Good evening, everyone!
In the wiring work, we often hear questions like "Should we use 568A or 568B?" and "What are the wire sequences of crossover cables and straight-through cables?".
Especially for new network colleagues, they are often confused:
"How exactly do we distinguish between A and B?"
"Is there still a need to use crossover cables now?"
"Can I just make a cable casually and it can still get the network connected. Does that mean it doesn't matter?"
Don't worry. In this article today, we will explain it all at once:
What are the wire sequences of twisted - pair 568A and 568B, what are the differences between them, and whether they are still needed now!
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1. What are 568A and 568B?
568A and 568B are two twisted - pair wire sequence standards defined by TIA/EIA (Telecommunications Industry Association). They are applicable to the connection methods of RJ45 network modular plugs.
There are a total of 8 wires in the twisted - pair cable, which are combined into wire pairs according to different colors and functions:
Check mark | Pair Name | Corresponding Color (568A) | Corresponding Color (568B) |
Pair 1 | Send data pairs | white-green / green | white-orange / orange |
Pair 2 | receive data pairs | white-orange / orange | white-green / green |
Pair 3 | Unused / Auxiliary | White and blue / Blue | White and blue / Blue |
Pair 4 | Unused / Auxiliary | White brown / Brown | White brown / Brown |
2. Wiring Sequence Diagrams of 568A and 568B (Practical Illustrations)
568A Wiring Sequence (left → right): 1: White/Green
2: Green
3: White/Orange
4: Blue
5: White/Blue
6: Orange
7: White/Brown
8: Brown
568B Wiring Sequence (left → right): 1: White/Orange
2: Orange
3: White/Green
4: Blue
5: White/Blue
6: Green
7: White/Brown
8: Brown
3. Straight-through Cable vs Cross-over Cable
Type | Wiring Sequence at Both Ends | Usage Scenarios |
Straight-through cable: | Both are 568A or 568B. | Connect a PC to a switch, an AP to a POE switch, etc. |
Crossed cable | One end is 568A, and the other end is 568B | PC to PC connection and switch to switch connection (without Auto-MDIX). |
4. Are crossover cables still in use nowadays?
Most modern switches and network interface cards support Auto-MDIX (Automatic Medium-Dependent Interface Crossover), which means:
"Whether it's a straight-through cable or a crossover cable, once plugged in, it can recognize and automatically adjust the transmission and reception directions."
Therefore, in most scenarios today:
• Straight-through cables are preferred, and the unified 568B standard is more common.
• Crossover cables are less common, but they may still be used in exams or with old devices.
5. Recommended Standards for Engineering Wiring
Project | Recommended Practices |
Engineering wiring | the 568B wiring sequence shall be uniformly adopted to facilitate later maintenance |
RJ45 connector making | Both ends should be wired with the same sequence (straight-through) |
10 Gigabit cabling | Use Category 5e/Category 6 or higher cables and match them with RJ45 connectors. |
Testing tools | Use a network tester to check the wire sequence and connectivity. |
6. Frequently Asked Questions and Answers
Q1: Why can I get the network connection even if I connect the two ends randomly?
A: Most devices support Auto - MDIX. However, this doesn't mean you can make the cable randomly! It is recommended to punch down the cable in a standardized way. Otherwise, it will be difficult to troubleshoot faults.
Q2: Why is 568B used uniformly in wiring projects?
A: 568B is more popular in North America and the Asia - Pacific region, which is convenient for unified management.
Q3: Can the 568B wire sequence be used for Cat5e and Cat6 network cables?
A: Of course. The wire sequence standard has nothing to do with the type of network cable.
Q4: How can I tell whether what I made is 568A or 568B?
A: Take a network cable, with the transparent RJ45 connector facing you and the clip facing down. Look at the colors from left to right:
• If the first pair is white - green/green, it is 568A.
• If the first pair is white - orange/orange, it is 568B.
If the wire sequences at both ends are the same, it is a straight - through cable; if they are different, it is a crossover cable.
That's all for today's sharing!
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