[ntp:questions] Advices on setting up a stratum 0 NTP server

unruh unruh at wormhole.physics.ubc.ca
Wed Feb 3 17:57:22 UTC 2010

On 2010-02-02, Jos? Miguel Parrella Romero <joseparrella at gmail.com> wrote:
> (also sent to timekeepers ML)
> Hello,
> 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?
>   http://bit.ly/blZVVf
> 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?

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. 

> (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

NTP ONLY delivers utc. Linux ONLY uses UTC internally.

> 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,
> Jose
> ? 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:

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. 

>   http://bit.ly/b3kvIi

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