Wed 14 June 2017
A standard ethernet cable (Cat 5, CAT 5E, or Cat 6) has 4 pairs of cables (8 wires total). For 10BaseT (10Mbps) and 100BaseT (100Mbps) they only use 2 pairs of wires:
|1||White with Green||+TD|
|3||White with Orange||+RD|
|5||White with Blue||Not Used|
|7||White with Brown||Not Used|
From the table above, you can see that 10/100BaseT only uses the Green and Orange twisted pairs of wires. Where TD and RD are transmit and receive. The +/- is an inverted polarity system to reduce noise and increase performance. Basically, if +TD is at +5V, then -TD is at 0V. This mirroring, helps to reduce reduce noise effects that could drown out a normal signal over long distances.
Now for 1000BaseT, it operates the same way, but gigabit uses all 4 pairs (8 wires) to communicate.