[Edinburgh-pm] Happy Birthday Television
perl at aaroncrane.co.uk
Sun Jan 23 09:04:14 PST 2011
A Smith <asmith9983 at gmail.com> wrote:
> We can discuss whether this 20th century television thing about to be
> totally superceded by sending the signal via the Internet rather than
> through the Ether. It does mean that Mars Man won't be able to watch it,
> unless he has a ultra-sensitive WiFi receiver.
Not even then. The distance between us and Mars is never less than
about 54 gigametres, and goes up to 400 Gm or so. The speed of light
is 1.8e12 furlongs per fortnight, or just shy of 300 Mm per second.
So the distance to Mars is in the range 180..1334 light seconds, and
therefore the minimum transmission time to Mars is 180..1334 seconds.
However, RFC 793 specifies a Maximum Segment Lifetime for TCP of 120
seconds; no TCP segment is permitted to be "active" in the
internetwork for more than 120 seconds. So, by definition, we can't
do TCP to Mars. :-)
Aaron Crane ** http://aaroncrane.co.uk/
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