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. 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? Thomas _______________________________________________ Devel mailing list [email protected] http://lists.open80211s.org/cgi-bin/mailman/listinfo/devel
