[time-nuts] time transfer over wifi

jimlux jimlux at earthlink.net
Sun Jan 15 10:06:32 EST 2017

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 

so this "new thing" will be hardware of some TBD form.

But more interesting to time-nuts, I think, is how do you do it without 
the new hardware.

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

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

More information about the time-nuts mailing list