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In planning an Ethernet network, the first choices you will make when laying cable are as follows. There are two cabling standards for Ethernet cables, the most common being T568A and T568B. While both standards serve the same purpose (connecting devices such as computers, routers, and switches via twisted-pair cables), the pinouts for the RJ45 connectors are different.
In this blog, we’ll analyze the differences between the T568A and T568B, discuss when to use both networks and answer some frequently asked questions to help you make the best choice for your network.
What Are T568A and T568B?
T568A and T568B are the Telecommunications Industry Association (TIA) cabling standards for Ethernet cables such as Cat5e or Cat6. These standards define the pinout of the eight wires of a twisted pair of Ethernet cables connected to an RJ45 connector.
Here’s a comparison of how the wire pairs are arranged in each standard:
| Pin Position | T568A Wire Color | T568B Wire Color |
|---|---|---|
| 1 | White/Green | White/Orange |
| 2 | Green | Orange |
| 3 | White/Orange | White/Green |
| 4 | Blue | Blue |
| 5 | White/Blue | White/Blue |
| 6 | Orange | Green |
| 7 | White/Brown | White/Brown |
| 8 | Brown | Brown |
As you can see, the main difference between the two is the order of the wire pairs. T568A starts with the green pair (Pin 1 and 2), while T568B begins with the orange pair (Pin 1 and 2).
Key Differences Between T568A and T568B
The most significant difference between T568A and T568B is the wire order. While both standards are functionally equivalent, the color-coded wiring sequence is different.
- T568A: The green pair comes first, followed by the orange pair.
- T568B: The orange pair comes first, followed by the green pair.
History and Usage
- T568A: This wiring standard was made to stay backwards-compatible with older telecommunications systems in the past (like, say), USOC (Universal Service Order Code) that was used for telephone wiring. T568A is still quite common in government buildings and older networks that need to work with phone systems.
- T568B: This is more common nowadays in commercial and residential work(especially for new installations) throughout the US. It maps to legacy 258A colour coding used by AT&T and became the de facto standard for new networks.
Which Wiring Standard Should You Use?
So, how do you choose between T568A and T568B? Well, it depends on a few factors:
1. Existing Network Setup
If you are expanding an existing network, follow the cabling standards being used. Using T568A with T568B may cause signal interference or slow download and upload speeds.
2. New Network Installation
T568B is usually the safer choice if starting over (this standard is more commonly used in the United States). T568A is acceptable for government facilities or networks that use older telephone systems.
3. Backward Compatibility
The T568A is preferred if compatibility with older telephone systems (USOC lines) is required; however, most modern network equipment supports both standards, so backward compatibility is no longer an issue today.
4. Network Performance
The good news is that both standards enable your network to perform equally well. However, you will get the same data speeds and performance if you configure only the T568A or T568B, with similar routing at both Ethernet cable ends. …… You will get the same data speeds and network reliability.
Straight-Through vs. Crossover Cables
In most cases, you will use straight-through cables to connect devices such as a computer to a router or a switch to a router. These cables are wired the same way at both ends, either T568A or T568B.
However, crossover cables connect similar devices (such as a computer to a computer or a switch to a switch). Crossover cables use the T568A on one end and the T568B on the other to “crossover” the transmit and receive pairs to establish the correct connection.
But here’s a helpful hint: Most modern network devices now support Auto MDI-X, which automatically detects and adjusts the connection type. This means that crossover cables are not as necessary as they once were!
How to Identify T568A vs. T568B
Want to know which cabling standard your Ethernet cable uses? It’s easy to tell by visually inspecting the RJ45 connector:
- T568A: The first pair of wires is white/green and green.
- T568B: The first pair of cables is white/orange and orange.
In addition, you can check the wiring sequence with a cable tester.
Frequently Asked Questions (FAQ)
What’s the difference between T568A and T568B?
The main difference is the order in which the pairs are arranged; the T568A places the green pairs in positions 1 and 2, while the T568B places the orange pairs in both positions.
Can I mix T568A and T568B in the same network?
Mixing the two standards in the same network is not recommended, as it can cause connection problems. However, you can use both standards in crossover cables designed to connect similar devices.
Which standard is more commonly used in the US?
T568B is more widely used in commercial and residential networks in the US, while T568A is typically used in legacy systems, government facilities, and specific specialized applications.
Do T568A and T568B affect network performance?
No, the performance of both standards is the same. The only difference is the wiring order, but as long as the wiring is the same at both ends, it will not affect the network’s speed or reliability.
Conclusion
Choosing between T568A and T568B is not complicated. The key is consistency, i.e., ensuring that both ends of the Ethernet cable follow the same cabling standards. If you are working with an existing network, stick with the standards you already have. T568B is a solid choice for most modern setups if you start from scratch.
Remember, both standards have the same performance, so as long as you stay consistent, your network will run smoothly and efficiently.
Apple Liu, Romtronic’s Marketing Manager, specializes in driving Asian market growth. With a degree in International English and eight years of sales experience in the electronic cable and harness industry, she brings deep industry expertise and a global perspective. She is passionate about Romtronic’s leadership in digital engineering and is dedicated to advancing the brand’s presence and innovation.
