Here is a ti app note with timestamping hardware wl8 but ordinary ap's with no special protocol just timestamping the beacon frame.
http://www.ti.com/lit/an/swaa162a/swaa162a.pdf On Sun, Jan 15, 2017 at 10:06 AM jimlux <[email protected]> wrote: > Returning to the OP > > "A TimeSync certification program will appear later this year, but > > semiconductor firms will have to create new Wi-Fi chips including the > > feature." > > > > so this "new thing" will be hardware of some TBD form. > > https://www.wi-fi.org/discover-wi-fi/wi-fi-timesync > > > > > > > > But more interesting to time-nuts, I think, is how do you do it without > > the new hardware. > > > > http://www.cse.msu.edu/~glxing/docs/WizSync.pdf > > says, in part: > > > > 802.11 requires all APs to broadcast periodic beacon frames that > > carry important management information (e.g., supported rates and > > security settings). The default beacon period is 102.4 ms, which is > > rarely changed on production APs. ...However, as defined in 802.11, > > whether a beacon frame is delayed or not, the subsequent beacon > > frame shall always be scheduled at the undelayed nominal beacon interval. > > > > so this is the "use a 1pps, but throw out outliers" kind of strategy... > > > > And there would need to be some sort of measurement of the AP's timing > > error - they make the assumption that the timing of the beacons is > > driven by a clock with max 25ppm error (as required by the 802.11 std), > > although they've measured <5ppm normally > > > > Ultimately, they got on the order of 0.1 0.2 ms. > > > > > > That's a few orders of magnitude worse than "microsecond", but it's also > > an interesting read. > > > > > > > > an older presentation (2006) might be useful > > > http://www.ieee802.org/1/files/public/docs2006/avb-stanton-wifi-timesync-intro-060613.pdf > > > > discusses 802.11v > > > > there's been a lot of stuff on time sync/distribution over 802.11 links > > for the last decade.. maybe this CES announcement is more about "we at > > WiFi alliance are ready to market it". Has anyone gone through the > > 802.11 standards list recently? It might well be that the standard is > > already there. > > > > 802.11aa says "Amendment 2: MAC Enhancements for Robust Audio Video > > Streaming" in the description... although that might just be things > > like QoS and access control-digital rights management > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
