[ntp:questions] ntp server help
david at ex.djwhome.demon.co.uk.invalid
Sat Aug 9 14:40:21 UTC 2008
> mikel at irontec.com (Mikel Jimenez) writes:
> And you are using ntpdate why? Why not set up ntp on the system and use it
> to discipline your system's clock. Note whether you will get 1/100 sec
> accuracy depends on the network etc.
Although it isn't particularly clear, I believe he is running ntpdate on
a machine that is properly synchronised, to measure the offsets of the
Of course, the error in the cameras may well be an order of magnitude
better than the offsets measured, either that way, or the more approved
way of using configuring the cameras as ignored servers on the
However, my gut feeling is that this application required that it be an
explicit requirement to buy the cameras that they maintain an offset
less than 10ms. If that was the case, then he should be pursuing this
with the vendors of the cameras. If not, he should put it down to
It seems unlikely to me that the cameras are runing NTP, rather than a
basic implementation of SNTP, and even if they are running NTP, it is
unlikely that they have included any of the recent optimisations for
fast convergence, so he should be waiting several hours, after powering
up the cameras, before doing anything critical.
It's also worth noting that one really needs a local radio reference
clock (although I suspect he's actually using the local clock as
reference) to guarantee 10ms accuracy on the server. It is possible to
get this most of the time with an internet time reference, but some care
is needed to achieve it all the time.
> And why are you comparing the offset?
He wants the video feeds from the cameras to have their RTP timestamps
within 20ms (probably he meant 10ms) of each other. I'm not sure why,
as it would seem easier to retime outside of the camera. I'm guessing
the RTP bit.
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