[time-nuts] Minor NTP Issue?

Greg Dowd GDowd at symmetricom.com
Wed Nov 10 06:02:10 UTC 2010


My guess is that the error is real and coming from the TS2100.  The
TS2100 was (is) a SNTP server running a RTOS but the timestamps are done
at the application layer.  If you look at the output 1pps of the TS2100,
my guess is that it will probably agree with your other devices within a
few microseconds.  I don't recall doing anything in that device to
compensate for the asymmetries in the transmit and receive paths.  If
you only use the device for ntp service, you can use the pdelay (antenna
propagation delay) setting to bias the server clock to generate messages
on time.



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Jason Rabel
Sent: Monday, November 01, 2010 9:06 AM
To: time-nuts at febo.com
Subject: [time-nuts] Minor NTP Issue?

I hope this doesn't get mangled too much via email... Below is an output
of "ntpq -p" on one machine.

     remote           refid      st t when poll reach   delay   offset
jitter
========================================================================
======
*NET4501-1       .GPS.            1 u   36   64  377    0.724    0.022
0.100
+NET4501-2       .GPS.            1 u   22   64  377    0.801    0.038
0.132
+PRAECIS         .GPS.            1 u   14   64  377    0.740    0.097
0.034
-TS2100-1        .GPS.            1 u   50   64  377    4.995   -0.362
0.030
-TS2100-2        .GPS.            1 u   17   64  377    4.966   -0.331
0.035


My two TS2100's always seem to be slightly "off" compared to my other
time servers... Even after I've had to power cycle all my
equipment. Four of the five devices are currently on the same GPS
antenna and have more or less the same length of cable. Same four
go to the same switch and such.

Does a negative offset mean it is in the future? If so, I'm guessing I
need to dig and find an offset for cable delay (or similar)
in the TS2100? I seem to recall that the standard package came with 50'
or 150' of cable, but even that pre-factored delay wouldn't
equate to ~300-400us would it?



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