PoE lets you send both data and power over a single Ethernet cable. Commonly used for access points, IP cameras and VoIP phones.

• 2 types of PoE : Active and Passive
• Active = smart. It negotiates power safely
• Passive = dumb. It just sends the power
• Easy, cheap and fast deployment
• Switch → PSE (Power Sourcing Equipment)
• PD → Powered Device
• 802.3at = very common

First big standard was 802.3af (15.4 watts per port). That's Type 1 PoE.

A very common standard is 802.3at aka PoE+ (30 watts per port). That's Type 2 PoE.

Later, Cisco introduced UPOE (Type 3, up to 60 watts per port) then IEEE standardized higher-power PoE with 802.3bt (Type 4, up to 90 watts).

Most of the time, these standards are backward compatible.

The PSE and the PD talk to each other to negotiate the necessary power. The negotiation may use protocols such as:

• CDP (Cisco Discovery Protocol)
• LLDP (Link Layer Discovery Protocol)

• Ethernet
• OSI - TCP/IP