What is T568B Wiring and T568A Wiring?
What is T568B and T568A?
T568B and T568A are two wiring standards established by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA). It is a standard that defines the ordering of the four twisted pairs of wires within ethernet cables.
How are the wiring colors for T568B and T568A?
T568B Wiring Colors Order (for an RJ45 connector, pins 1 to 8):
Orange/White
Orange
Green/White
Blue
Blue/White
Green
Brown/White
Brown.
T568A Wiring Colors Order (for an RJ45 connector, pins 1 to 8):
Green/White
Green
Orange/White
Blue
Blue/White
Orange
Brown/White
Brown.
Orange/White
Orange
Green/White
Blue
Blue/White
Green
Brown/White
Brown.
T568A Wiring Colors Order (for an RJ45 connector, pins 1 to 8):
Green/White
Green
Orange/White
Blue
Blue/White
Orange
Brown/White
Brown.
Which is more commonly used, T568A or T568B?
T568B is generally more commonly used than T568A.
Why T568B is generally more commonly used than T568A?
In the early days, network cards and switches did not support automatic port recognition and correction, so Ethernet cables were divided into straight-through and crossover types. A crossover cable used T568A on one end and T568B on the other, and was typically used to connect similar devices, such as computer to computer. A straight-through cable used the same standard on both ends—either T568A or T568B—and was used to connect different types of devices, like a computer to a hub.
Later, as switches and network cards began to support auto-MDI/MDI-X (automatic crossover), the need for crossover cables disappeared. As a result, T568A gradually faded from common use.
Why was T568A phased out rather than T568B?
Because T568B’s color order follows a light-to-dark sequence that’s easier to remember. More importantly, it offers better resistance to electromagnetic interference compared to T568A. In network installations, using a unified standard like T568B reduces confusion when multiple technicians are working simultaneously, and helps prevent wiring errors that are difficult to trace in large bundles. That’s why following the T568B standard is considered a safer and more reliable choice.
Later, as switches and network cards began to support auto-MDI/MDI-X (automatic crossover), the need for crossover cables disappeared. As a result, T568A gradually faded from common use.
Why was T568A phased out rather than T568B?
Because T568B’s color order follows a light-to-dark sequence that’s easier to remember. More importantly, it offers better resistance to electromagnetic interference compared to T568A. In network installations, using a unified standard like T568B reduces confusion when multiple technicians are working simultaneously, and helps prevent wiring errors that are difficult to trace in large bundles. That’s why following the T568B standard is considered a safer and more reliable choice.
What are the functions of the 8 cables in T568B?
In the T568B wiring standard, the 8 wires in a twisted pair Ethernet cable each serve specific roles in data transmission, especially for 10/100 Mbps Ethernet (Fast Ethernet) and Gigabit Ethernet (1000 Mbps).
For 10/100 Mbps Ethernet (using 2 pairs):
Pins 1 & 2 (White/Orange, Orange): Send data (TX)
Pins 3 & 6 (White/Green, Green): Receive data (RX)
Pins 4, 5, 7, 8: Unused (but still connected in the cable)
For Gigabit Ethernet (1000 Mbps, using all 4 pairs): All 8 pins are used.
Data is sent and received simultaneously on all four pairs (full-duplex, bi-directional).
For 10/100 Mbps Ethernet (using 2 pairs):
Pins 1 & 2 (White/Orange, Orange): Send data (TX)
Pins 3 & 6 (White/Green, Green): Receive data (RX)
Pins 4, 5, 7, 8: Unused (but still connected in the cable)
For Gigabit Ethernet (1000 Mbps, using all 4 pairs): All 8 pins are used.
Data is sent and received simultaneously on all four pairs (full-duplex, bi-directional).
How to choose T568A or T568B?
Choosing between T568A and T568B depends on your project requirements, compatibility needs, and regional or organizational standards.
Here are a few tips to help you decide：
✅ Choose T568A if:
You are working on residential or government projects in the U.S. (required by TIA/EIA standards).
You need to match existing T568A wiring in the building.
You're integrating with older telephone systems.
You need to match existing T568A wiring in the building.
You're integrating with older telephone systems.
✅ Choose T568B if:
You're doing commercial or business installations in the U.S.
The existing network uses T568B, and you want to maintain consistency.
You prefer easier memorization and slightly better resistance to interference (some installers claim this, though technically both perform the same).
The existing network uses T568B, and you want to maintain consistency.
You prefer easier memorization and slightly better resistance to interference (some installers claim this, though technically both perform the same).
Important Tips:
Always use the same standard on both ends of a cable (either A–A or B–B) for straight-through Ethernet cables.
Don’t mix standards unless you are intentionally making a crossover cable.
If you're unsure and not bound by specific requirements, T568B is the most commonly used standard today and is generally safe to follow for new installations.
Don’t mix standards unless you are intentionally making a crossover cable.
If you're unsure and not bound by specific requirements, T568B is the most commonly used standard today and is generally safe to follow for new installations.