[ntp:questions] SNTP server + ntpd 4.2.4 client

David Woolley david at ex.djwhome.demon.co.uk.invalid
Fri Mar 14 22:43:59 UTC 2008

Noob wrote:
> I've been running ntpd 4.2.4 to synchronize my system clock using remote 
> stratum 2 servers as a reference. (The RTT to these servers is in the 
> 30-50 ms range.) The accuracy is in the 1-2 ms range, based on the 
> reported offset.

Offset doesn't tell you the accuracy, it only gives you an idea of the 
variability of the error.  Theoretically, the error could be as much as 
15 to 25ms, plus the error from the stratum one to the stratum 2.

> I've been asked to evaluate the following time server, in order to reach 
> a better accuracy than what the current setup provides.
> http://www.heoldesign.com/index.php?id=58
> (AFAIU, this time server implements SNTP, not the full NTP.)

There are many network timeservers that implement full NTP, so I'm not 
sure what they are doing with just SNTP; maybe it is aimed at the 
Windows w32time market.

Also, you can use a GPS timing receiver, with 1pps output, directly.

> The idea would be to put this (stratum 1) time server in the same LAN as 
> my box, and add it my ntp.conf. (The RTT on the LAN is on the order of 
> 100 µs.)
> Will it work?

It's a violation of NTP, so you the result will only be compliant as an 
SNTP client.  It may or may not work, depending on whether or not early 
w32time implementations conformed to SNTP.  Early versions of w32time 
didn't set enough of the response fields to sensible values to guarantee 
that ntpd would work as a client.

> Is it a problem that the time server only implements SNTP?
> What kind of accuracy may I expect?

If it works, you can probably expect most of the errors to be within 
your box.

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