Networking Guide : Cat 5 Wiring Scheme

EIA and TIA have produced many cable standards that are widely used in telecommunication and networking. The one that is often referred to in networking lessons is EIA/TIA-568 that's Commercial Building Telecommunications Cabling Standard.

EIA/TIA-568 is the basis for Cat 5 cable wiring scheme. Wires inside a Cat 5 cable are color-coded. There are four pairs of copper wires, but only two pairs are used for transmit and receive. The pair and pin designation for Cat5 cable is defined in EIA/TIA-568A and EIA/TIA-568B. 568A is the original standard which later is updated by 568B. The difference between 568A and 568B is clearly illustrated in the table below.

  568A 568B
Pair Wire Pin Wire Pin
1 White/Blue 5 White/Blue 5
  Blue 4 Blue 4
2 White/Orange 3 White/Orange 1
  Orange 6 Orange 2
3 White/Green 1 White/Green 3
  Green 2 Green 6
4 White/Brown 7 White/Brown 7
  Brown 8 Brown 8

Table: 568A vs. 568B
Pin and pair designation in two EIA/TIA standards.
This applies to Cat 5, Cat 5e, and Cat 6 cables.

The difference between 568A and 568B wiring scheme is in pair 2 and pair 3. In 568A, pin 3 (white/orange) and pin 6 (orange) combine in pair 2 while pin 1 (white/green) and pin 2 (green) in pair 3. In 568B, pin 1 (white/orange) and pin 2 (orange) combine in pair 2 while pin 3 (white/green) and pin 6 (green) in pair 3. Either 568A or 568B wiring scheme can be chosen but it must be used consistently throughout a network.

page 2 : straight-through cable vs. crossover cable
page 3 : RJ-45 connector pins and crimping tool

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