I have run some rate control experiments in a semi-quiet environment
(two ath cards and no other 802.11 within at least 100m and probably
300m or more).

With onoe, it's clearly buggy.  the rate drops from 11 to 5 (5.5
really) due to errors (when I induce them), but then doesn't drop
further; it keeps setting -1 and then claiming 11->5.5.  Output really
seems to be at 5.5.  With low retries, it doesn't go back to 11.

The logic to drop rate seems perhaps off, unless it assumes (and it's
correct) that failed packets report retries at the same time.  In my
opinion, if the # of failed packets is significant compared to those
that make it, backing off is in order (unless one finds that factors
other than rate cause loss, and track the performance of various
rates, and respond quickly to changes caused by motion).

All that said, the basic scheme seems reasonable if not optimal.

With sample, I see a return to high rate when warranted.  But, it
seems to endure a huge number of failed transmissions without backing
off in rate.

It would be nice to take advantage of multi-rate retry, which my cards
seem to have.

I'll be experimenting further.

-- 
        Greg Troxel <gdt@ir.bbn.com>