Medium Independent Interface

The MII is an optional set of electronics that provides a way to link the Ethernet medium access control functions in the network device with the Physical Layer Device (PHY) that sends signals onto the network medium. An MII may optionally support both 10-Mbps and 100-Mbps operation, allowing suitably equipped network devices to connect to both 10BASE-T and 100BASE-T media segments.

The MII is designed to make the signalling differences among the various media segments transparent to the Ethernet chips in the network device. The MII converts the line signals received from the various media segments by the transceiver (PHY) into digital format signals that are then provided to the Ethernet chips in the device. The optional MII electronics, and associated 40-pin female connector and MII cable, makes it possible to connect a network device to any of several media types, providing maximum flexibility.

The MII electronics may be linked to an outboard transceiver through a 40-pin MII connector and a short MII cable. The MII cable for use with outboard 100-Mbps transceivers is specified as a 40-pin cable with a 40-pin plug on one end, equipped with male jack screws that screw into mating female screw locks. The cable can be a maximum of 0.5 meters in length (about 19.6 inches). It is also possible for the outboard transceiver to be attached directly to the MII connector on the device with no intervening cable, if the design of the transceiver allows it.

Quick Reference Guide to 100-Mbps Media Systems - 09 SEP 95

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