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I've never paid much attention to the rates that ACK frames are returned at. However, in the last week I have, and been surprised by what I've seen.

I seem to remember that, at one time, ACK's were supposed to be sent at the same speed of the frame they were responding to.

Lately I've seen 54Mbps frames ACK'ed at both 24 and 36 Mbps by D-link and Linksys AP's. The older Cisco AP I tested seemed to only respond at the same rate, but I didn't give that a very long test.

Tonight on the net, I found a recommendation to reply at 24 Mbps fo all "g" transmissions.

What's up here? Have the standards changed? The philosopy behind it all?

And I guess the real question behind this post, has anyone seen problems when the "same rate" rule has been violated?

OK. I re-read the standard (9.6.0). So contrary to some sources, it doesn't have to be at the same rate.

It should be at the same, or lower rate - given a few other conditions (e.g no PBCC or IR Acks for an ERP-Frame - ha).

It does look like you could get into some troubles if you disabled [u]all[/u] of the Mandatory rates, e.g. 6, 12, and 24 for the ERP rates, and had some other issues at the same time.

There is some familiar IEEE obfuscation in this section, and except for the alternative that is given about other frames with the same duration (?), that's what the standard says.