[ntp:questions] On flakeways, scattergrams and timequakes

David L. Mills mills at udel.edu
Thu Jan 24 19:59:43 UTC 2008


Danny,

Your comment on another thread about weather modelling stirred my pot. I 
gave a long thought about modelling when designing the synthetic sources 
for the ntpd simulator. With the Allan characteristic in mind the 
synthetic sources use exponentially distributed phase noise plus 
random-walk frequency noise, which nicely models the Allan 
characteristic shown in my papers and others.

But, that's kid's stuff. The real ornery cases can't be explained this 
easily. The best examples I have were when ARPAnet was operating really 
  badly, but nobody knew why. It turned out routes were flapping between 
landline and satellite paths, as confirmed by the NTP rawstats wedge 
scattergrams. The scattergrams showed four overlapping wedges, each 
corresponding to one possible combination of landline and satellite 
links  on each direction.

Another interesting case was the early Internet path via the Atlanic to 
Italy, which had frequent glorious flaps over one second. For that 
matter the huff-n'-puff data shown in das Buch are wonderful grist for 
the NTP mill.

Once upon a time earlly in Internet times Bob Braden at UCLA operated a 
"flakeway" best described as a route deflector that scattered incoming 
packets to random destinations. It was used as for testing TCP and 
routing algorithms. We need a similar package that can operate as an NTP 
server and do various kinds of timequakes for testing.

Dave




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