Power Over Ethernet Interoperability Guide

Types of Classification Methods and Backward Compatibility

Keep in mind that the handshaking process presented in Fig. 3.3 is just exemplary. And it is just one possibility within the broad category of classification. The category is characterized by the use of small currents and voltages for signaling across the copper wire (quite similar to the detection process). Copper is the “physical layer” (or medium) here, and is also called layer 1 or just L1. So this method is generically referred to as physical-layer classification or layer-1 classification or L1 classification. It was the original classification method used in the AF standard.

There is also a very different category of classification based on querying the PD’s power rating over ...