[ntp:questions] Query about NTP accuracy

Unruh unruh-spam at physics.ubc.ca
Fri May 22 18:47:30 UTC 2009

>NTP v4 over the LAN would be just as bad as V3. Think about broadcast or 
>multicast!  That way you don't clutter up the net with queries and 
>response.  Instead, every N seconds your server announces: "at the chime 
>the correct time. . . ." and your clients can adjust their clocks as 
>necessary.  Your broadcast and/or multicast clients will exchange 
>packets initially in order to establish the round trip delay.  After 
>that initial volley, the clients just sit and listen.

The amount of traffic is completely trivial. Even if you have 10000
machines, and run at poll interval 4, that is less than a few KB/s
traffic on your lan. And broadcast IS much less accurate than direct
connection. No matter that you calibrated round trip time, that round
trip time changes during the day. I have never done a test of exactly
how much worse broadcast is so cannot supply figures.

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