[ntp:questions] Isolated Network Drift Problem

Richard B. Gilbert rgilbert88 at comcast.net
Tue Nov 25 19:10:15 UTC 2008

Cal Webster wrote:
> On Tue, 2008-11-25 at 09:43 -0500, Richard B. Gilbert wrote:
> [...]
>>> What's the best way to determine which of our NTP servers provides the
>>> best local clock?
>> Consider that the Garmin GPS18LVC has a pulse per second output and 
>> costs less than $100 US.  If you can site an antenna with a good view of 
>> the sky, you can have a stratum 1 server of your very own and have the 
>> time accurate to within a millisecond or less.  Note that while the GPS 
>> is accurate to 50ns or better the process of getting the time into your 
>> computer may introduce several hundred microseconds of uncertainty.
> Interesting... We'd have to run a long cable though, the computer lab
> has no windows and the roof is the most logical place to put an antenna.
> I don't think USB will handle that much line loss. It's a single story
> section of the building so we're probably talking about 100 meters or so
> to get a view of the sky. I'll need a version that can handle the remote
> distance. I'll request a purchase but it could be months before we see
> it. 
> After a bit of googling I found an excellent write-up on how to use one
> of these for an NTP server [http://time.qnan.org/ "Using a Garmin GPS 18
> LVC as NTP stratum-0 on Linux 2.6"]

Your NTP server need not live in a computer room; it can be anywhere 
that you have a LAN connection!  A PC that has been retired from desktop 
service can be recycled as an NTP server.  A "486/33" has more than 
enough computing power to be an NTP server.  You'll probably have to 
settle for a Pentium because I think the museums have cornered the 
market in 486s! ;-)

Some flavor of Linux would be a good choice of O/S.

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