[ntp:questions] ntpdate function

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Wed Apr 10 21:08:22 UTC 2013

Jacek Igalson wrote:
> 1. Could you be more specific about code comparison, please

Compare the source code for the applications you are getting the data from.
  What are the differences in timestamp (system time) acquisition?
  What are the differences in when / where packets are time stamped?
  What are the differences in how the latency is calculated?


> 2. ntpdate can be used with option -p, 1 to 8 sampling.
>    Difference of delay is 0.05586 sec to 0.05359 sec.
>    Result from ntpq is 28 msec.
>    To big to be a statistical explanation

You are comparing the ping Average, to the ntpdate delay?


 ping -n 8 ntp.example.net
   Minimum = 82ms, Maximum = 84ms, Average = 83ms


 ntpdate -4 -q -v -p 8 ntp.example.net
  server, stratum 1, offset -0.015873, delay 0.10370

 ICMP echo may have a lower priority than NTP;

 Ping and NTP may be taking the time from different places
  in the platform / OS, and/or with different function calls;
   {e.g. one at reception of packet in network adapter,
     another at user application level}

 Ping may be calculating the round trip time
  differently than ntpdate delay;


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