On Tue, Oct 4, 2016 at 3:37 PM, Krishna Chaitanya <chaitanya.m...@gmail.com> wrote: > On Tue, Oct 4, 2016 at 5:09 PM, Gucea Doru <gucea.d...@gmail.com> wrote: >> On Sat, Oct 1, 2016 at 2:52 PM, Arend van Spriel >>> <arend.vanspr...@broadcom.com> wrote: >>>> >>>> >>>> On 29-09-16 13:32, Gucea Doru wrote: >>>>> On Tue, Sep 27, 2016 at 12:03 PM, Gucea Doru <gucea.d...@gmail.com> 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.m...@gmail.com> 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.
