PoE without Ag9120-S

Guys!!! I read some data sheet and documents of the PoE. I have a question about making PoE without Ag9120-S module. If I use voltage step-down module to level the voltage down to 5v~7v, can I make my board to do Arduino PoE project ?

The AG9600 series is compatible with IEEE 802.3af Power-over-Ethernet (PoE) standard. You should probably implement that standard. For an introduction, see: http://www.ieee.li/pdf/viewgraphs/introduction_to_poe_ieee802.3af_802.3at.pdf

In the name of IEEE Standard, I accept it and thank you so much, John :)