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16792 Views 3 Replies Latest reply: Apr 11, 2010 10:28 PM by Ryan Ruckley CCNP RSS

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Apr 9, 2010 11:37 PM

CCNA24968 149 posts since
Mar 25, 2010

Hi all


I know TX+ TX- is Transmit & RX+ RX- is Receving




what exactly does TX+ and TX- means & how data is transmitted 



  • Conwyn 9,681 posts since
    Sep 10, 2008
    Currently Being Moderated
    1. Apr 9, 2010 11:48 PM (in response to CCNA24968)
    Re: TX+ TX- RX+ RX-



    We talk about 0 and 1     but often they are voltages. So what is zero and one.


    RX-   is the base voltage.  So by examine RX+  you can say does RX+ = RX-  then zero otherwise if RX+ is significantly greater than RX- then one.


    So the word significant means that RX- and RX+ are different enought not to be caused by natural electrical properities of the cables and connectors.


    Obviously it is a bit more complex than this.


    Regards Conwyn

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  • Ryan Ruckley CCNP 378 posts since
    Aug 26, 2009
    Currently Being Moderated
    3. Apr 11, 2010 10:28 PM (in response to Conwyn)
    Re: TX+ TX- RX+ RX-


    I had always thought that TX+ and TX- represented the differential pair that comprises the TX signal. Since all CAT5 etc cables are done in differential pairs this was how the individual signals are labelled.


    Thus TX+ is the exact opposite of TX-. The two combined will give you zero but fed into a differential amp and you have a signal. Thus noise induced on both cancels out whilst signal that is opposite on both carries through the amp.


    Does that sound right? Obviously same goes for RX. I guess I'm saying the same thing as you but from a different angle. My understading was that if TX+ == TX- then that didn't mean anything signal wise and that it was more like TX+ == 12V and TX- == -12V gives one symboll whilst , TX+ == -12V and TX- == +12V gives the other.


    Though my manchester encoding may be getting foggy...

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