Re: No matter where you go, there they are.

["Peter Trei" <trei@process.com>]

> 
> Peter - didn't they say that the checking station is also listening
> to the satellites?  That way they can tell that you are playing back
> signals that you taped earlier because they won't match what the
> satellites are broadcasting right now.
> 
> I think your idea would work if you wanted to pretend to be at a point
> which was _farther_ from each of the satellites than where you actually
> are.  Then you could delay all of the signals.  But the only way to
> be farther would be to be deep underground.  You might be able to pretend
> to be at the center of the earth, but that is not very useful.
> 
> Actually I suppose this only applies to those satellites which are shared
> between you and the checkin station.  If you are far away then maybe you
> only share one or two.  If you know which ones those are, you can lie to
> your heart's content about other ones, and for the shared ones you can
> again delay the signal and claim to be farther than you are.
> 
> If their authenticated repeaters are used then you have to assume the
> checking station has all the satellite signals and again the best you can
> do is pretend to be a Mole Man.
> 
> Hal

Denning hasn't thought this through. Do the math.

The diameter of the earth is 12,576 km
The speed of light is about 3e5 km/sec

-> max phase shift to simulate = 42 msec.

This is on roughly the same scale as network delays, or less. 

If you are trying to simulate a location in roughly the same area as your
actual location (say, on the same continent), the max phase shift to simulate is
a lot smaller - probably less than 5 ms.

The site checking the incoming packets for their origin has to allow for
realistic network delays - say 100 -200 ms.

Therefore any site that can see the same set of satellites as the site it is
trying to simulate can do so, buffering less than 50 ms of waveforms and
pretending to be on the end of a slow link.

Denning's plan: A beautiful idea murdered by cold, unfeeling facts.


 

Peter Trei
Senior Software Engineer
Purveyor Development Team                                
Process Software Corporation
http://www.process.com
trei@process.com