Power over Ethernet (PoE)

PoE allows Power Sourcing Equipment (PSE) to provice power to Powered Devices (PD) over an Ethernet cable.

Typically the PSE is a switch and the PDs are IP phones, IP cameras, wireless access points, etc.

The PSE receives AC power from the outlet, converts it to DC power, and supplies that DC power o the PDs.

Too much electrical current can damage electrical devices.

PoE has a process to determine if a connected device needs power, and how much power it needs.

• When a device is connected to a PoE-enabled port, the PSE (switch) sends low power signals, monitors the response, and determines how much power the PD needs.

• If the device needs power, the PSE supplies the power to allow the PD to boot.

• The PSE continues to monitor the PD and supply the required amount of power (but not too much!)

Power policing can be configured to prevent a PD from taking too much power.

• power inline police configures power policing with the default settings: disable the port and send a Syslog message if a PD draws too much power.

  • equivalent to power inline police action err-disable.

  • the interface will be put in an 'error-disabled' state and can be re-enabled with shutdown followed by no shutdown.

• power inline police action log does not shut down the interface if the PD draws too much power. It will restart the interface and send a Syslog message.

Standards

Name	Standard #	Watts	Powered Wire Pairs
Cisco Inline Power (ILP)
PoE (Type 1)
PoE+ (Type 2)
UPoE (Type 3)
UPoE (Type 4)