1. Overview of PoE Technology
Power over Ethernet (PoE), also known as Power over LAN (PoL) or Active Ethernet, enables Ethernet cables to transmit both data and electrical power simultaneously. This eliminates the need for separate power supplies, simplifying network deployment and maintenance.
A complete PoE system consists of two main components:
- PSE (Power Sourcing Equipment) – such as a PoE switch.
- PD (Powered Device) – such as a wireless AP or IoT LoRa gateway.
Both sides communicate based on IEEE standards to determine connection status, device type, and power level before power delivery begins.
2.IEEE 802.3af (PoE) Standard
2.1 System Characteristics
- Voltage range: 44–57V DC (typical 48V)
- Output power: up to 15.4W per port (PSE side)
- Available power for PD: up to 12.95W
- Current range: 10–350mA (normal operation), 350–500mA (overload protection)
2.2 Working Process
- Detection – PSE checks whether the connected device is PoE-compatible.
- Classification – PSE identifies the PD power class.
- Power On – Supplies 48V DC once validation is complete.
- Maintenance – Monitors load, detects faults or short circuits, and restarts when necessary.
2.3 Power Classification (IEEE 802.3af)
| Class | Power Range (PD) | Description |
| 0 | 0–12.95W | Default classification |
| 1 | 0–3.84W | Very low power |
| 2 | 3.85–6.49W | Low power |
| 3 | 6.5–12.95W | Standard PoE power |
3.IEEE 802.3at (PoE+)
To meet the demand for higher power devices, the IEEE 802.3at (PoE+) standard was introduced. It doubles the available power compared to PoE.
3.1 Key Parameters
- Voltage range: 50–57V DC
- Output power (PSE): up to 30W
- Power available for PD: up to 25–29.95W
- Supported Class: Class 4
Typical PDs include high-power access points, IP cameras, and VoIP phones.
4.IEEE 802.3bt (PoE++)
The IEEE 802.3bt standard—also known as PoE++—further expands PoE capabilities, introducing new power levels and enhanced features.
4.1 Key Enhancements
1.Increased power output:
PSE: up to 90W per port
PD: up to 71.3W
2.New power classes (Class 5–8):
Type 3: 40–60W
Type 4: 60–90W
3.4-pair power transmission:
Improves efficiency and supports higher data rates (2.5G/5G/10G Ethernet).
4.2 Backward Compatibility
IEEE 802.3bt is fully backward compatible with PoE (802.3af) and PoE+ (802.3at).
- A lower-power PD can safely connect to a higher-power PSE.
- A high-power PD can still function at a reduced power level when connected to a lower-power PSE.
5.Summary of PoE Power Levels
| Standard | Type | Power Class | PSE Max Output | PD Power | Voltage Range |
| IEEE 802.3af | Type 1 | Class 0–3 | 15.4W | 12.95W | 44–57V |
| IEEE 802.3at | Type 2 | Class 4 | 30W | 25–29.95W | 50–57V |
| IEEE 802.3bt | Type 3 | Class 5–6 | 60W | 51W | 50–57V |
| IEEE 802.3bt | Type 4 | Class 7–8 | 90W | 71.3W | 50–57V |
6.Application Scenarios
- PoE (802.3af): IP phones, standard Wi-Fi APs, small IP cameras
- PoE+ (802.3at): High-performance APs, PTZ cameras, video terminals
- PoE++ (802.3bt): Multi-channel APs, LED lighting systems, industrial gateways, digital signage
7.Advantages of PoE Technology
- Simplifies cabling and reduces installation cost
- Enables flexible deployment without separate power sources
- Enhances safety with overload and short-circuit protection
- Scalable from low to high power applications
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