[ntp:questions] Synching to a Legacy System as an External Clock Reference

Richard B. Gilbert rgilbert88 at comcast.net
Fri May 18 00:15:08 UTC 2007


michael.antinucci at lmco.com wrote:
> Greetings!
> 
> 
> 
> Here is the problem I am trying to solve:
> 
> 
> 
> I have an old legacy external system that I need to synchronize with
> that sends custom protocol UDP packets containing a single field in
> the packet that contains the legacy system's current clock time (in
> milliseconds). The current clock time starts at 0 when the system
> boots and increments forever thereafter. The frequency of this message
> is at least every 10 seconds, not 1 PPS like I would like.
> 
> 
> 
> My internal system is a large scale distributed Linux-based NTP-
> synchronized (down to 1 millisecond resolution) system. I have a
> single NTP server that all the other nodes in my internal system
> synchronize to. My internal system's NTP server is not currently
> synchronized to anything else and is operating as the "master".
> 
> 
> 
> My hope is to have my internal system's NTP server receive the 10
> second clock pulses from the old legacy system over UDP and have my
> internal system's NTP server synchronize with it. Is this possible?
> Any other ideas?
> 
> 
> 
> I read this fine article (which I think is the path to take) but I
> need a clearer explanation on what to do.
> 
> 
> 
> http://www.ee.udel.edu/~mills/ntp/html/extern.html
> 
> 
> 
> Any help would be greatly appreciated!
> 

I think that, in the article you refer to, Dr. Mills is referring to a 
system or a hardware clock that actually knows what time it is!

Your external system has no clue what time it is as we understand it. 
It just ticks periodically and the period is apparently "approximately 
ten seconds"

Your external system apparently does not run speak the NTP protocol.  As 
matters stand, there is no way you could use NTP to synchronize to that 
server nor can I see why it might be worth the effort if you could!

NTP was intended to be hierarchical with an atomic clock at the peak of 
the hierarchy.  A system that gets it's time directly from that atomic 
clock is at "stratum 1".  Any system or device that gets time from a 
stratum 1 device is at stratum 2 and so on.

What problem are you trying to solve here?  Since your internal systems 
are already synchronized using NTP, it should be fairly trivial to 
install ntpd on the external system and get it synchronized too.




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