[ntp:questions] Garmin 18 LVC: whether to fudge

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Wed Feb 11 20:17:47 UTC 2009

shane-dated-1234940584 at csy.ca wrote:
>> Chris Adams wrote:
>>> Once upon a time, Richard B. Gilbert <rgilbert88 at comcast.net> said:
>>>> My bet would be that there is an asymmetry in your ADSL link!   If I'm
>>>> not mistaken, the "A" in ADSL stands for asymmetric!
>>> The asymmetry in ADSL is in bandwidth, not path or latency.  More
>>> frequency space is used for downstream (ISP->end user) communication
>>> than for upstream, but both travel the same path.
> Yeah, figured it was either interrupt latency or ADSL but thought ntpd might
> be able to factor the ADSL link out of the offset.  Is there any way I can
> do this manually?  As far as I could tell, fudge time1 only works for a
> refclock driver and not an internet server.

You are absolutely correct! :-)

I have wished for fudge time1 on network clocks for many years now, but 
I have realized that it will never happen unless I go in and write the 
code myself.

I know that Dave Mills prefers other solutions, in particular the 
huff-puff code which handles variable network congestion but cannot deal 
with a systematic/constant offset between send and receive paths.


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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