[ntp:questions] ntp server help

Mikel Jimenez mikel at irontec.com
Sat Aug 9 14:55:16 UTC 2008

David Woolley escribió:
> Unruh wrote:
>> 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 
> cameras.
> 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 
> synchronizing machine.
> 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 
> experience.
> 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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How can I configure the server to cameras get server time every very 
very short time? My objective is to get the server and 4 cameras 
syncronizhed, not more 0.01s desyncronizhed, taking reference the server.

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