[ntp:questions] Re: time

Richard B. Gilbert rgilbert88 at comcast.net
Mon Nov 28 19:46:48 UTC 2005


K wrote:

>Hi,
>
>
>
>What are some good ways to get time?
>
>I know about NTP v3 and v4 and use it on some systems.  I need a time
>accuracy of < 1 ms.
>
>
>
>NTP over gigabit Ethernet is down to what time of precision?   1ms?   Does
>anyone have any data on this?
>
>
>
>I know that the linux os is compiled for something like 1 ms precision
>
>IRIG is a pain?  Is there anything better?
>
>
>
>Thanks in advance
>
>  
>
I'm running two Sun Ultra 10 workstations in my home.   Sunblok runs 
Solaris 8 and ntpd 4.0 with a Motorola  Oncore M12+T GPS receiver as a 
hardware reference clock. Sunblok is my ntp server.  It is connected to 
Sunbitch (Solaris 9, ntpd 4.0) via 100mb full duplex switched Ethernet.  
ntptime on Sunbitch reports an estimated error of 71 us.   It also 
reports a maximum error of 128,000 us or 128 ms.  I believe the maximum 
error represents a theoretical worst case rather than meaning the local 
clock was actually off by 128 ms at any recent time.

So it can be done.   I think that the Motorola GPS has a great deal to 
do with it.  If  Sunblok were synchronized to the best available 
internet servers instead of a hardware reference clock, its local 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.

Success will also depend on the hardware and O/S running on the client.  




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