ethtool says that eth0 uses MII but twisted pair is used

Question

ethtool says that "Supported ports: [ TP MII ]" and "Port: MII". I guess that TP means twisted pair and Media Independent Interface. However physically I see that network card uses twisted pair cable, not this MII connector. So how can it be explained?

Solution

All modern Ethernet chips have the MAC built-in, and use a MII protocol over GMII, RGMII, or SerDes physical ports to communicate with the PHY device (even if it's built-in, this is usually true). If it's going to be a twisted pair interface, from the PHY the signal passes through a set of transformers and into the RJ-45 connection.

+-------+   +-------+   +-------+       +-------+    +-------+   +-------+
|       |   |       |   |       |       |       |    |       |   |       |
|Host   |<--+       |<--+       |<------+       |<---+       |<--+       |
|Ctrl   |   | FIFOs |   |  MAC  |  MII  |  PHY  |    |Xformer|   | RJ-45 |
|uC     +-->|       +-->|       +------>|       +--->|       +-->|       |
|       |   |       |   |       |       |       |    |       |   |       |
+-------+   +-------+   +-------+       +-------+    +-------+   +-------+