TIA/EIA CAT 5 - T568A VS. T568B


Xmultiple's Engineering Department

What is the difference between the TIA/EIA standards 568-A and 568-B?

To explain the difference between T568A and T568B we need to look at some past history relevant to this standard.

The Computer Communications Industry Association requested that the Electronic Industries Alliance (EIA) develop standards for the cabling used in telecommunications applications back in 1985. This was the start of the standards.

The first revision of this standard was released in 1991, but was later updated again in 1995 due to the massive development of networking technology and new faster high-speed Ethernet cables and networking components. This was also replaced later with the current TIA/EIA 568-B standard.

Many aspects of networking structure and performance are addressed in these standards, the most visible and often misunderstood component is the definition of the wiring assignments in the RJ45 plug. A colored wire must be placed in a specific pin location in the plug in order for the cable to meet the standard. It is these wiring assignments that differ between the T568A and T568B standard.

The pins on the RJ45 plug are numbered 1 to 8. If you are holding a CAT 5 patch cable in your hand, as if inserting into a jack, with the contacts facing in the up position, pin 1 will be on the far left. Pin 8 will be the pin on the far right. This is the orientationused when defining the wiring assignments in the RJ45 plug.

CAT 5 Cable has four twisted pairs within the sheath. Each pair has a specific color code, and is to placed into deliberate pin location within the RJ45 plug. We will now identify the wiring locations in each of the standards:

TIA/EIA 568-A (T568A)

Pin 1 - white / green stripe

Pin 2 - green

Pin 3 - white / orange stripe

Pin 4 - blue

Pin 5 - white / blue stripe

pin 6 - orange

pin 7 - white / brown stripe

pin 8 - brown

TIA/EIA 568-B (T568B)

Pin 1 - white / orange stripe

Pin 2 - orange

Pin 3 - white / green stripe

Pin 4 - blue

Pin 5 - white / blue stripe

Pin 6 - green

Pin 7 - white / brown stripe

Pin 8 - brown

To make a crossover cable, you will construct the cable using the 568-A standard on one end, and the 568-B standard on the other. It is important to use the very best material that you can get in the construction of the cable, and that a top quality crimper is used as well. Make certain that the cable is checked using a test meter, to ensure that the wiring sequence is correct on each end. The 568-B standard is used in virtually every application in the United States, so make sure you discuss this before starting your project. In some cases, there may be special reasons to use the 568-A standard.


Is this answer helpful?