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Re: Geo location to IP mapping

  • From: Marshall Eubanks
  • Date: Tue May 16 14:24:05 2006



On May 16, 2006, at 2:00 PM, Charles Cala wrote:


--- Marshall Eubanks <tme@multicasttech.com> wrote:

I seriously doubt this would work to better than the regional area.

My zip code (20124) region is about 5 km across, which would be 15
microseconds in vacuum, and
maybe at most 50 micro seconds in glass. So, you would need
accuracies at the 10's of microsecond level to specify zip codes.
don't forget, cable paths are not direct, and each bend in
the cable increases the distance that the light must
travel within the fiber. optical repeaters, optical
switches and other equipment can add distance,
(thus time) to the signal.

Please see
http://www.fiber-optics.info/fiber-history.htm

Oh, I am well aware of that, but you are making my point for me.

I have seen nothing to make me change my conclusion -

You can't do geolocation using network timing to much better than about 10 milliseconds because
you don't control either paths or the routers etc. in those paths. (This requires absolute timing;
differential measurements can be better and useful for some things, but they won't give you location.)

In glass, at 1/2 c, 10 msec is ~ 1500 km.

If you had an unlimited budget, lots and lots of measurement points with known locations, etc., and used other info (such as traceroutes) you might do a little better, but even a factor of ten better means 100 km error.

I am not saying you can't do geolocation, at least in some cases, but just that network timing won't get you anything very precise.

Regards
Marshall





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