[time-nuts] clock-block any need ?

Hal Murray hmurray at megapathdsl.net
Sat Dec 29 03:18:06 UTC 2012


attila at kinali.ch said:
> From the data ntp gives me in the networks i manage. I hardly get any
> jitter number below 1ms, even with unloaded network and unloaded hosts. The
> 200us comes from the "usual" rtt time measurements on PCs. 

What sort of networks are you talking about?  Are you synchronizing over LAN 
or WAN?  Do you have a local refclock?

On LANs with non-ancient PCs, it's easy to get round trip times under 200 
usec.  That makes it hard to get jitter over 1 ms.  Or, if the jitter is that 
bad, how can you call the network unloaded?

Here are a couple of ntpq printouts:

$ ntpq -p tim
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*glypnod         .PPS.            1 u  194  256  377    0.145    0.186   0.018
-shuksan         .PPS.            1 u   95  256  377    0.115    0.126   0.030
-mini-mon        .PPS.            1 u   68  256  377    0.177    0.080   0.030
-tom             192.168.1.3      2 u   57  256  377    0.200    0.161   0.086
+bob             .PPS.            1 u  117  256  377    0.146    0.199   0.045
+ted             .PPS.            1 u   11  256  377    0.211    0.208   0.036

$ ntpq -p tom
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*glypnod         .PPS.            1 u   37  256  377    0.130    0.043   0.014
-shuksan         .PPS.            1 u   91  256  377    0.139   -0.005   0.015
+mini-mon        .PPS.            1 u  191  256  377    0.172   -0.006   0.023
-bob             .PPS.            1 u  198  256  377    0.392    0.186   0.050
+ted             .PPS.            1 u  206  256  377    0.319    0.127   0.038
-tim             192.168.1.3      2 u   34  256  377    0.243   -0.074   0.036
-jim             199.102.46.72    2 u   31  256  377   26.243    8.357  29.291
-xo-c2           155.101.3.113    3 u  126  256  377   28.335   10.815  23.143

The last two lines are from systems synchronizing out over the 
big-bad-internet.  The others systems are all local to my LAN.  (Calling it a 
LAN is stretching things.  It's just one switch.)



-- 
These are my opinions.  I hate spam.






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