Re: IMAP needs 100T

From: Fielder George Dowding <fgdowding@iceworm-enterprises.net>
Date: Mon Dec 25 2006 - 13:07:30 AKST

Lee wrote:
> Ummmm...there's this new-fangled thing out now called 1000BaseT...?
> (insert smiley here)
>
> Beste Holiday Wishes to all
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Talk about "new-fangled"... Go easy on me, I could understand pushing a
signal having a 10mc (MHz) bandwidth through RG58 given it being
terminated at both ends with its characteristic impedance and using high
impedance taps along its length, but doing the same thing over
unshielded twisted pair --- huh! Obviously not possible.

I remember the story of the engineers (c. 1880) who doubted one could
transmit power to distant points over a transmission line because the
maximum power transfer theorem required equal resistance at generator
and load. Obviously, the generator would burn up! The solution was to
use a constant voltage distribution system, minimize the losses
(resistance factor) in the generator, and never even thing about
approaching the maximum power transfer point.

So, having seen this stuff work, I still haven't wrapped my mind around
the concept. I do note the twist in old POTS house wire was about one
turn per foot, CAT3 (new house wire) seems to have about 6 turns per
foot, and CAT5(x) is somewhere around 12 turns per foot = one turn per
inch. All this improves the bandwidth to the detriment of the velocity
factor. The losses increase which is one of the limits of the allowable
distance between active devices (NIC, router, switch, etc). Another
factor which limits the distance between active devices is the increase
in distributed inductance and capacitance because of the higher rate of
turns. This is an area where I have little real understanding. I will
have to (someday) look at the maths behind the theory.

One of the things which advance the speed has been the signal coding
techniques. Back in my undergraduate days, I was interested in
Information Theory, but it got too mathematical for me and I wasn't (at
the time) interested in coding, compression, etc. I first noted the
improvement in analog modems and I tried to figure out what coding
techniques were being used, again because obviously, pumping 28.8kbs
over a POTS line having a design bandwidth of a mere 4kHz was impossible
 (the minimum bandwidth required without clever coding for a 28.8kbs
signal would be about 15kHz). Ha, well the joke is on me.

Awaiting hand-me-down 1000T stuff without 'bated breath.

-- 
Mit freundlichen Grüßen / Best regards       Debian/GNU Linux
Fielder George Dowding, Chief Iceworm        "etch" Testing
dba Iceworm Enterprises, Anchorage, Alaska   User Number 269482
Since 1976 - Over 30 Years of Service.       "irad" 301256
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Received on Mon Dec 25 13:06:42 2006

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