[time-nuts] can of worms: time-of-day in a community radio station

[David J Taylor]

Hi David, I don't particularly trust NTP servers from pool.ntp.org (I
assume that is what you mean by "pool"), and I use public stratum-1
servers chosen from a public list. Of course I make sure that my usage
complies with the policies and terms of use for each server (some
allow regional use only, some say do avoid using iburst keyword, some
require prior permission and/or notification).
I have found that using 3 to 5 public stratum-1 servers works very
well, and gives a time synchronization which is within 3 to 5
milliseconds when compared with a reference timing board with GPSDO.
This time offset discrepancy is actually due to the fact that my ISP
(comcast cable) has asymmetric send/receive delays. It disappears when
I tried this setup at my office, which has symmetrical fiber optic
connection to internet.

Your point about avoiding having all the internal machine hit
stratum-1 servers is a good one however. To avoid that in my setup I
designate 3 machines which serve as an internal stratum-2 pool for
internal distribution. Each of them has 3 to 5 external NTP stratum-1
servers and they all peer with each other. Then every other internal
machine uses these 3 machines. I have more details on my setup in my
reply to Eric.

Kind regards,

-- Fio Cattaneo
=====================================

Fio,

I'm surprised you don't trust "pool" servers.  My experience is that using 
the pool directive, and allowing NTP to expand its server list automatically 
to the maximum number of servers, gives good results usually with one of two 
servers at least being stratum-1 GPS-locked.  That's using UK and NL 
servers.  I suppose if you have a poor or overloaded internet connection 
server quality doesn't matter as much - well, almost.  My ISP is 200/20, and 
used to be 200/12.  Talk about asymmetric!

If you have a PPS feed from that GPS board, you could easily add it to a 
Linux PC (Raspberry Pi, for example) or even a Windows box and use that 
locally as your own stratum-1 server.  I never had much success with 
peering - it seemed that when one server had a higher offset for whatever 
reason it dragged the other with it.  I use multiple independent stratum-1 
servers - one a Linux X86, one a Raspberry Pi, and one LeoNTP box.

Cheers,
David
-- 
SatSignal Software - Quality software for you
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Email: david-taylor at blueyonder.co.uk
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