Inline Power and PoE are used to provide power to IP phones, wireless access points etc. by the catalyst switch trough the same data cable.
In the reality, as you may know, out of 8 channels in the UTP cable, only 4 is used for data transmission. So these methods use the rest to provide power to the devices. 
Cisco Provides 3 methods to deliver current through the Ethernet cable:
- Cisco Inline Power
- 802.3af PoE
- 802.3at PoE+
| Property | Inline Power | 802.3af | 802.3at PoE+ |
| Standard | Cisco Proprietary | IEEE standard | IEEE standard |
| Maximum power delivery | 7W/port | 15.4W/port | 34.20 W |
| Cable speed | 10/100 only | Compatible with gigabit Ethernet | Compatible with gigabit Ethernet |
| Compatibility | Incompatible with all non-Cisco devices that accept power over Ethernet | Not compatible with Cisco inline power – the power negotiation process is completely different | Backward compatible with 802.3af |
The devices connecting to the port are divided into different classes depending up on the power consumption:
| Class | Max Power | |
| 0 | 15.4 W | Default |
| 1 | 4.0 W | |
| 2 | 7.0 W | |
| 3 | 15.4 W | |
| 4 | Undefined | Future Use |
Some advantages of using these methods are:
- Centralized point of power
- Centralized point of backup
- Cheaper cabling
Configuration
Switch#show power inline ;to see the current status of ports
Switch(config-if)#power inline {auto|never|delay}
- auto: automatically detect power
- never: to disable power supply through that port
- delay: wait up to the given delay time before turning off the power of that port if the phone went offline. This is useful when phone is rebooting.
Switch(config-if)#power inline {consumption mw | static max mw} ;to give power specifically
Note: We don’t need to type any command. Cisco switch detect all cisco devices and power needed by the devices automatically using CDP.
