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

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


Mark,

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.

Dave

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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