- Image by » Zitona « via Flickr
editor’s note: Feel free to groan about the title, @joelvincent came up with it 
With 802.11n ratification upon us, a number of people are wondering what the differences are between Draft 2.0 of 802.11n and the final standard. Draft 2.0, as most of you know, is the basis for the Wi-Fi Alliance certification for 802.11n, which has been available for two years now. 802.11n has gone through nine more drafts since that time.
The good news is that not much has changed, when it comes to features. In fact, for the features of 802.11n that make up the basis of Wi-Fi Alliance certification, so little has changed that the Wi-Fi Alliance has announced that they have not had to change their base testcases and will let 802.11n Draft 2.0 certifications automatically convert into certifications against the final standard.
But, clearly, something had to have changed from Draft 2.0 to the standard. Most of the changes were to the language of the standard–the way the features were described–rather than to the operation of the features themselves. So 40MHz transmissions are still 40MHz transmissions, multiple spatial streams operate the same way in the standard as in Draft 2.0, and all of the features that make 802.11n reach 200Mbps goodput in enterprise applications remain the same. Some of the uncommon 802.11n features–all standards are a mixture of features that become commonplace and mandatory and a set that are optional and rarely implemented–did get added or changed, and the precise way devices that cannot handle 40MHz transmissions can agree on the channel width have been clarified. But, overall, it’s the same 11n that has been here for the last two years, just better written.
