[ntp:questions] Getting NTP to correct only the clock skew

Hans Jørgen Jakobsen hjj at wheel.dk
Fri Apr 6 10:05:22 UTC 2007

On Thu, 05 Apr 2007 21:53:16 +0200, Spoon wrote:
> Hans Jørgen Jakobsen wrote:
>> Spoon wrote:
>> The master(A) send packets out at its rate.
>> B answers trying to have N in the buffer.
> This was my original implementation. It did not work well.

Did you have a buffer large enough to take care of jitter.

>> Could you change the protocol and allow to flag that a packet is going
>> to be dropped or send a dummy answer?
> Could you expand on this suggestion?
> What is the purpose of the flag?

When buffer full drop an answer to A.
To be kind to A, B tell A that a packet will be missing. Either
piggyback in previous packet or as seperate packet.

When buffer is empty. Send packet with no or dummy data.

You could have a flag with values "normal data",
normal data but dropping next packet","no data cause buffer empty".
Or "normal data","no data cause buffer full","no data cause buffer empty"

As mentioned by others this looks as a flow control problem.

What are the requirements between A and B. Do there have to be a 1:1
number of packets. How do you handle droped packet (You did use UDP!)
How important is timing? Its important to A? to B? to A and B?
Is the rate that packets flow important? to A? to B? to A and B?

>> Sending packet at a smooth rate of 1000 Hz requires a fairly accurate
>> scheduling.
> I'm running a soft real-time OS with high-resolution timers.
> A frequency of 1 kHz is easy to achieve.

Also schedule something to happen every 1.001 milisecond?

>> (In telecom they have the same problem. Their solution involves systems
>> of frequency synchronized clocks)
> What is a frequency synchronized clock?
Sorry, didnt use the right words. Should be "frequency disciplined oscillator".

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