CCNA Power over Ethernet

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PoE Standards

PoE is used to power devices like phones, cameras, and wireless access points, from a switch port. This eliminates the need for separate power sockets in the wall for each of these devices.

Any device that supplies PoE power is called a PSE (Power Sourcing Equipment)

PoE started with Cisco Inline Power around 20 years ago. This delivered 7 watts of power per switch port. This was a good idea, so IEEE created their own version (which became PoE).

The original PoE (which is still in use) is 802.3af, and can deliver 15.4W per port. This is good for small devices and appliances.

Additional standards have been released to supply more power for bigger devices:

  • PoE+ 802.3at (type 2) – 30W
  • PoE++ 802.3bt (type 3) – 60W
  • PoE++ 802.3bt (type 4) – 100W


Supplying Power

The switch is one type of PSE, but we can also use PoE injectors. These are devices that are connected to external power, and inject power into the network cable, alongside the data. These are useful if you don’t have a PoE capable switch.

The opposite of this is the PoE splitter. This takes power and data on one cable, and splits them, so we have power and data on two separate cables.

Each switch has a PoE budget, which is the total amount of power it can supply. Each device that consumes power subtracts the maximum potential power draw from this budget.