[ntp:questions] ntp server help

Unruh unruh-spam at physics.ubc.ca
Mon Aug 11 00:19:59 UTC 2008


mikel at irontec.com (Mikel Jimenez) writes:

>David Woolley escribis:
>> 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.
>>
>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.

We have no idea what is running on the cameras/ There is apparently a clock
on them. Is there some sort of ntp/sntp running on them If there is your
server running ntp will automatically also act as an ntp server. If there
is no ntp running on the cameras, then I do not know. So, more information
would be helpful




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