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...."
