Ruigu Electronic

RJ-45, short for “Registered Jack 45,” is a standardized interface widely used for Ethernet network connections. With 8 pins, it is often referred to as an “8-pin modular connector.” It serves as a critical component for linking devices such as computers, routers, switches, and servers in modern wired networks. Here is a detailed explanation:

1. Physical Structure and Appearance

• Interface Form: Rectangular, typically made of plastic, with two types: “male connectors” (plugs, e.g., Ethernet cable connectors) and “female connectors” (ports, e.g., network ports on devices).
• Pin Configuration: 8 metal pins, numbered 1 to 8 (when the male plug is inserted, pins face upward from left to right as 1-8). Each pin corresponds to a copper wire in the Ethernet cable, facilitating electrical signal transmission.
• Mechanical Features: Equipped with a locking tab to secure the connection and prevent accidental disconnection. Some female ports include indicator lights (e.g., Link/Act LEDs) to display connection status and data transmission activity.

2. Working Principle and Applications

• Signal Transmission: Uses 8 copper wires (4 twisted pairs) in the Ethernet cable to transmit data via differential signaling. It supports various Ethernet speeds, including 10Mbps, 100Mbps, 1Gbps, and 10Gbps.
• Key Applications:
  • Connecting computers to routers or switches for local area network (LAN) access.
  • Wired interconnection between devices (e.g., switch cascading, server-to-storage connections).
  • Powering and communicating with industrial equipment or IP cameras via PoE (Power over Ethernet) through RJ-45 ports.

3. Ethernet Cables and Wiring Standards

RJ-45 interfaces require specific Ethernet cable specifications, with two common wiring standards:

1. T568A Standard:
   Pin 1-8 corresponds to wire colors: Green-White, Green, Orange-White, Blue, Blue-White, Orange, Brown-White, Brown.
2. T568B Standard (most widely used):
   Pin 1-8 corresponds to wire colors: Orange-White, Orange, Green-White, Blue, Blue-White, Green, Brown-White, Brown.

• Straight-Through vs. Crossover Cables:
  • Straight-Through Cables: Both ends use T568B (or both T568A), used for connecting different device types (e.g., computer to switch).
  • Crossover Cables: One end uses T568A, the other T568B. Historically used for connecting similar devices (e.g., computer to computer), but now rarely needed due to Auto-MDIX (automatic medium-dependent interface crossover) support in modern devices.

4. Differences from Other Interfaces

Interface Type	Number of Pins	Primary Use	Maximum Speed
RJ-45	8	Ethernet networks	100Gbps (with ultra-high-speed cables)
RJ-11	4/6	Telephone lines	Low-speed (voice or narrowband data only)

5. Evolution and Application Scenarios

• Speed Evolution: From early 10BASE-T (10Mbps) to modern Gigabit Ethernet (1Gbps), 10 Gigabit Ethernet (10Gbps), and even 40G/100G, RJ-45 interfaces continue to meet high-speed data transmission needs when paired with Cat5e, Cat6, Cat7, and higher-performance cables.
• Typical Scenarios: Home broadband router connections, enterprise LAN wiring, data center server clusters, and IP camera networks in surveillance systems.

With its standardization, high reliability, and flexible speed support, RJ-45 remains the dominant interface in global wired networks, playing a core role in network communication to this day.