Re: Ethernet Crossover Cables

 Because there are two different standards. T4 uses all four pair, it's
designed for use with lower-quality cables. TX only uses two pair like
all other ethernet variants, but is supposed to be higher level cable.

HTH,

Scott Morris, CCIEx4 (R&S/ISP-Dial/Security/Service Provider) #4713,

JNCIE-M #153, JNCIS-ER, CISSP, et al.

JNCI-M, JNCI-ER

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Ivan Walker wrote:

  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

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Received on Wed Feb 03 2010 - 18:52:47 ART