Advices on setting up a stratum 0 NTP server

Advices on setting up a stratum 0 NTP server

Post by JosMiguel » Thu, 04 Feb 2010 05:44:54

Hash: SHA256

(also sent to timekeepers ML)


I'm looking forward to help a local refclock owner (cesium std and GPS
receiver) setting up an NTP server. They're Symmetricom users.

They have a CS-III cesium standard, which is queryable via RS232, but I
wonder if I'll be able to use it from a NTP-enabled Linux box. I've read
about the PPS clock discipline driver, and I know I'll probably need to
build some cables around. And I'll also need a refclock.

Moving forward, their XLi GPS receiver has an Ethernet port, but I still
have to check if NTP support is enabled (seems like a commercial option)
but it seems so since they provided me with addressing information. Is
there any other option for it?

Finally, they have a time display which connects via BNC, I assume to
the GPS and maybe also the cesium std.

So, I'd really appreciate your advice on:

(a) Should I ditch the cesium clock and go ahead and just do the
networking to get the GPS receiver with NTP support out to the Internet?

(b) Should I setup an additional Linux server with NTP and use the
serial connection to take profit of the cesium clock? Maybe also peer
this server with the NTP server on the GPS receiver?

(c) I'm not 100% certain ATM but this clocks might be setup to serve a
local timezone, and not UTC. And I'm not aware if ntp.conf allows me to
say: hey, please don't try to convert this. I believe they are not UTC
since they're connected to a talking clock, which I don't think has the
ability to timezone UTC signals
I'd also like to clarify that I need to check and measure connectivity
out there before thinking of adding this to the pool, but initially they
will grant me permission since I already convinced them that getting out
of their cesium-powered rooms is a good thing for everyone.

Thank you very much for your tips and I hope to hear back soon,

When Venezuela switched from UTC-0400 to UTC-0430, there was a public
TV broadcast where the refclock manager just adjusted it by hand, but
then again I don't think that was the standard but maybe just the clock
that it's been displayed. He then adjusts the talking clock:
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Advices on setting up a stratum 0 NTP server

Post by unru » Fri, 05 Feb 2010 02:57:22

The chief problem with the timekeeping is the computer. The crystal is
very temp sensitive, so that the thermal fluctuations ( running
programs, daily temp changes, etc) will mean that the computer itself
cannot do better than a few usec of accuracy. Since GPS can deliver time
to the computer better than 1usec, unless you have a temp controlled
crystal on that motherboard, GPS is more than accurate enough.

Also as an ntp server, the network time delays etc add at least 10usec
of jitter ( more like 100 but lets say 10)

The problem with ntp is its very slow response to temp changes for
example. chrony is much faster and thus has better timekeeping.

NTP ONLY delivers utc. Linux ONLY uses UTC internally.

It is the display I assume. National time standards work on UTC as well.
Mind you maybe the govt has set up a new time standard.