Re: Testing AP mode with WLAN-USB-Stick: How to obtain?

[Kalle Valo <kalle.valo@iki.fi>]

Johannes Berg <johannes@sipsolutions.net> writes:

> On Wed, 2009-06-10 at 17:22 +0200, Gábor Stefanik wrote:
>> On Wed, Jun 10, 2009 at 3:39 PM, Hin-Tak Leung<hintak.leung@gmail.com> wrote:
>
>> (Note that I'm also for allowing such "buggy" AP mode on devices
>> without a HW multicast buffer, perhaps with hostapd spitting out a
>> big, fat warning on startup; but Johannes has the final say in
>> mac80211-related questions.)
>> 
>> (To Johannes: exactly why is it required for the multicast buffer to
>> be in hardware?)
>
> It isn't required, ath5k/9k don't have it there, they have the notorious
> "CAB" queue for sending frames directly after the beacon. So does b43,
> and probably other designs. The problem really is that powersave mode is
> very important for small clients like your mobile phone or digital
> camera, or even bluetooth3 device, and not doing multicast buffering
> correctly means that either those devices get into weird unreachable
> states, or you need to turn off powersaving features on them which makes
> the battery drain unbearable.

Not only mobile clients, but as we are talking about enabling power save
by default, also Linux laptops would have problems.

> Now, it may or may not be possible to work around this in software by
> sending out the multicast frames on a high-priority queue right after
> the beacon,

And the DTIM beacon should have the broadcast/multicast TIM bit set
before sending the frames.

> or something like that, but frankly I'm not interested in working on
> zd1211rw myself, so that will have to be somebody who is (a) familiar
> with 802.11 powersaving and multicast buffering, (b) wants zd1211rw to
> work, and finally (c) has a lot of time to play with the device.

If someone really has that much time, I think it's better to spend it on
more important issues than this.

-- 
Kalle Valo