[ntp:questions] Frequency adjustments in a local network

Maximilian Brehm maximilian.brehm at tu-ilmenau.de
Fri Apr 4 11:44:54 UTC 2014


Hey again,

thanks for the feedback so far. From your messages I realize I should
provide you with more information.
I would like to adjust the real time clock frequency of the destination
system. In the current setup the reference system has temperature
independent oscillators with a known drift (up to +/-2ppm) and the
destination system has standard computer oscillators (up to +/-100ppm).
The reference system supplies timestamps, however, they do not
reference
absolute time points but time points that are relative to the start of
the system. The destination's clock is synchronized via NTP over the
Internet and as mentioned incorrectly before, the destination system
needs the absolute time. In the current implementation, the timestamps
are already sent from the reference to the destination system for other
purposes and may be used for clock synchronization.
In a first approach (1), when the connection to the NTP servers
drops, the destination's clock should be adjusted based on the
reference
system's timestamps (but with the absolute time). In a second approach
(2), the NTP algorithm filter and adjustment algorithms should be
improved based on the reference system's timestamps.
The logic has to be implemented on the destination system using the
timestamps from the reference system. Do you think that a refclock
driver for (1) sufficient? And is there anything like (2) already
implemented or is a rewrite of NTP required? Do you have any general
ideas on either (1) or (2) or another one? PTP looks good but NTP is a
necessessity. 

Regards
Maximilian


Maximilian Brehm schrieb:
> Hey NTP community, 
> 
> I need to synchronize only the frequency of a
> destination systems based on the frequency of a reference system in the
> same network. This is because the reference system does not supply
> timestamps and they are not important for the destination system. So, I
> would say I need (a) only frequency and no clock adjustments for the
> destination system and (b) a method to synchronize clocks via a local
> network. 
> 
> Are there ways to achieve this using NTP that are implemented
> or may be implemented? If yes, can you recommend me starting points for
> either way? 
> 
> Thanks 
> 
> Maximilian Brehm
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