On 12/11/2013 10:00 PM, Thomas Pedersen wrote: > On Wed, Dec 11, 2013 at 12:57 PM, Thomas Pedersen <[email protected]> wrote: >> On Wed, Dec 11, 2013 at 3:31 AM, Marco Porsch <[email protected]> wrote: >>> I am not perfectly sure if the TBTT Adjusting subfield is used correctly >>> now. It would be good to clarify what it is really used for. >>> >>> a) the TBTT Adjusting subfield shows that _the next beacon_ will be delayed >>> due to clock drift adjustment >>> b) the TBTT Adjusting subfield shows that _this beacon_ is delayed due to >>> clock drift adjustment >>> >>> a) makes more sense in my perspective: >>> - to a sleeping peer STA it hints that it should expect the next beacon to >>> be delayed (to adjust wakeup timers/timeouts) >>> - 13.13.2.2.3 says a peer STA "shall invalidate the T_offset value for this >>> neighbor STA and shall not perform [T_offset and T_ClockDrift >>> calculation]". On next beacon receipt with new timing and without the TBTT >>> Adjusting subfield it will start recording valid T_offset values again. In >>> case b) it would waste one valid T_offset value. >> >> Agreed, except if we follow a) and the TSF adjustment (if the pre-tbtt >> interrupt delay is large enough) happens before the actual >> (now-delayed) TBTT, receiving peers will incorrectly interpret TSF >> adjustment as clock drift. It is unfortunate we have to punt TSF >> adjustment to the workqueue, but either way I think it makes sense for >> the adjust_tbtt callback to advertise TSF adjustment in the beacon >> right away. > > Sorry I misunderstood your question, you were asking about the meaning > of the TBTT Adjusting subfield.
Sorry, I should have mentioned earlier that I see a) and b) from the perspective of the transmitter, not that of the receiver. So on the transmitters side I see a) as announce-before-doing and b) as announce-while-doing. And my guess is that the standard intends a) while the current patch implements b). > 13.13.2.2.3 says: "The mesh STA checks if the transmitter of the > Beacon frame or Probe Response frame is in the > process of the TBTT adjustment (see 13.13.4.4.3). If the received > frame contains the Mesh > Configuration element and the TBTT Adjusting subfield in the Mesh > Configuration field is 1, the > mesh STA shall invalidate the Toffset value for this neighbor STA and > shall not perform the > following steps.". So it seems the TBTT Adjusting subfield referes to > _this_ beacon? So here we are on the receiver side. This part is actually pretty clear from 13.13.2.2.3. _______________________________________________ Devel mailing list [email protected] http://lists.open80211s.org/cgi-bin/mailman/listinfo/devel
