[ntp:questions] NTP architecture recommendation

Richard B. Gilbert rgilbert88 at comcast.net
Thu Aug 16 21:24:21 UTC 2007

cray74 wrote:
> Hi,
> I need to update the current NTP infrastructure of our company, to
> have more accurate server internal timing (allowable offset during 24
> hours: < 3 ms). I would appreciate comments on my proposed solution:
> Topology:
> HQ localted in central Europe, plus 3 datacenters spread over the
> world (US, Asia).
> Current setup:
> two timeservers in the HQ, which sync to public NTP-servers on the
> Inet.
> Problem:
> the offset between ALL servers needs to be < 3 ms; can't put GPS-
> clocks in the datacenters (no GPS-signal); using free public NTP
> servers is not good enough (low accuracy, high jitter because of a
> number of different Inet-lines with changing latency)
> My proposal:
> 1. set up two reference clocks in two separate locations in Europe
> (where we got offices), each setup consisting of:
> a) Meinberg Lantime M300 GPS with OCX LQ or even MQ in the office (ie.
> where I can get the GPS signal)
> b) Meinberg Lantime M300 MRS (no GPS antenna, just a precise internal
> clock) in the server room (this one syncs to the first one)
> 2. the datacenters in the US/Asia will each contain one Meinberg
> Lantime M300 MRS, syncing to the main 2 stratum 1 servers
> Question:
> 1. Will this setup guarantee me the required accuracy?
> 2. Can the same be achieved with less investment?
> Thanks for your feedback!
> Cheers
> db

The quality of the source clocks is usually less important than the 
quality (delays and jitter) of the network path between server and 
client.  Many of the stratum 1 internet servers have local atomic 
clocks, GPS receivers, LORAN, etc.  They KNOW what time it is to within 
a microsecond or better.  It's the network path between you and the 
servers that craps all over the quality of the time received!

I would look harder at getting GPS receivers to work at the data centers
or, perhaps, a CDMA based solution.  You can get a refclock from 
Symmetricom that can lock onto the reference signal of a CDMA base 
station.  This should work anywhere that a CDMA cell phone will.

Your Meinberg M300 MRS is probably capable of keeping time very well; 
the problem will be how to set it with an error less than 3 milliseconds!

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