RE: HT capabilities IE

[Johannes Berg <johannes@sipsolutions.net>]

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On Wed, 2008-10-08 at 10:33 -0500, Nils Bagge wrote:
> My humble opinion is yes, the HT capabilities field should be constant,
> from the perspective of a typical AP.

Yeah I totally agree.

> Practically speaking, I doubt that an AP would want to toggle SM power
> save at all, let alone on a per-beacon basis, as historically power
> consumption is not as critical at the AP vs. at the client.

True.

> But, if you want to be 'green'... (I can see how this would benefit a
> 'low power AP') The only problem I see is with the AP entering 'static
> SM power save'. You might run into interoperability trouble with varying
> behavior of client STA's, due to different interpretations of the
> standard or assumptions. It wouldn't surprise me if some clients ignore
> changes to the HT capabilities IE once associated, or if some ignore the
> SM power save field in beacons entirely. Hence, they could transmit a
> 2-stream MCS which would not be decodable with a single RX chain.
> 
> Theoretically, the only SM power save mode I'd recommend for an AP is
> dynamic SM power save. 

Right, but if you enter dynamic SM PS then it doesn't matter much
anyway, does it? I mean, there's no protection requirement in that case,
is there? Or am I reading it wrong? I _think_ I will handle the SM PS
change in mac80211, but I'm not entirely sure right now.

johannes

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