MII , GMII , RGMII

http://aca.cust.edu.tw/pub/journal/38/38-09.pdf
https://en.wikipedia.org/wiki/Media-independent_interface

The media-independent interface (MII) was originally defined as a standard interface used to connect a Fast Ethernet (i.e., 100 Mbit/s) media access control (MAC) block to a PHY chip. The MII design has been extended to support reduced signals and increased speeds.

基本上，這三個的作用是一樣的，同樣都是連結MAC層和PHY層的介面。區別在於編碼、速度、使用的腳位數、I/O clock的頻率不同。