Re: wireless: recap of current issues (configuration)

[Stuffed Crust <pizza@shaftnet.org>]

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On Mon, Jan 16, 2006 at 09:07:52PM +0200, Samuel Ortiz wrote:
> That is true, thin MACs usually don't filter beacons on the same channel.
> But in some cases (mainly power saving), you really want to avoid
> receiving useless beacons and having the host woken up for each of them.
> You may even want to not receive all the useful ones (the ones coming from
> the AP you're joined with) if your softmac allows that.

BSSID filtering doesn't matter as far as 802.11 powersave is concerned
-- the power savings come from disabling the RF/BBP components.  In
other words, you can't receive or transmit traffic.

If you're respecting the AP's beacon interval/DTIM settings, you only 
wake up every couple of beacon intervals and listen for a beacon.  IF 
there's traffic waiting for you, then you wake up your transmitter, send 
out a PSPOLL (or NULL/PSEnd) frame, get your traffic, then go back to 
sleep again.  

You may hear another beacon when the STA is awake, you may not.  BSSID 
filtering has nothing to do with 802.11 power save, but rather is 
intented to reduce the host load (interrupts, processing overhead) and 
thus the host power consumption.

> This kind of beacon filtering is a big power saver, which is one of the
> most important requirement for some platforms (phones, PDA, etc...).

You need to be clear if you're talking about 802.11 powersave, versus 
"power savings stemming from reducing the load on the host system", 
which is where BSSID filtering is beneficial.

 - Solomon
-- 
Solomon Peachy        				 ICQ: 1318344
Melbourne, FL 					 
Quidquid latine dictum sit, altum viditur.

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