Which pairs of wires change termination order between the 568A and 568B standards?
- green and orange
- green and brown
- blue and brown
- brown and orange
The correct answer is:
- Green and orange
Introduction to the 568A and 568B Wiring Standards
The 568A and 568B standards refer to two different configurations of wiring in Ethernet cables, primarily used in Category 5e (Cat5e) and Category 6 (Cat6) twisted pair cables for network connectivity. These standards were established by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA) as part of the TIA/EIA-568 standards for commercial building cabling.
Both 568A and 568B standards specify how the eight wires (or four pairs) inside a twisted pair Ethernet cable should be terminated at the RJ45 connectors. These two wiring configurations differ in the arrangement of the color-coded wire pairs, but the cables function identically when terminated on both ends using the same standard. The only difference between the two standards is the termination order of the green and orange pairs.
Overview of the Wiring Pairs in an Ethernet Cable
An Ethernet cable contains eight individual wires grouped into four pairs. Each pair of wires is twisted together to minimize electromagnetic interference. The four pairs are color-coded for easy identification:
- Green pair: Green and white/green wires
- Orange pair: Orange and white/orange wires
- Blue pair: Blue and white/blue wires
- Brown pair: Brown and white/brown wires
These wires are terminated at an RJ45 connector, a standardized connector used for Ethernet connections. The RJ45 connectors are commonly used in both 568A and 568B standards, with the only difference being the arrangement of the green and orange pairs.
Difference Between the 568A and 568B Standards
The core difference between the 568A and 568B standards lies in the arrangement of the wires in the RJ45 connector. The position of the green and orange pairs is reversed between the two standards.
- 568A Standard:
- Pin 1: White/Green
- Pin 2: Green
- Pin 3: White/Orange
- Pin 4: Blue
- Pin 5: White/Blue
- Pin 6: Orange
- Pin 7: White/Brown
- Pin 8: Brown
- 568B Standard:
- Pin 1: White/Orange
- Pin 2: Orange
- Pin 3: White/Green
- Pin 4: Blue
- Pin 5: White/Blue
- Pin 6: Green
- Pin 7: White/Brown
- Pin 8: Brown
As you can see, the green and orange pairs are swapped between the two standards:
- In 568A, the green pair is terminated on pins 1 and 2, while the orange pair is terminated on pins 3 and 6.
- In 568B, the orange pair is terminated on pins 1 and 2, while the green pair is terminated on pins 3 and 6.
The blue and brown pairs, on the other hand, remain in the same positions across both standards:
- The blue pair is terminated on pins 4 and 5.
- The brown pair is terminated on pins 7 and 8.
Why Green and Orange Pairs Swap Between the Two Standards
The reason for the difference between the two standards is largely historical and based on the original development of Ethernet cabling. The 568A standard was developed first and was recommended for new installations as it is compatible with both voice and data networks. Later, the 568B standard became popular in the United States due to its compatibility with legacy telephone systems, which used the same wire pairing convention.
Though there is no functional difference between the two standards (as long as the same standard is used on both ends of the cable), the difference in the arrangement of the green and orange pairs is primarily due to differing historical usage conventions for voice and data networks. Both standards are fully compatible with modern Ethernet networks and are used interchangeably in different parts of the world.
Why the Green and Orange Pairs Matter
The green and orange pairs are significant because they are used for data transmission in 10BASE-T, 100BASE-TX, and 1000BASE-T Ethernet. Specifically, in 10/100 Mbps Ethernet, pins 1 and 2 (green pair in 568A, orange pair in 568B) are used for data transmission, while pins 3 and 6 (orange pair in 568A, green pair in 568B) are used for data reception.
In Gigabit Ethernet (1000BASE-T), all four pairs are used for bidirectional data transmission, which means that the entire cable is utilized for high-speed communication. However, even in Gigabit Ethernet, the placement of the green and orange pairs follows the same pattern for backward compatibility with 10/100 Mbps Ethernet.
Crossover Cables and the Role of the Green and Orange Pairs
When connecting two network devices of the same type, such as two computers or two switches, a crossover cable is often used. A crossover cable is terminated with the 568A standard on one end and the 568B standard on the other. The purpose of this crossover is to ensure that the transmit and receive signals are properly aligned between the two devices.
Since the green and orange pairs are reversed between 568A and 568B, a crossover cable effectively connects the transmit pins of one device to the receive pins of the other device, and vice versa. This makes the green and orange pairs particularly important in ensuring proper communication in such network setups.
In modern networking environments, many devices support auto-MDI/MDIX, a feature that automatically detects and corrects crossover issues, allowing straight-through cables to be used even in situations where a crossover cable would have been necessary. Nonetheless, understanding the role of the green and orange pairs in crossover cables is critical for older network devices or environments without auto-sensing capabilities.
The Irrelevance of the Blue and Brown Pairs in 10/100 Mbps Ethernet
It is worth noting that in 10BASE-T and 100BASE-TX Ethernet, the blue and brown pairs are not used for data transmission. These pairs are reserved for other uses, such as Power over Ethernet (PoE), which delivers electrical power over the Ethernet cable to power devices like IP cameras, phones, or wireless access points. Since these pairs do not change between the 568A and 568B standards, they are not directly relevant to the transmission of data in these Ethernet modes.
In contrast, in Gigabit Ethernet, all four pairs (green, orange, blue, and brown) are used, making the arrangement of all pairs important for high-speed data transmission.
Conclusion
In summary, the key difference between the 568A and 568B wiring standards lies in the termination of the green and orange pairs. These two pairs swap positions between the two standards:
- In 568A, the green pair is on pins 1 and 2, and the orange pair is on pins 3 and 6.
- In 568B, the orange pair is on pins 1 and 2, and the green pair is on pins 3 and 6.
This difference in wiring order is essential for ensuring compatibility in certain networking scenarios, especially when creating crossover cables or working with older Ethernet technologies. Understanding these standards and their wiring conventions is crucial for anyone involved in networking or IT infrastructure.