[ntp:questions] problem with synchronizing two comps to each other

Richard B. Gilbert rgilbert88 at comcast.net
Thu May 19 16:06:18 UTC 2005


Mike wrote:

> so you're telling, that it will be easier to update time from external 
> server? beacause I thought, that if 1 comp (master) keeps the time, 
> the other one (client) will adjust to it over LAN network. That it 
> will give beter results in setting the same time on both comps.
>
> I want to do that, because I want to measure the delay (latency) of 
> packet (the time between send and recieved). It's done by a software, 
> calleg mgen, which sends packets with timestamps, and then reciever 
> reads this timestamp, reads his own time, and puts them both into the 
> text file. The test should probably take about 24h max, so thats the 
> time i need these both computers to be synchronized with accurancy of 
> 1 ms, or maybe more, if there is no way in keeping 1ms accurancy.
>
> Or maybe you have other hint's how to measure the delay?
>
> Mike

Just how big a network latency are you trying to measure?  How 
accurately do you need to measure it?   On a LAN, delays are typically 
less than 500 microseconds.   To measure the transmission delay from 
machine A to machine B both clocks will need to be within considerably 
less than 500 microseconds.   Next, you are trying to synchronize the 
two machines using the same network you are trying to measure???  The 
uncertainty in transmitting time via NTP from one machine to another is 
one half of the round trip delay!

I think that you need to think a lot more carefully about what you are 
trying to do or at least describe it more carefully.



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