Wiring help?

[Joel Jaeggli]

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 at darkwing.uoregon.edu
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