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

    TX+ TX- RX+ RX-

    CCNA24968

      Hi all

       

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

       

      BUT

       

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

       

      Thanks

        • 1. Re: TX+ TX- RX+ RX-
          Conwyn

          HI CCNA

           

          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

          • 2. Re: TX+ TX- RX+ RX-
            CCNA24968

            Thanks Conwyn

             

            what if RX- is greater than RX+ ?

             

            Thanks

            • 3. Re: TX+ TX- RX+ RX-
              Ryan Ruckley CCNP

              Conwyn,

              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...