There are multiple standardized PoE types which deliver varying levels of power in different ways. These types are based on IEEE standards.
- Type 1 - IEEE 802.3af
- Type 2 - 802.3at
- Type 3 and 4 - 802.3bt
There are also different PoE classes that range from class 0 to class 8. These define how much power should be sent to a device, ranging from 4 to 99 watts.
- Type 1 specifies four classes
- Type 2 specifies a single class
- Types 3 and 4 specify an additional four classes
Standardized PoE involves an initial negotiation between the powered device (PD), say an IP phone, and the power sourcing equipment (PSE), such as a PoE switch. The PD requests specific PoE requirements, and if the PSE supports those requirements, it delivers the requested power.
Standards-based PoE guarantees operation at up to 100 meters of CAT5 or CAT6 cable, the same distance that Ethernet is certified to function.
For non-standardized PoE, take a look at Passive PoE