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

[Johannes Berg <johannes@sipsolutions.net>]

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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:

> > I was talking about the client suspending/resuming (i.e. the client
> > disappearing).

Which isn't relevant for answering the question why there's no AP mode
in zd1211rw, regardless of whether it has problems or not.

> (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.

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, 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.

johannes

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