[ntp:questions] Clarification on the org, rec, xmt header fields

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Sat May 16 07:10:22 UTC 2009

>...and I'm curious about the timestamps.  I don't quite understand the
>values presented.  I've been pouring through the NTPv4 specification,
>but it doesn't provide a great deal of explanation.

If you assume a client-server model, from the client's view
there are 4 time stamps:
  when the request leaves the client
  when the request arrives at the server
  when the response leaves the server
  when the response arrives at the client

If you assume tha the network delays are symmetric,
you can figure out the network delay and clock offset
from those 4 numbers.

The key idea is that the server can twiddle it's thumbs
and do lots of crypto stuff and/or whatever else it
wants between the time the request arrives and the
time it sends the response.  That's why you need 4 time
stamps rather than only 3.

These are my opinions, not necessarily my employer's.  I hate spam.

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