On Wed, 5 Apr 2006, Tim wrote:
On Tue, 2006-04-04 at 09:04 -0600, Robin Laing wrote:
As I understand it, the reason for the pair arrangement is based on
the older 4 pin phone connector and cross talk reduction between
pairs. This is described in the Google link provided by Ed Greshko.
Yeah, I read the article, but I still find it rather dubious how it
suggests that spreading the wires across the pins, will reduce crosstalk
significantly differently than just simply running the pairs next to
each other.
running the pairs next to each other wasn't really an option because
earlier connectors operate under the assumption that wires are paired
starting at the center and working out in either direction. using that
pattern for a 4 pair connector results in the outside one having wildly
different properties than the inside. so, by design the earlly assumption
holds true for the inside two pairs (3456) and the outside (12 and 78) are
simply paired.
rj45 has backward compatibility (with one pair/2 pair connectors) . as
does next generation gg45 (for 1 2 or 4) for 10Gb ethernet over twisted
pair.
With one of the pin outs, the one starting from the middle
and spreading outputs, seems that it'd be the worst possible
configuration, to me. Untwisting the pairs isn't a great way to reduce
crosstalk, nor would be overlapping half the pair across something else.
--
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Joel Jaeggli Unix Consulting joelja@xxxxxxxxxxxxxxxxxxxx
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