* There’s 802.11n, and then there’s 802.11n
A reader recently pinged me with an observation and a question about forthcoming 802.11n products. He pointed out that over the years, the wireless LAN industry has used the terms “802.11a,” “802.11b” and “802.11g” to uniquely identify a combination of RF spectrum and a modulation technology. Enter 802.11n, which – unlike any of its predecessors – is capable of operating in both the 2.4GHz and 5GHz bands. He wondered if we need more specific terms now to identify products. Indeed, the term “802.11n” by itself doesn’t define all the variables of a given solution. How do you know if a given vendor’s solution operates in one or both bands? And if it operates in just one band, which band is it?
This piece of information could affect interoperability. There are single-radio access points and clients shipping today that are based on the Draft 2.0 IEEE 802.11n standard. Obviously, a client operating solely in one band can’t talk to an AP operating solely in another band.
According to the draft IEEE standards for 802.11n, the technology is mandated to be backward compatible with 802.11a/b/g networks. But this rule can be misleading. 802.11b and 11g operate in 2.4GHz, while 802.11a operates in 5GHz. It’s impossible for a single radio to operate in both, so to accommodate all the legacy WLANs, forthcoming APs and clients would have to have dual 2.4GHz/5GHz radios.
For clarification, I turned to Bill McFarland, CTO at Atheros, maker of Wi-Fi chips used in nearly all enterprise-class WLAN products today. Here’s his interpretation of 802.11n interoperability requirements in the latest draft under consideration, Draft 3.0:
“802.11n products may work in either the 2.4GHz band, the 5GHz band, or both,” he said in an e-mail. And, according to the standard:
* Any 802.11n product that works in the 2.4GHz band will be compatible with 802.11g devices.
* Any 802.11n product that works in the 5GHz band will be compatible with 802.11a devices.
* Any dual-band 802.11n product (one that can work in either band) is compatible with both 802.11g and 802.11a devices.
The lesson? Make sure the frequency bands match up on the products you buy.
