802.11n Fast Wi-Fi Keeps Compatibility Promise


After years of work, the fast Wi-Fi standard is ratified. What impresses Andrew Garcia is the way the industry has met its promises of compatibility

The 802.11n standard for fast Wi-Fi has finally been officially ratified by the IEEE – and the Wi-Fi Alliance has lived up to its promise of certifying products which were designed to meet a draft version of the standard.

When the Wi-Fi Alliance announced earlier this summer that the 802.11n Draft 2.0 certification program would be forward-compatible with the full 802.11n standard upon formal ratification of the latter, wireless LAN implementers finally had concrete assurance that they could move forward with 802.11n deployment plans without fear of any interoperability problems caused by late changes to the standard.

Now, with the 802.11n standard officially ratified by the IEEE, the Wi-Fi Alliance has lived up to its promise by “grandfathering” all Wi-Fi Certified 802.11n Draft 2.0-labeled products to its new certification, called Wi-Fi Certified N, while simultaneously trying to reduce some of the confusion that will arise from the dizzying array of feature configurations that make up 802.11n.

What this means is that hardware manufacturers will  not need to resubmit their products for testing to display the new certification. Instead, companies with Draft 2.0-certified products need only change the certification logo on the packaging and other marketing materials.

Customers who bought enterprise-grade Draft 2.0-certified products from companies like Aerohive, Aruba, BelAir, BlueSocket, Cisco, Enterasys/Siemens, Extreme Networks, Extricom, Intel, Meru, Motorola, Trapeze and Xirrus won’t need to do anything to ensure compliance with the new certification program.

That’s not to say there’s nothing different between the Draft 2.0 certification and the Wi-Fi Certified N certification. For instance, one change that caught my eye was a slightly different approach to Wi-Fi clients – that could make a wider variety of SISO (Single Input Single Output) client devices with lowered power demands eligible for Wi-Fi certification.

Specifically, in the Draft 2.0 testing, access points and clients needed to be able to both transmit and receive at least two spatial streams. While this requirement remains the same in the new program for access points, client devices are now required to transmit and receive only a single spatial stream.

More 802.11n in client devices?

This slight modification could help hasten the delivery of 802.11n radios to certain business-class devices—tablets or netbooks come to mind—that would greatly benefit from a faster WLAN implementation without taking an undue hit on battery performance.

Handheld devices—such as voice over Wi-Fi phones and smartphones—were exempted from this requirement in the Draft 2.0 certification program, but if increasingly optimised SISO radios are developed for other devices, perhaps the price and the power draw will fall to a point where hardware makers can add 802.11n to handhelds with out any drawback.

With Wi-Fi Certified N, the Wi-Fi Alliance also expanded the scope of optional features it will test for as part of the certification process, creating new taglines meant to highlight performance levels over the basic Certified N requirements.

Clearer varieties

For instance, to achieve the new “Dual-Stream N” tagline, hardware makers need to pass tests of optional features like A-MPDU (Aggregated MAC Protocol Data Unit) transmit and STBC (Space-Time Block Coding) transmit, as well as 40MHz channels (but only in the 5GHz band) with at least a 1 (transmit) by 2 (receive) MIMO configuration.

While access points and clients are required to be able to receive A-MPDU aggregated frames (which can be used to reduce the protocol transmission overhead on a wireless network), it is optional that devices be able to transmit these frames (which can be used to reduce the protocol transmission overhead on a wireless network).

A second tagline, called “Multi-Stream N,” highlights even greater performance potential, requiring at least a 3 by 3 MIMO configuration in addition to the requirements needed for “Dual-Stream N.”

In another commendable move, the Wi-Fi Alliance is trying to reduce some of the confusion surrounding dual-band configurations with a new matrix appearing underneath the logo and tagline (if the hardware maker wants it there, of course).

The matrix is designed to spell out what configurations were tested in which band, and provide some information about the nature of the dual-band implementation in question. In this way, buyers may be able to more effectively determine whether a marketed dual-band device has multiple radios or whether a single radio is simply frequency selectable.

Senior Analyst Andrew Garcia can be reached at agarcia@eweek.com.