[ntp:questions] Frequently asked question about error bounds?

berra.84 berra.84 at spray.se
Mon Nov 2 15:33:14 UTC 2009


Thanks for your answers. Yes the RFC-1305 is obselete, but they are
using it for the servers where I work right now. The problem just now
is to figure out why a SNTP(RFC2030)-client aren't able to synchronize
to a NTP-server with RFC-1305.

I agree with you that the second alternative must be a simplification
of the first. The simplification states that if delay is much bigger
than dispersion you get the interval
I = [offset - delay/2, offset + delay/2]
____

With these commands beneath I get status from my server. I can't
figure out how it produced the synchronization distance to 1.312 for
stratum 2. In RFC-1305 this expression is stated:
sync dist = root.dispersion + root delay/2

And for last, how can root delay be lower than delay for server
xx.xx.xx.x2 ?
The same is true for the stratum 3 syncronizaion source, root delay
0.93 msec, delay 5.66 msec.


drnlulerout1a#show ntp status

Clock is synchronized, stratum 2, reference is xx.xx.xx.x2
nominal freq is 250.0000 Hz, actual freq is 249.9983 Hz, precision is
2**18
reference time is CE7EDE35.4C5E87C6 (13:08:37.298 GMT+1 Tue Oct 13
2009)
clock offset is 0.0160 msec, root delay is 0.66 msec
root dispersion is 0.17 msec, peer dispersion is 0.06 msec


#show ntp associations

      address         ref clock     st  when  poll reach  delay
offset    disp
+~xx.xx.xx.x1      .GPS.             1     0    64  377    23.1
0.05     0.5
*~xx.xx.xx.x2       .GPS.             1    55    64  377     0.7
0.02     0.1
+~xx.xx.xx.x3      .GPS.             1    46    64  377    14.2
0.15     0.1
 * master (synced), # master (unsynced), + selected, - candidate, ~
configured

#show ntp associations detail

xx.xx.xx.x2   configured, our_master, sane, valid, stratum 1
ref ID .GPS., time CE7EDE35.4C49BA5F (13:08:37.297 GMT+1 Tue Oct 13
2009)
our mode client, peer mode server, our poll intvl 64, peer poll intvl
64
root delay 0.00 msec, root disp 0.09, reach 377, sync dist 1.312
delay 0.66 msec, offset 0.0160 msec, dispersion 0.06
precision 2**16, version 3
org time CE7EDE35.4C49BA5F (13:08:37.297 GMT+1 Tue Oct 13 2009)
rcv time CE7EDE35.4C5E87C6 (13:08:37.298 GMT+1 Tue Oct 13 2009)
xmt time CE7EDE35.306647D9 (13:08:37.189 GMT+1 Tue Oct 13 2009)
filtdelay =     0.66    0.93    0.66    0.64    1.05    0.76
0.85    0.69
filtoffset =    0.02   -0.00   -0.02   -0.01    0.29    0.04   -0.07
-0.01
filterror =     0.02    0.99    1.97    2.94    3.92    4.90
5.87    6.85


Thanks for your sharing your competence
B




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