Re: [RFT] ar9170: AP broadcast buffering

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

Christian Lamparter <chunkeey@googlemail.com> writes:

> On Monday 07 December 2009 21:08:32 Kalle Valo wrote:
>
>> I don't know what time constraints you refer to here, but clients
>> should stay awake until they have received a multicast/broadcast
>> message with the moredata bit disabled. So, in theory, it doesn't
>> matter even if the frames are transmitted even 20 ms after the beacon.
>> (In practise some hardware might have timers for this, I think at
>> least wl1251 had one.)
>
>> Of course the downside is the increased power consumption. But it's
>> still better than to not receive the multicast/broadcast frames at
>> all :)
>
> That's the thing: 802.11-2007 11.2.1.5 f) says:
> "*Immediately* after every DTIM, the AP shall
>   transmit all buffered broadcast/multicast MSDUs...".
> And I cannot rule out that some Devs took this quite literally. ;-)

Well, "immediately" is relative. If my wife says to immeaditely do
something, it might take a week before I'll do it ;)

> Anyway, here is a case that I've witnessed:
>
> During testing, I caught samples where MC/BC frames were delayed for
> more up to 115ms. (b_interval = 102.4ms and dtim_period = 3)

Yeah, if the time is longer than the beacon interval then it won't
definitely work.

-- 
Kalle Valo