[ntp:questions] Re: SNTP Client/Server questions

Harlan Stenn stenn at ntp.isc.org
Tue Aug 15 22:50:18 UTC 2006


>>> In article <1155648559.784059.118920 at 75g2000cwc.googlegroups.com>, david.lindauer at honeywell.com writes:

david> I've got a question about the rationale behind the SNTP RFC2030.
david> Basically, a valid SNTP server is supposed to be sourced directly
david> from a reference, never from a remote NTP server.  We believe this is
david> because of the lack of sophisticated algorithms as found in NTP; e.g.
david> sourcing an SNTP server from an NTP server is going to be inherently
david> less accurate.  Is that the gist of it, or is there other rationale
david> as well?

Yes, to the best of my knowledge.

david> Also, assuming an SNTP client is doing similar to the spec and
david> aliasing the server time with a calculated propagation delay, and
david> assuming a LAN rather than the internet at large, can anyone give a
david> general feel for how far off the client is going to be from its
david> server?

It depends on how good the system clock is and how often sntp polls.

david> Finally, are those equations for round trip time and propagation
david> delay in RFC2030 actually correct?  They aren't what I would expect,
david> and don't even seem to match each other.

Please see the updated/newer RFC:

 http://ntp.isc.org/Support/NTPRelatedRFCs

H




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