Wi-Fi Certified 802.11n: Something Old, Something New

By Lisa Phifer

October 02, 2009

The Wi-Fi Alliance promotes all CERTIFIED 802.11n draft 2.0 products to CERTIFIED n while introducing new tests and tag lines to help consumers navigate options.

As promised, the Wi-Fi Alliance announced its Wi-Fi CERTIFIED n test program this week without upsetting the industry's artfully-balanced apple cart. Maintaining 802.11n draft 2.0 requirements as Wi-Fi CERTIFIED n "core technology" made it possible to auto-promote hundreds of previously-tested products, Wi-Fi Alliance executive director Edgar Figueroa told Wi-Fi Planet. As a result, consumers can now rest assured that draft 2.0 investments (including 90% of laptops purchased last year) won't need to be upgraded or replaced with new Wi-Fi CERTIFIED n gear.

Of course, the final standard ratified by the IEEE includes many capabilities not fully-baked two years ago when the draft 2.0 snapshot was taken. Since then, draft 2.0 products have included a dizzying number of option permutations, making it hard for consumers to weed through geek-speak to purchase compatible combos.

To simplify that process, the Alliance also announced a new pair of tag lines—"CERTIFIED dual stream n" and "CERTIFIED multi-stream n"—backed by test programs and detailed matrices. Wi-Fi products—including those auto-promoted to "CERTIFIED n"—cannot wear these new tag lines unless and until they pass corresponding interoperability tests, said Figueroa. This strikes a careful (but perhaps not entirely successful) balance between stability and innovation, complexity and clarity.

Something old: 11n basics

At the top of nearly every Wi-Fi consumer's wish-list is the fond hope that APs purchased from vendor A will plug-and-play with Wi-Fi clients purchased from vendors B through Z. The core requirements tested by the Alliance's CERTIFIED n (nee draft 2.0) program are intended to make that wish come true for every product that wears this spiffy new logo.

Frankly, there's not much new here. With one exception, these core requirements have been present in draft 2.0 products since 2007. Specifically, all CERTIFIED n clients are now required to transmit and receive a minimum of one spatial stream. That's down from the minimum two receive streams required in CERTIFIED draft 2.0 (non-handheld) clients, a change that will make it easier for many more low-power devices to achieve certification (think consumer electronics).

All CERTIFIED n APs are still required to transmit and receive two spatial streams, receive aggregated frames, and confirm frame receipt using a shorter, more efficient block ACK. And APs and clients are still free to operate in either the 2.4 or 5 GHz band (or both, selectively or concurrently). Omitting this essential detail from the new logo is likely to confuse some end-users, but hopefully most vendors will clearly identify band support on product packaging—preferably using the new Alliance-specified option matrix.

To help consumers understand the benefits of replacing now-ancient Wi-Fi CERTIFIED a, b, or g gear, the Wi-Fi Alliance also launched a new education portal. www.11nbasics.org does a better job of concisely explaining what to expect from Wi-Fi CERTIFIED n products in (mostly) layman's terms. Brief videos and a white paper highlight 802.11n's improved reach and reliability, increased speed and capacity, but the biggest message is backwards compatibility, delivering that hoped-for "warm fuzzy." New taglines receive only brief mention here, using an easily-grasped highway analogy to explain why bandwidth-sucking apps and multi-user households might benefit from extra lanes (i.e., spatial streams).

Something (sort of) new: dual and multi-stream

End-user eyes might glaze over when talk turns to MIMO and A-MPDU, but enterprise admins know that this is where important product differences lie. Thus, the most significant and potentially-contentious part of this week's Wi-Fi Alliance announcement are the option bundles that constitute CERTIFIED dual-stream n and CERTIFIED multi-stream n.

According to Figueroa, the Wi-Fi Alliance took a hard look at how optional 802.11n capabilities tend to be implemented in concert and the usage cases they can support. Rather than leaving the "more-than-core" market wide open to dozens of permutations, the Alliance carved out two option bundles they believe many vendors will implement and consumers will find useful.80211n.jpg

Dual-stream n ups the ante to a level where both clients and APs must receive at least two spatial streams and send aggregated frames, doubling max data rates from 150 Mbps (core) to 300 Mbps (dual-stream) for WLANs that need high throughput and/or capacity. While dual-stream n products in the 5 GHz band must support 40 MHz wide channels, 2.4 GHz-only dual-stream n products must now default to 20 MHz channels—an anticipated choice that sacrifices throughput in favor of coexistence. In addition, dual-stream n APs must now support transmit space time block coding (STBC), a signal processing technique which sends redundant data differently over two spatial streams to improve error recovery in products that have "extra" transmit antennas. Many of today's draft 2.0 products already implement this option bundle—now they'll be required to pass new tests to promote interoperability.

Multi-stream n raises the bar another notch, reaching the 450 Mbps max data rate increasingly common in enterprise WLAN gear. Here, both clients and APs must transmit and receive at least three spatial streams—and leaving room for future products can optionally support a fourth. Spatial stream permutations are the only difference between multi-stream and dual-stream n. In fact, both multi-stream and dual-stream n give clients more latitude in transmit/receive combos—a reflection of product diversity as Wi-Fi clients are embedded in a broader range of devices. But lumping several permutations under a single tag line leaves purchasers reading fine print. To simplify selection without resorting to 6-12 different tag lines, the Alliance introduced an optional matrix that clearly identifies band support and tested transmit/receive spatial streams.

Toeing the line—or choosing not to

Manufacturers are not required to pass certification tests associated with these new tag lines. In fact, many Wi-Fi CERTIFIED n products will support options without wearing these tag lines. However, any product that undergoes CERTIFIED n testing is now required to pass new tests for all implemented options, with results detailed in per-product certificates published by the Wi-Fi Alliance.

This change affects not just new products, but existing products that undergo revision (as many auto-promoted products will do soon anyway for routine maintenance). The consequence should be gradual improvement in multi-vendor interoperability for capabilities not previously tested. Those include the afore-mentioned STBC, A-MPDU, and three-stream capabilities, along with a new test for 20/40 MHz co-existence (i.e., interference avoidance) applied to all CERTIFIED n products using the 2.4 GHz band.

Naturally, manufacturers are free to include other options defined by the standard or that go beyond the standard without impeding interoperability. Those optional untested features include transmit beamforming—already implemented in some enterprise-class APs, but not uniformly embraced by all manufacturers. The number of channels supported by CERTIFIED n products using 5 GHz will also continue to vary, reflecting not just regulatory domain, but indoor/outdoor/product-specific differences.

This Wi-Fi CERTIFIED n test program employs reference platforms from Atheros, Broadcom, Intel, Marvell, and Ralink—the first seven devices eligible to wear the new logos. For example, Ralink products are being used for 1x1 (150 Mbps), 2x2 (300 Mbps) and 3x3 (450 Mbps) tests, and to capture and analyze wireless traffic for debugging during certification tests. Tests are now being conducted at just two labs, including TÜVRheinland, but additional test labs are expected to come on-line soon to support the anticipated heavy/global workload as manufacturers—especially those with enterprise-class products—scramble to achieve tag line certification.

Balancing stability vs. innovation and complexity vs. clarity is tricky business. With this announcement, the Wi-Fi Alliance reassured nervous consumers, reduced option confusion, and raised the bar on future/advanced interoperability. Except for band support, differences important to retail consumers are reflected in the new logo and tag lines. Enterprises must drill into optional matrices and test certificates to get the details they need, but can now compare apples-to-apples more easily. And manufacturers still have room to grow and innovate. These are all big steps in the right direction—only time will tell if they're completely successful.

Lisa Phifer owns Core Competence, a consulting firm focused on business use of emerging network and security technologies. A 28-year networking industry veteran, Lisa has been involved in the design, implementation, and testing of wireless products and services since 1996.



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