Some ethernet jacks come with the magnetics already in-built, saving you the trouble of including them yourself on the mounted-to PCB
The W5200 WIZnet. The single chip implements the PHY, the TCP/IP stack (fully hardwired), and the 10/100 MAC Ethernet MAC, in a QFN-48 package. It uses the SPI Protocol to talk to a microcontroller. It’s power save features include power-down mode and WOL (wake on LAN). It runs of 3.3V but has 5V I/O tolerance.