There are three options to Ethernet cable wiring: T568-A, T568-B, and cross-over. AT&T & other Telcos standardize on T568-A, where government entities opt for the latter T568-B. Therefore, residential and business contexts would mostly consist of T568-A. Moreover, common sense dictates that new wires should follow the existing layouts if it’s already been standardized in the building previously. Either wiring standard would work as long as both ends of the cables are consistent. The third option, cross-over, is only used to connect peer devices such as 2 computers or 2 network switches directly to one another.

Below is T568-A, also known as Straight-Through or Patch Cabling (where both ends are the same):

RJ45 Pin #

Wire Color
(T568A)

Wire Diagram
(T568A)

10Base-T Signal
100Base-TX Signal

1000Base-T Signal

1

Stripe Green

Transmit+

BI_DA+

2

Green

Transmit-

BI_DA-

3

Stripe Orange

Receive+

BI_DB+

4

Blue

Unused

BI_DC+

5

Stripe Blue

Unused

BI_DC-

6

Orange

Receive-

BI_DB-

7

Stripe Brown

Unused

BI_DD+

8

Brown

Unused

BI_DD-

Straight-Through Cable Pin Out for T568B:

RJ45 Pin #

Wire Color
(T568B)

Wire Diagram
(T568B)

10Base-T Signal
100Base-TX Signal

1000Base-T Signal

1

White/Orange

Transmit+

BI_DA+

2

Orange

Transmit-

BI_DA-

3

White/Green

Receive+

BI_DB+

4

Blue

Unused

BI_DC+

5

White/Blue

Unused

BI_DC-

6

Green

Receive-

BI_DB-

7

White/Brown

Unused

BI_DD+

8

Brown

Unused

BI_DD-

 

 

Crossover Wiring:

Although legacy telephone cables are less frequently used nowadays, to complete this document, here’s some information about RJ-11 wiring:

Usually the primary dial tone or talk circuit is wired to the center two pins (pins 3 & 4) and is the white/blue and blue/white pair (AKA: T1 & R1 – tip 1 and ring 1). A standard single line phone draws dial tone from these center pins.

NOTE: The type of wiring shown here is known as USOC (pronounced U-sock). See background below.

The multi-conductor cables attached to RJ11 connectors usually have colored sheaths.

position

RJ25 pin

RJ14 pin

RJ11 pin

Pair

T/R

±

Cat 5e/6 colors

Colors

Old colors

1

1

    

3

T

+

white/green

white/green

white

2

2

1

  

2

T

+

white/orange

white/orange

black

3

3

2

1

1

R

–

 blue

blue/white

red

4

4

3

2

1

T

+

white/blue

white/blue

green

5

5

4

  

2

R

–

 orange

orange/white

yellow

6

6

    

3

R

–

 green

green/white

blue
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