] would require a hardware forklift for most folks, including us, where we seem to be able to deliver adequate performance for real-time services, or other bandwidth consumers, with 802.11g/a," says Brad Noblet, COO for Harvard University's faculty of arts and sciences.

That will remain true for about two years, says Bob Egan, director of emergent technologies at consulting firm Tower Group. "I don't think there's a compelling reason to do a wholesale swap-out because 11n has a faster access method," he says.

But if you want to see the next generation, there will be a selection of products in just a few months. By June, several vendors say they expect to introduce pre-N, or draft N, products based on new chipsets from Atheros and Broadcom.

Netgear promises data rates of up to 600 Mbit/s for its new line of products, based on the draft standard, to be launched by June. The new designs were showcased at the recent Cebit show in Germany. Linksys, the consumer division of Cisco, says it will launch draft 802.11n products in the second quarter. "We're confident they will be software upgradeable [to the final 11n standard] but we haven't said we'll guarantee that," a spokeswoman says.

A technology called Multiple Inupt Mulitple Output (MIMO) creates multiple datastreams between two or more antennas on both sides of the radio link to boost throughput far beyond the 22 to 24 Mbit/s possible with today's 802.11g and 802.11a networks. The first commercial MIMO chipset, by Airgo Networks, was brought to market in 2004. Belkin was among the first to launch an Airgo-based access point and adapter cards, rated at faster than 108 Mbit/s, in October 2004.

While rivals such as Atheros and Broadcom are just now bringing out their first generation of MIMO in the draft 11n products, Airgo executives say they are focused on a fourth-generation chip designed to fully implement the final 11n standard.

There's more to it than speed
But enterprise customers with some WLAN experience are not swayed by the promise of a huge boost in throughput. Other issues are critical.

"I have serious doubts about 802.11n's usefulness and effectiveness in a largely uncontrolled, shared, roaming airspace such as a college campus," says John Bucek, executive director of IT at Mount Saint Mary College in Newburgh, N.Y. The college has a campus-wide 802.11a network. "I would have to see some test results using 802.11n in a multiple access-point environment before I would buy any product for evaluation. All of the pre-n tests that I have seen show reasonable performance and range improvements, but they only involve one access point. That may be fine for home or small-business use but not for a campus network."

Bucek says even in home use, the current crop of MIMO-based products "appear to be non-friendly to neighboring 802.11b/g products."

As it voted to accept the draft document, the 11n Task Group created an ad hoc subcommittee to tackle that problem. The subcommittee was spawned out of a contentious battle that erupted at the last meeting.

The 802.11n radios will be able to run in 20MHz and 40MHz channels, the larger channels providing more throughput. But using wider channels in the 2.4GHz frequency can clobber 802.11b/g devices, which run in 20MHz channels. The ad hoc group has to figure out whether to recommend one or several mechanisms to avoid this problem, and whether to make them mandatory or optional.

Despite enterprise skepticism, analysts predict a ready market for even the draft 802.11n products. These will make up about 15 percent of all home WLAN products shipped worldwide this year, according to Dell'Oro Group. The research company forecasts that by 2009 11n gear will have reached 90 percent of consumer WLAN shipments.

Enterprise buyers will be slower to adopt, Dell'Oro says, but large-scale enterprise deployments will pick up speed throughout 2008 and 2009.

"No one [in the enterprise] should be delaying purchase of existing WLAN equipment," says Craig Mathias, principal with Farpoint Group. With 802.11n certain to be compatible with 802.11b/g and probably 802.11a client devices, network groups can phase in 11n products as part of their periodic three- to five-year refreshment of WLAN infrastructure, he says.

The new standard will have little impact on network design or infrastructure, Mathias predicts. Although 802.11n will reach further than today's WLANs, Mathias still recommends deploying access points densely, to sustain large numbers of users,and high throughput.

Planning and design for 802.11n deployment requires the same analysis as for existing WLANs, he says: Clearly identify who the users are, what applications they're using, the number of channels needed and whether voice traffic will be added in the future.