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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