What Is Classification?
We start by reacquainting ourselves with the basic handshaking overview presented in Fig. 3.3. After completing a successful detection, the PSE is now “sure” that there is an IEEE-compliant PD on the other end of the cable. It can then proceed to the next stage of the process: querying the PD as to its power requirement.
The process by which the PSE queries the PD as to its input power range is called classification. The PD in turn, declares its “class.” Alternatively put:
Classification is the process by which the PSE asks the PD: “How big are you (in terms of wattage)?” and the PD answers that question, akin to stating its size as indicated in Fig. 3.3.