This article provides a comprehensive explanation of the core knowledge of the RJ45 interface (also known as an Ethernet network interface), covering the RJ45 wiring standard (T568A/T568B), RJ45 pin definitions, applicable scenarios, and best practices for engineering deployment. It helps network engineers quickly master the standardized use of the RJ45 interface and solve common problems in daily deployment and maintenance. It is an essential reference guide for enterprise network construction and low-voltage engineering.
According to IDC's 2025 Worldwide Network Equipment Market Report, the RJ45 interface, as the most widely used wired network interface, has annual shipments exceeding 23 billion units. It is widely used in enterprise networks, industrial control, smart homes, and other fields, and is a fundamental interface standard for modern network communication.
I. Basic Overview of the RJ45 Interface
The RJ45 interface (Ethernet interface) is the most commonly used wired network interface standard, typically used for data transmission. Its most common application is as a network interface card (NIC) interface, and it is the standard port in Fast Ethernet that uses twisted-pair cable as the transmission medium. The RJ45 connector, also known as a crystal head, has 8 pins and is widely used for connecting network cables (Category 5 cable or twisted-pair cable) between network devices in local area networks (LANs) and ADSL broadband internet access users.
RJ45 connectors come in two standards based on the wire sequence: one is green-white, green, orange-white, blue, blue-white, orange, brown-white, brown (T568A wiring); the other is orange-white, orange, green-white, blue, blue-white, green, brown-white, brown (T568B wiring). Correspondingly, network cables using RJ45 connectors are divided into straight-through cables and crossover cables.
II. RJ45 Wiring Standards and Classifications
1. T568A Wiring Standard
The RJ45 interface is the most commonly used wired network interface standard, typically used for data transmission. Its most common application is as a network interface card (NIC) interface, and it is the standard port in Fast Ethernet that uses twisted-pair cable as the transmission medium. The RJ45 connector, also known as a crystal head, has 8 pins and is widely used for connecting network cables (Category 5 or twisted-pair cables) between network devices in local area networks (LANs) and ADSL broadband internet access users.
RJ45 connectors come in two standards based on their wire sequence: one is green-white, green, orange-white, blue, blue-white, orange, brown-white, brown (T568A); the other is orange-white, orange, green-white, blue, blue-white, green, brown-white, brown (T568B). Corresponding network cables using RJ45 connectors are also divided into straight-through cables and crossover cables.
The pin correspondence between the T568A wiring sequence and the network cable colors is as follows: pin 1 green-white, pin 2 green, pin 3 orange-white, pin 4 blue, pin 5 blue-white, pin 6 orange, pin 7 brown-white, pin 8 brown. The T568A wiring sequence is suitable for crossover connections, where one end of the network cable uses the T568A wiring sequence and the other end uses the T568B wiring sequence.
2. T568B Wiring Standard
The pinout and color correspondence of the T568B wiring standard are as follows: Pin 1 orange-white, Pin 2 orange, Pin 3 green-white, Pin 4 blue, Pin 5 blue-white, Pin 6 green, Pin 7 brown-white, Pin 8 brown. T568B is currently the most commonly used wiring standard in engineering projects, supporting both straight-through (both ends are T568B) and crossover (one end T568B, one end T568A) wiring methods.
The pinout and color correspondence of the T568B wiring standard are as follows: Pin 1 orange-white, Pin 2 orange, Pin 3 green-white, Pin 4 blue, Pin 5 blue-white, Pin 6 green, Pin 7 brown-white, Pin 8 brown. T568B is currently the most commonly used wiring standard in engineering projects, supporting both straight-through (both ends are T568B) and crossover (one end T568B, one end T568A) wiring methods.
The correspondence between the pins of an RJ45 network cable connector and the color markings on the network cable is as follows: Pin Number | Network Cable Color 1 Orange White 2 Orange 3 Green White 4 Blue 5 Blue White 6 Green 7 Brown White 8 Brown
V. RJ45 Ethernet Interface FAQs
FAQ1: Are there differences in the RJ45 interfaces for Category 5, Category 5e, and Category 6 network cables?
A: The physical interface sizes are exactly the same. The main difference lies in the supported transmission performance. Category 5 cables support 100Mbps transmission, Category 5e supports 1000Mbps transmission, and Category 6 supports 10Gbps short-distance transmission. While the physical specifications of the corresponding RJ45 interfaces are the same, shielded interfaces offer stronger anti-interference capabilities and are more suitable for high-speed network environments.
FAQ2: What is the difference between shielded and unshielded RJ45 interfaces?
A: Shielded RJ45 interfaces have a metal shielding shell, effectively reducing electromagnetic interference and are suitable for industrial environments, areas with strong electromagnetic interference, or high-speed network deployments. Unshielded interfaces are less expensive and suitable for ordinary office and home environments with less interference.
FAQ3: What is the plug-in/plug-out lifespan of an RJ45 interface? A: Standard commercial-grade RJ45 interfaces have a plug-in/plug-out lifespan of at least 1000 cycles, while industrial-grade products can reach over 5000 cycles. Avoiding rough handling during daily use can effectively extend the interface's lifespan.
FAQ4: How to determine if an RJ45 interface is damaged?
A: Common symptoms include: intermittent network connection, identification as a 100Mbps network but unable to reach 1Gbps, a cable tester showing a non-continuity on a certain pin, and loose connector springs causing the network cable to easily detach. If any of these occur, it is recommended to replace the interface or re-crimp the RJ45 connector.
FAQ5: Are there differences in the RJ45 interfaces for Cat 5, Cat 5e, and Cat 6 network cables?
A: The physical interface sizes are exactly the same. The main difference lies in the supported transmission performance. Cat 5 supports 100Mbps transmission, Cat 5e supports 1000Mbps transmission, and Cat 6 supports 10Gbps short-distance transmission. While the physical specifications of the corresponding RJ45 interfaces are the same, shielded interfaces offer stronger anti-interference capabilities and are more suitable for high-speed network environments.
FAQ6: What is the difference between shielded and unshielded RJ45 interfaces?
A: Shielded RJ45 interfaces have a metal shielding shell, which effectively reduces electromagnetic interference and is suitable for industrial environments, areas with strong electromagnetic interference, or high-speed network deployments. Unshielded interfaces are less expensive and suitable for ordinary offices, homes, and other scenarios with less interference.
FAQ7: What is the insertion/removal lifespan of an RJ45 interface?
A: Standard commercial-grade RJ45 interfaces have an insertion/removal lifespan of no less than 1000 cycles, while industrial-grade products can reach over 5000 cycles. Avoiding rough handling during daily use can effectively extend the interface's lifespan.
FAQ8: How to determine if an RJ45 interface is damaged?
A: Common symptoms include: intermittent network connection, identification as a 100 Mbps network but unable to reach 1 Gbps, a cable tester showing a non-continuity on a certain pin, and loose connector springs causing the network cable to easily detach. If any of these issues occur, it is recommended to replace the interface or re-crimp the RJ45 connector.