[time-nuts] Project on precise timing over Ethernet

Magnus Danielson magnus at rubidium.dyndns.org
Fri Sep 11 07:36:53 UTC 2009

Javier Serrano wrote:
> Yes, exchanging data over a link will always harm its timing
> accuracy/precision performance, irrespective of whether you steer clocks
> (our case) or you exchange values or both. In fact, as I said to Jeremy in
> another thread I tend to see clock steering (i.e. PLL) as a limit case of
> interchanging values, where this exchange would happen at every single clock
> tick. So you end up with lots more information, up to you to low-pass filter
> to get rid of high frequency phase noise.

Actually, you can see this as a Shannon information channel, analog or 
digital. The produced information is the phase difference between the 
master and slave oscillator, but it may be encoded digitally over other 
clocks. However, since the information capacity is never properly 
estimated the long term phase information quality can vary alot. The 
systematic noise sources added is also almost never properly analyzed.

Ah well.


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