Here I am trying to digest all the latest reports and angles after the vote in Denver last week elevating 802.11n to Draft 1.0 status. Near as I can tell, it boils down to issues surrounding the practice of combining two 20 MHz 802.11 channels, one of the techniques besides MIMO to boost throughput.
Airgo, the odd man out in the n wars, appears to be the most vocal. You’d think Atheros would speak up too. After all, their first generation two-channel turbo mode using channels 5+6, caused so much consternation with existing deployments that the default mode was switched to single channel. All of a sudden turbo was about as useful as a flat tire.
Never-the-less, all basically agree that there needs to be a good way for 802.11n to become a good neighbor with the millions of 802.11 b/g units already out there. Apparently the draft is not completely clear about this – detecting neighboring channel usage, what to do about it (back off to one channel, use non-adjacent dual channels, etc.), what’s mandatory and what’s optional, and so on.
Fast forward to the 3rd Generation Airgo chipset that claims to be neighbor friendly. Not so, according to this review at Tom’s Networking, and I find that rather curious.
So who does have the solution? This problem is not new. For instance, to this day, 802.11g devices running in a mixed b/g environment with active b devices gain very little performance unless all b devices are quiet.
This is hard to comprehend, but think of it this way: An 802.11g device gets a slot to send a packet and transmits faster (54 Mbps raw best case) than 802.11b. So far so good. But then b gets a turn, and transmits some 5x slower (11 Mbps raw) than g. That robs time away from g when it could have sent five packets in the same amount of time.
We will see the same problem with n in the Enterprise. Until the environment is mostly free of b/g devices, there may be little gain in performance.
Maybe this will help spur migration to the 5 GHz band where there are more channels with less interference. In the enterprise, this would be the ideal home for 802.11n. For consumers, it probably doesn’t matter unless you’re concerned about getting along with your neighbors. Literally.