Origins
Cisco invented Cisco Inline Power on the year 2000. Switches were called Power Sourcing Equipments (PSE) and the devices which uses the power were called Powered Device (PD).
IEEE Brought Cisco Inline Power to an standard, PoE on 2003. it was called 802.af.
PoE Types
| Type | Standard Name | Name | Wattage | Year Released |
| Type 1 | PoE | 802.af | 15.4W | 2003 |
| Type 2 | PoE+ | 802.at | 30W | 2009 |
| Type 3 | 4PPoE | 802.bt | 60W | 2011 |
| Type 4 | 4PPoE | 802.bt | 90W | 2018 |
Active PoE
- Delivers only the power needed by the Devices
- Uses CDP or LLDP which stands for Cisco Discovery Protocol and Link Layer Discovery protocol respectively.
- Most Cisco switches supports both Discovery Protocols
Passive PoE
- Passive is Always-on Power
- Its mostly called 24VPoE
- Many Legacy equipments don't support CDP or LLDP
Device Classes
| Class | Standard | PSE Output | PD Input | PoE Type |
| Class 0 | 802.af | 15.4W | 12.94W | 1 |
| Class 1 | 802.af | 4W | 3.84W | 1 |
| Class 2 | 802.af | 7W | 6.49W | 1 |
| Class 3 | 802.af | 15.4W | 12.95W | 1 |
| Class 4 | 802.at | 30W | 25.5W | 2 |
| Class 5 | 802.bt | 45W | 40W | 3 |
| Class 5 | 802.bt | 60W | 51W | 3 |
| Class 5 | 802.bt | 75W | 62W | 4 |
| Class 5 | 802.bt | 90W | 73W | 4 |
If a device attempts to draw more power than the port configured to provide, a syslog message will be issued and the port will be shutdown and enter error-disabled state