**First, Power over Ethernet Technology**
Power over Ethernet (PoE) is a technology that allows the delivery of both electrical power and data signals through a single Ethernet cable. This innovation enables IP-based devices such as IP phones, wireless access points, and security cameras to receive power without the need for separate power cords. By utilizing existing Ethernet infrastructure, PoE simplifies installation, reduces costs, and enhances flexibility in network design. The system transmits DC power alongside data signals over twisted-pair cables, ensuring safe and efficient operation. The IEEE 802.3af standard was introduced to define how power is delivered over Ethernet, making it a widely adopted protocol in modern networking environments. Unlike traditional data protocols, PoE primarily focuses on power delivery while maintaining compatibility with standard data communication.
**Second, the Structure and Principle of the Ethernet Power Supply System**
2.1 **Components of a PoE System**
A complete PoE system consists of two main components: the Power Sourcing Equipment (PSE) and the Powered Device (PD). The PSE is responsible for injecting power into the Ethernet cable and managing the distribution of power across connected devices. On the other hand, the PD is the device that receives both power and data, such as an IP phone or a surveillance camera. Before delivering power, the PSE performs a detection process to identify whether the connected device supports PoE. This ensures that power is only supplied to compatible devices, preventing damage to non-PoE equipment.
2.2 **Power Transmission Modes**
The IEEE 802.3af standard outlines two primary methods of power delivery: **Endspan PSE** and **Midspan PSE**.
- **Endspan PSE**: This type of PSE integrates power delivery directly into network switches or routers. It provides power through the same Ethernet cable used for data transmission, typically using pairs 1, 2, 3, and 6 in the twisted-pair cable. Endspan PSEs are commonly found in switches that support PoE, such as those used in enterprise and small business networks. They can supply up to 48V DC and support various Ethernet standards, including 10BASE-T, 100BASE-TX, and 1000BASE-T.
- **Midspan PSE**: A midspan PSE is a separate device placed between the switch and the PD. It injects power into the Ethernet line without interfering with the data signal. Midspan PSEs are often used when the existing switch does not support PoE. These devices typically have two RJ45 ports—one connected to the switch and the other to the PD. Midspan PSEs usually deliver power through the unused wire pairs (pairs 4, 5, 7, and 8), which do not carry data. They are limited to supporting 10BASE-T and 100BASE-TX networks, as per the 802.3af standard.
By combining power and data delivery, PoE has revolutionized the way networked devices are powered, offering greater efficiency, reliability, and cost savings in a wide range of applications.
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