General principles for making RJ45 twisted‑pair cables:
Use one twisted‑pair for pins 1 and 2,
Use another twisted‑pair for pins 3 and 6,
The remaining wires can be connected arbitrarily as long as both cable ends are consistent.
For cables used for HUB uplink or direct PC‑to‑PC connection without a HUB,
keep one end unchanged, and swap the wire pairs of pins 1‑2 and 3‑6 on the other end.
The wiring color scheme adopted by professional network companies follows exactly the rules described above.
A twisted‑pair cable contains 8 conductors grouped into four twisted pairs:
Green is twisted with White‑Green, Blue with White‑Blue, and so on.
Notation used herein:
Metal contacts face upward, cable entry at the bottom; pin positions are numbered 1‑2‑3‑4‑5‑6‑7‑8 from left to right.
This refers to the well‑known 1‑2‑3‑6 wiring method.
Pins 1,2,3,6 are used for uplink and downlink data transmission: pins 1‑2 form one pair and pins 3‑6 form the other pair.
RJ45 twisted‑pair pin assignment:
1 Rx+
2 Rx‑
3 Tx+
6 Tx‑
Pins 4, 5, 7 and 8 are marked NA (Not Applicable).
Only assign one complete twisted‑pair to pins 1‑2,
and another complete twisted‑pair to pins 3‑6.
Remember: pins 1‑2 must use one twisted pair, pins 3‑6 must use a different twisted pair. Do not wire as 1‑2 for one pair, 3‑4 for the second pair, 5‑6 for the third pair, etc.
Improper wiring may work over short distances (some sources even claim up to 150 meters), and basic cable testers may report no faults.
However, it causes high bit‑error rates. Signal pairs (negative‑voltage signals) will travel over untwisted conductors,
resulting in severe near‑end crosstalk (NEXT).
Definition per TIA/EIA‑568A:
Metal contacts face upward, cable entry at the bottom; pin positions numbered 1‑2‑3‑4‑5‑6‑7‑8 from left to right.
1‑>White‑Orange ------------- 1‑>White‑Orange
2‑>Orange ------------- 2‑>Orange
3‑>White‑Green ------------- 3‑>White‑Green
4‑>Blue ------------- 4‑>Blue
5‑>White‑Blue ------------- 5‑>White‑Blue
6‑>Green ------------- 6‑>Green
7‑>White‑Brown ------------- 7‑>White‑Brown
8‑>Brown ------------- 8‑>Brown
---------------------------------------------------------------------
Crossover cables are used for HUB cascading or direct PC‑to‑PC connection without a HUB.
1‑>White‑Orange ------------- 1‑>White‑Green
2‑>Orange ------------- 2‑>Green
3‑>White‑Green ------------- 3‑>White‑Orange
4‑>Blue ------------- 4‑>Blue
5‑>White‑Blue ------------- 5‑>White‑Blue
6‑>Green ------------- 6‑>Orange
7‑>White‑Brown ------------- 7‑>White‑Brown
8‑>Brown ------------- 8‑>Brown
Simply swap the positions of wire pairs for pins 1‑2 and 3‑6!
