[ntp:questions] Re: time

K spam at nospam.com
Wed Nov 30 15:42:19 UTC 2005


Hi,

So to summarize you guys.  I think that you are saying that
ntpd v3 is accurate on a gigabit network that is congested  to 5-20ms  is 
the accuracy is a reasonable expectation. What about IEEE 1588, since this 
is also ethernet bases can I get any better time accuracy with that?





"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in message 
news:7sGdnUDrE9TZvhDeRVn-hQ at comcast.com...
> Bjorn Gabrielsson wrote:
>
>>"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
>>
>>
>>>K wrote:
>>>
>>
>>
>>>>I know about NTP v3 and v4 and use it on some systems.  I need a time
>>>>accuracy of < 1 ms.
>>>>
>>>>I know that the linux os is compiled for something like 1 ms precision
>>>>
>>
>>?
>>
>>>So it can be done.   I think that the Motorola GPS has a great deal to
>>>do with it.
>>
>>The motorola should carry you down towards 1us, but K was only asking
>>for a thousand times less accuracy... :-)
>>
>>
>>>clock would be much less stable.  10 ms is about the best accuracy I
>>>would expect from a client synchronized to a server that synchronized
>>>over the internet.
>>>
>>
>>Even with a DSL-line - if its not overloaded - sub 1ms is easily
>>attained with good internet servers. Looking at a machine with four
>>external servers, I get see,
>>
>>/usr/sbin/ntpq  -c pe
>>     remote           refid      st t when poll reach   delay   offset 
>> jitter
>>==============================================================================
>> LOCAL(0)        73.78.73.84      5 l   25   64  377    0.000    0.000 
>> 0.001
>> xxx             .PPS.            1 u  219  256  377   11.476   -0.235 
>> 0.779
>> xxx             .PPS.            1 u  102  256  377   17.818   -0.140 
>> 75.660
>> xxx             .PPS.            1 u  217  256  377   21.575    0.203 
>> 0.235
>> xxx             .PPS.            1 u  192  256  377   20.889    0.385 
>> 0.142
>>
>>This machine usually have two GPS-refclocks and they show no
>>systematic offsets wrt the Internet servers.
>>
>>--
>>
>>    Björn
>>
> Either your internet connection, your internet servers, or both are far 
> better than mine.  I have broadband cable.  My NTP server, Sunblok, uses 
> five internet servers in addition to the Motorola GPS reference clock. 
> The internet servers show systematic offsets with respect to GPS of +1 to 
> +5 ms.  There are also seemingly random spikes in the time received from 
> the internet servers of +/- 5 to 20 ms.  When the GPS is not running, ntpd 
> tends to synchronize with a different server every few minutes which does 
> nothing for the stability of the clock. 





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