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Networking Fundamentals · Foundational

Power over Ethernet (PoE)

Delivering DC power and data together over twisted-pair Ethernet cabling, standardized in IEEE 802.3af, 802.3at and 802.3bt.

Definition

PoE powers access points, IP phones, cameras and IoT devices without separate electrical outlets. The original 802.3af provides up to 15.4 W at the source (12.95 W at the device). The switch detects a valid device signature before applying power and allocates power from its PoE budget.

Example

An IP phone powers up from the switch port with no power adapter.

Exam tip

Watch the switch's total PoE budget; enough ports does not mean enough watts.

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