Media Independent Interface
The term Media Independent Interface ( MII ) was introduced in Fast Ethernet for network components. It divides Fast Ethernet chipsets into two components: the Media Dependent Interface (MDI) and the MII. The interface between MII and MDI is a partial component of the Ethernet chipset and is identical for all manufacturers and all media (cables, fibers). The MDI, on the other hand, is the part of the chipset that has to be specifically designed for the respective medium (cable, fiber) (transceiver). It also includes the physical (electrical, optical) and mechanical interface between the Physical Medium Attachment (PMA) and the medium (cable). With classic 10 Mbit Ethernet, the interface between MII and MDI was also called AUI interface, the transceiver corresponds to the MDI, the rest of the card begins with the MII and ends at the respective system bus ( PCI , EISA , etc.).
The purpose of this distinction was to be able to produce chips with MII in large quantities, which are then supplemented by an MDI, which is also produced in large quantities across manufacturers. This enabled prices to be kept low. However, chipsets are also offered for network cards that no longer have MDI / MII interfaces.
The 10 Mbit predecessor is AUI , the Gigabit Ethernet variant is GMII ( Gigabit Media Independent Interface ).