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I've been spending every waking moment reading 802.11n for a while now. This is one complicated document. Remember "Protection Ripple"? Get ready for a tidal wave of protection ripple - thanks to a little field called "OBSS Non-HT STAs Present". This is a field in the HT IE of Beacons, Probe Request frames, etc that lets other APs know if there is a need for them to protect greenfield and RIFS sequence transmissions due to a non-HT STA being present. In a nutshell, this is a mechanism where one AP can indicate to another adjacent AP whether or not it should use protection mechanisms - of which there are now MANY in 802.11n.

One thing to note is that the indication of the need to use protection should not extend beyond 1 adjacent AP; however, as non-HT and non-ERP stations roam and reassociate, this will cause major protection status flipping as they move. It'll still be Ripple Hell.

hideous.

Hi,

Can you explain me clearly, Under what are the conditions the "OBSS non-HT STA present" sub field is set to 1.

http://www.cwnp.com/community/articles/802.11n_protection_mechanisms_part_1.html

Section III

Thank you very much.