How To Make An RJ45 Straight Through And Cross-Over Cable

COLOR-CODE STANDARDS

Again, please bear with me…  Let’s start with simple pin-out diagrams of the two types of UTP Ethernet cables and watch how committees can make a can of worms out of them.  Here are the diagrams:

 image001.gif

 

Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus and minus to minus.  And that  you must use a crossover cable to connect units with identical interfaces.  If you use a straight-through cable, one of the two units must, in effect, perform the cross-over function.

Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B. The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):

 image003.gif      image002.gif

If we apply the 568A color code and show all eight wires, our pin-out looks like this:

image004.gif

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard.  Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing–they are just plain wasted.

However, the actual cables are not physically that simple.  In the diagrams, the orange pair of wires are not adjacent.  The blue pair is upside-down.  The right ends match RJ-45 jacks and the left ends do not.  If, for example, we invert the left side of the 568A “straight”-thru cable to match a 568A jack–put one 180° twist in the entire cable from end-to-end–and twist together and rearrange the appropriate pairs, we get the following can-of-worms:

image0051.gif

This further emphasizes, I hope,  the importance of the word “twist” in making network cables which will work.  You cannot use an flat-untwisted telephone cable for a network cable.  Furthermore, you must use a pair of twisted wires to connect a set of transmitter pins to their corresponding receiver pins.  You cannot use a wire from one pair and another wire from a different pair.

Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by untwisting  the wires, except the 180° twist in the entire cable, and bending the ends upward.  Likewise, if we exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable.  If we cross the green and orange pairs in the 568A diagram we will arrive at a simplified diagram for a crossover cable.  All three are shown below.
image006.gif

12 Comments

  1. Comment by Dennis Kevin on September 29, 2010 9:49 am

    I’ve gone through your notes for assistance and I must say that your notes are good, short,simplified and easy to understand.I’m assisted and very grateful.
    Thanks alot!

  2. Comment by Dennis Kevin on September 29, 2010 9:55 am

    I’ve gone through your notes for assistance and I must say that your notes are good, short,simplified and easy to understand.I’m assisted and very grateful.
    Thanks alot!

  3. Comment by Dennis Kevin on September 29, 2010 9:57 am

    I’ve gone through your notes for assistance and I must say that your notes are good, short,simplified and easy to understand.I’m assisted and very grateful.

    Thanks alot!

  4. Comment by ReMonica Richardson on December 1, 2010 4:13 pm

    How do you keep the wires straight so you don’t have open pins and crossed wires.

  5. Comment by benedicta yeboah on March 20, 2012 3:02 pm

    send me news leaf every day

  6. Comment by Kashif Christi on July 20, 2012 7:01 am

    i want to say thanks to all probby for support us ..thanks you too much dears

  7. Comment by nandramsharma on August 30, 2012 10:16 am

    CCNA,MCSE,A+,N+

  8. Comment by amith.p on September 17, 2012 10:24 am

    this information are very interesting , and more use full.

  9. Comment by diaz guntur febrian on November 17, 2012 10:06 am

    Nice Explaination .. :)

  10. Comment by miya on November 26, 2012 8:52 am

    thanks for info.

  11. Comment by ARAMIDE on December 10, 2012 9:32 am

    a job well done.

  12. Comment by krishnakumar on December 17, 2012 6:07 pm

    rj 45 cross conection which colour

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