Ethernet Crossover Cables

Wikipedia has a detailed explanation of crossover cables here
http://en.wikipedia.org/wiki/Ethernet_crossover_cable#Crossover_cable_pinouts

covering the pins outs for 1000Base-T and 100Base-TX. 1000Base-T
crossover cables cross all four pairs where as 100Base-TX crossover cables
cross only 2 pairs (can cross four but only 2 pairs are used anyway).

Looking at some crossover cables I found I did indeed find some with all
pairs crossed and some with only 2 pairs crossed. When testing these in
some Cisco switches both worked fine at 1Gps. This was kind of unexpected
as I anticipated that the crossover with only 2 pairs crossed would not
work.

I tried disabling mdix and speed/duplex negiation etc but could not break
it. Can anyone explain why a crossover cable with only 2 pairs crossed
still works for 1000Base-T.

Cheers

Ivan

Blogs and organic groups at http://www.ccie.net
Received on Thu Feb 04 2010 - 12:35:53 ART