How does the data flow with a Cat5e cable

Posted on 2012-09-12
Last Modified: 2013-11-12
Lets use a straight through cable:

1  transmit +
2  transmit -
3  receive +
4  unused
5  unused
6  receive -
7  unused
8  unused

So obviously transmit means that data is being sent and receiving means that data is being received.  

So why are two transmit wires needed and two receive wires needed?  

Also, if the Cat5e straight through cable is wired such that wires 1 & 2 are transmitting
and 3 & 6 are receiving, does this means that Ethernet switchports are configured like so:

1  receive +
2  receive -
3  transmit +
4  unused
5  unused
6  transmit -
7  unused
8  unused

I might have my + and - symbols in the wrong location on the second set of wires, because I'm not sure what they represent.

Question by:rotarypwr
    LVL 82

    Expert Comment

    by:Dave Baldwin
    There are two wires each for transmit and receive because they are transformer balanced, ungrounded, connections.  This is done to prevent ground loops between computers and network equipment.

    With old equipment, we used to have to cross-wire the cables to make sure the transmit and receive signals went to the correct pings.  Now, almost all computers and network gear use 'auto-sensing' ports that detect how the  signals need to be connected and do it automatically.
    LVL 82

    Accepted Solution


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