[ntp:questions] Re: isolated network + accuracy
Richard B. Gilbert
rgilbert88 at comcast.net
Mon Dec 13 18:47:21 UTC 2004
>Thx really for the answer... If i have understand
>correctly the problem of not having good accuracy is a
>problem of my server because it always loses
>If i connect the server to the internet under a
>stratum 2 server, do u think that the server can
>achieve accuracy below 1 ms? Do u think i must
>configure the server in a specific way for my
>After finishing with the server then the clients can
>achieve synchronization with accuracy of 1 ms or this
>is still impossible? The major problem is that i want
>all the clients to be synchronized and each of them
>has an accuracy of 1 ms or less.
>Really thank u!
>Have a nice day
>--- "Richard B. Gilbert" <rgilbert88 at comcast.net>
>>>Goof morning. I have an isolated network and i want
>>>achieve accuracy smaller than 1ms. Do u know if
>>>is possible? How i must configure the clients for
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>>Without a stable source of time, I'd say that
>>synchronization within 1ms
>>is not possible. The typical, unsynchronized,
>>computer clock is neither
>>stable nor accurate.
>>You will need a hardware reference clock of some
>>sort. A cesium
>>frequency standard (with clock option) is the best
>>there is. It's also
>>extremely expensive. A rubidium standard is second
>>considerably cheaper but still expensive to buy and
>>maintain. A GPS
>>timing receiver can be obtained for less than $500
>>US and is a very good
>>choice if you can place an antenna where it has an
>>unobstructed view of
>>the entire sky. An oven controlled quartz crystal
>>provide a stable source.
>>Configure one computer with attached hardware
>>reference clock as the
>>server. Configure the clients to get their time
>>from the server.
>>Don't expect much from Microsoft Windows in the way
>>of accuracy; the
>>clock resolution is too low and the operating system
>>tends to lose
>>interrupts (clock ticks) when it is busy doing
>>something else. Linux
>>also has been known to have problems with losing
>>questions mailing list
>>questions at lists.ntp.isc.org
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If your server loses interrupts, I'd say you have no hope of achieving
Using an internet server as a time source will almost certainly not
allow you to achieve 1ms accuracy! 10ms accuracy is possible over the
internet but cannot be guaranteed.
Many many computer operating systems update their clocks at intervals of
10ms or longer. In a system updating at 10ms intervals, the time
reported at any random instant can be wrong by as much as 9.9999999999.
. . ms and, on average, will be within 5ms of the correct time.
1ms accuracy is a very high standard and quite difficult to meet. I
don't believe that Windows is capable of it. Linux may not be
either. Some flavors of Unix are capable, at least in principle. I
believe that Solaris is. I lack sufficient recent experience with other
flavors of Unix to offer an informed opinion.
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