Inline Power / Power over Ethernet (PoE)

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:

1. Cisco Inline Power
2. 802.3af PoE
3. 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.