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T568a vs T568b Termination

T568a vs T568b Termination

Ethernet is still the backbone of modern networking. It shows up all the time, and there’s a good chance that you regularly work with Ethernet devices.

Considering that, it’s important to know a little bit about Ethernet and how it works, and one important topic covers the little connectors that actually allow you to plug in an Ethernet cable.

Those connectors are called cable terminations, since that’s where each cable ends.

What you might not know is that a single Ethernet cable can be connected in different ways, and there are two internationally recognized and used standards to determine how you terminate an Ethernet cable. Those standards are T568a and T568b, and if you don’t know the differences, it could create problems in your network.

What Are These Terminations?

In both cases, we’re referring to Ethernet cable terminations. T568a is the first of the two to be standardized and recognized. As such, it’s backward compatible with some older systems. Meanwhile, T568b is the newer standard and much more popular in modern networks.

What are these standards and what do they mean?

Well, the standards define the orientation of wire pairs within the termination of an Ethernet cable. If you have ever crimped your own cable, the standard determines what order the different colored wires should follow.

If you haven’t crimped your own wires, the standards arrange the little wires inside of the plastic clip you use to plug in an Ethernet cable.

Here’s the thing. Both standards are Ethernet, and both work. In fact, you can even have both termination types in the same network (with caveats that will be discussed). The big thing is that a single wire can’t switch from one termination to the other. So, if one end of a cable uses the “B” termination, the other end can’t use the “A” termination.

This gets a little more complicated when you think about networking infrastructure. If you’re designing a network, you might run Ethernet through the walls and put jacks in spots where you want to connect equipment. Even though there are multiple wires and junctions in that infrastructure, everything needs to run on the same termination. If you switch from one to the other, you’re destroying the alignment of the wire pairs that carry signals, and that creates problems.

When we say that both terminations can be used in the same network, that’s only possible when they are separated by signal processing. As an example, you could terminate with A into a fiber optics switch. That switch connects to another via a fiber cable. The second switch could then connect to new devices on B, and there would be no problem. This is because the signal has been converted away from Ethernet and back again, so the termination configuration ceases to matter.

If no signal conversion takes place, you can’t mix and match these terminations.


  1. White Green
  2. Green
  3. White Orange
  4. Blue
  5. White Blue
  6. Orange
  7. White Brown
  8. Brown

This configuration is partly backward compatible with USOC wiring, which only matters when connecting to very old devices. Still, that’s worth noting.


  1. White Orange
  2. Orange
  3. White Green
  4. Blue
  5. White Blue
  6. Green
  7. White Brown
  8. Brown

This configuration matches the AT&T 258A color code, and that’s why it’s the more popular option in modern networks.

When to Use Each Termination

That covers all of the significant differences between these two terminations. So, which should you use?

In a vacuum, it doesn’t matter. They offer identical performance in terms of Ethernet connectivity. That said, the popularity of B is worth noting. Because it is so much more popular, you’re more likely to find it to be the configuration in pre-terminated cables. In fact, every pre-terminated Ethernet cable carried by Cables and Kits follows the B standard.

So, unless you specifically need A, it’s probably safer to stick with B. One situation where you might need A is with specific government contracts that require it.

Ultimately, what matters most is that you stay consistent with your choice. As long as you do that, your network will work just fine.

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