Re: How to calculate the offset of your local time against an NTP reference server

[martin]

The Reference Timestamp is the time at which the server clock was last set or corrected. That does not tell anything about the local clock offset.

In order to guess the local clock offset an SNTP client has to evaluate four timestamps:

t1 = local clock, time request sent by client;
t2 = server clock, time request received by server;
t3 = server clock, time reply sent by server;
t4 = local clock, time reply received by client

The offset o is then calculated as:

o = ((t2 - t1) + (t3 - t4)) / 2

Net::NTP will save you the trouble of doing this explicitly and give you the offset right away. It will also not suffer additional inaccuracy from the delay between your gettimeofday() and get_ntp_response() calls.

[thanos1983]

Hello Martin,

Thank you for your time and effort reading my question and replying. I was afraid that I was so wrong when I also read the RFC4330 where it explains the way it should it should be calculated.

As you mentioned I do not really need to calculate the offset since I can use the Net::NTP module. The reason that I need to use it is I am planning to apply this process on several remote OS through SSH, where I will not be able to have the NET::NTP module available.

Again thank you for your feedback it is really valuable to me to contineou with my experimentation.

[SuicideJunkie]

If you can run your own script, then you can use Net::NTP

It is pure perl, with only core dependencies.

[thanos1983]

Hello SuicideJunkie,

Thank you for your time and effort reading and replying to my question.

You mean I run my script into an external the same script?