Re: ATM (was Re: too many routes)

[Geoff Huston <gih () telstra net>]

Photons propagate at 0.65c in fibre - the exact speed does vary
depending on whether its single or multimode fibre.  As I
dimly recall single mode fibre is every so slightly faster.

The equivalent EMR propagation speed in coppr is 0.75c

And the EMR propagation speed in a vacuum is c (and according
to Einstein it doesn't matter how fast you are travelling at
the time.)

Of course this assumes that anyone wants to know... Quite
frankly I was having a good time listening to everyone blame
thost nasty horrible slow routers for the missing 30ms. :-)


   Geoff



At 08:05 PM 9/11/97 -0700, Vadim Antonov wrote:
> 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
> nonsense.
>
> --vadim