[ntp:questions] Re: Known asymmetry (DSL) compensation

David L. Mills mills at udel.edu
Tue Feb 15 22:58:47 UTC 2005


It would be nice to expand the fudge to non-refclocks, but this requires 
rewrite of the configuration code as well as changes in the remote 
configuration protocol. This in turn requires an asynchronous DNS 
implementation. Besides providing a broader fudge application, this 
would provide a really neat automatic pool capability. Nothing wildly 
difficulat about this, but really down and dirty. Previous broad hints 
for help in this area haven't raised any hands.


Mark Martinec wrote:
>>>I know it's not possible to know or compensate for all asymmetry in the
>>>packets between two machines.  However where there is a fixed, known,
>>>asymmetry - like on a DSL line shouldn't it be possible to calculate a
>>>fudge factor?
>>What you want to correct is the difference in latency in the upstream
>>vs. downstream directions. The trouble is that this cannot be readily
>>calculated from any known and constant values, such as the upstream
>>and downstream bitrates.
> I would very much like to see 'fudge time1' being applicable to
> network reference servers. Like John, I see a very predictive and
> stable offsets for network peers due to an asymmetric cable connection.
> Inability to correct for the systematic network offset forces
> one to either fudge local refclocks to wrong time, or declares
> networked references falsetickers.
>   Mark

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