POE IEEE 802.3af

IEEE 802.3af Overview

IEEE 802.3af, ratified in 2003, is an international standard that extends Ethernet technology to support Power over Ethernet (PoE). It enables simultaneous transmission of data and DC power over standard Ethernet cables (e.g., CAT5/CAT5e), eliminating the need for separate power supplies for connected devices47.

Key Features

1. 1.

   Power Delivery:

   • Provides up to 15.4W per port (with a minimum guaranteed power of 12.95W at the powered device)36.
   • Uses 48V DC power over twisted-pair Ethernet cables4.
2. 2.

   Device Compatibility:

   • Supports IP phones, wireless access points, network cameras, and other low-power devices14.
   • Backward-compatible with existing Ethernet infrastructure (no wiring modifications required)7.
3. 3.

   Safety & Classification:

   • Includes a classification mechanism (Class 0–4) to negotiate power requirements between Power Sourcing Equipment (PSE) and Powered Devices (PD)36.
   • Adheres to strict electrical safety standards to prevent cable overheating6.
4. 4.

   Limitations & Evolution:

   • Succeeded by IEEE 802.3at (PoE+), which delivers up to 30W to address higher-power applications like PTZ cameras and video phones6.

Significance

IEEE 802.3af revolutionized network deployments by simplifying installations, reducing costs, and enabling flexible device placement48. It remains foundational for PoE technology, though newer standards (e.g., 802.3bt) now support higher power levels.

For the full IEEE 802.3af-2003 specification, refer to the original document3