ATM (was Re: too many routes)

Vadim Antonov avg at
Fri Sep 12 03:05:13 UTC 1997

Richard Irving wrote:

>  Light can travel around the world 8 times in 1 second. This means it
> can travel
> once around the world (full trip) in ~ 120 ms. Milliseconds, not
> micro....

You've got faster light than anybody else.  The speed of light
is about 300000 km/s _in vacuum_; that gives 134 ms arond the 
planet's equator.

> So, why does one trip across North america take 70ms...

a) light is slower in dense media
b) fibers are not laid out in straight lines  (in fact, i saw
   a circuit going from Seattle to Vancouver via Fort Worth :)

70 ms RTT = 35 ms one way.  Given that U.S. is about 50 deg. wide,
it is abput 0.7ms/degree; or 250 ms around the world.

Less than 2 times slower than light in vacuum.

> Hint, it is not the speed of light. Time is incurred encoding, 
> decoding, and routing.

Hint: have a look at a telco's fiber map before spreading


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