On Tue, Oct 4, 2016 at 11:57 PM, Gucea Doru <gucea.doru@xxxxxxxxx> wrote: > On Tue, Oct 4, 2016 at 3:37 PM, Krishna Chaitanya > <chaitanya.mgit@xxxxxxxxx> wrote: >> On Tue, Oct 4, 2016 at 5:09 PM, Gucea Doru <gucea.doru@xxxxxxxxx> wrote: >>> On Sat, Oct 1, 2016 at 2:52 PM, Arend van Spriel >>>> <arend.vanspriel@xxxxxxxxxxxx> wrote: >>>>> >>>>> >>>>> On 29-09-16 13:32, Gucea Doru wrote: >>>>>> On Tue, Sep 27, 2016 at 12:03 PM, Gucea Doru <gucea.doru@xxxxxxxxx> wrote: >>>>>>> What is the decision triggering the exit from the PS mode immediately >>>>>>> after the ping request? I am asking this because 802.11 PS legacy >>>>>>> specifies that the client should wait for a beacon with TIM set in >>>>>>> order to wake up: in my case, there is no beacon between the ping >>>>>>> request message and the Null frame that announces the exit from the PS >>>>>>> mode. >>>>>> >>>>>> >>>>>> Any help would be highly appreciated :) >>>>> >>>>> Actually though I already sent you are reply, but alas here it is. >>>>> >>>>> bcmdhd is our aosp driver. I am maintaining the upstream brcm80211 >>>>> drivers. Regardless your question is more for firmware running on the >>>>> device. So like the same behavior would be observed when using brcmfmac >>>>> with same firmware. >>>>> >>>>>> IEEE Std 802.11-2012, section 10.2.1.8 specifies that "when the STA >>>>>> detects that the bit corresponding to its AID is 1 i the TIM, the STA >>>>>> shall issue a PS Poll". In my capture there are cases when the STA >>>>>> exits the PS mode without waiting for a beacon. >>>>> >>>>> It is a bit tricky, but the standard does not explicitly say the STA >>>>> should be in power-save at any other time. So it is difficult to say >>>>> what event occurred on the STA side to exit PS mode. Also STA means >>>>> P2P-Client as you say. That means that you have multiple interfaces: >>>>> regular STA and P2P-Client. So is the STA connected to some other AP or >>>>> just not connected. wpa_supplicant will do intermittent scan or initiate >>>>> scheduled scan by which firmware will scan at a certain interval. That >>>>> is just some things I can come up with and I am sure there are more. >>> >>> I agree that there may be some events belonging to the regular STA >>> interface that could trigger the Null Frame (which includes the exit >>> from PS Mode). However, I would expect to see some management frames >>> in the air before/after the Null Packet (e.g.: a Probe request in case >>> of a scheduled scan). But in my case the trigger for the Null frame >>> seems to be the ping request packet, the scenario is the same every >>> time: ping request -> Block ACK -> Null Frame (Wireshark trace >>> confirms this behavior). >>> >>> I thought that you had a power save optimization algorithm that keeps >>> the card on a few milliseconds just to see if we can have a fast reply >>> from the peer. Does this ring a bell? :) >>> >>> On Sat, Oct 1, 2016 at 3:02 PM, Krishna Chaitanya >>> <chaitanya.mgit@xxxxxxxxx> wrote: >>>> Keeping the STA aside, as far as AP is concerned the STA is still in PS, >>>> so it should set the TIM/DTIM bit to 1 before sending out data to the STA. >>> >>> Not necessarily, see section 10.2.1.6/l from IEEE Std 802.11-2012: >>> "When an AP is informed that a STA has changed to the Active mode, >>> then the AP shall send buffered BUs (if any exist) to the STA without >>> waiting for a PS Poll...." >> Yes, but in this case the STA did not inform AP (as per sniffer captures)? >> so AP should set TIM/DTIM... > > The STA _did_ inform the AP. > > If you take a look at the packet traces you'll see that the STA sends > a NULL frame saying that it will exit Power Save Mode. According to > the specification the AP can send the buffered frames. Yeah, sorry i thought AP is sending the ping request. But still as STA is sending "ping request" with PM=0, the state at AP should be updated treating STA as active, so sending NULL data + PM=0 is redundant. -- Thanks, Regards, Chaitanya T K.
