Medium Attachment Unit

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MAU is an acronym for Medium Attachment Unit, also known as "transceiver", which converts signals on an Ethernet cable to and from AUI signals.

On original 10base5 (Thick) Ethernet, the MAU was typically clamped to the Ethernet cable. With later standards (10base2 and later) it was generally integrated into the card and eventually as there was pressure to drive down costs the entire Ethernet controller was often integrated into a single chip. A MAU is similar to a hub, but allows for the passing of a token between the different network devices even though the network is a physical Star topology.

In most modern switched or hubbed Ethernet systems, neither the MAU nor the AUI interfaces exist (apart, perhaps as notional entities for the purposes of thinking about layering the interface), and the CAT5 cable connects directly into an Ethernet socket on the host or router. For backwards compatibility with equipment which still has external AUI interfaces, MAUs are still available with 10base2 or 10baseT connections.

However, the tradition of using a separate low-level I/O device in networking has continued in fast optical fiber network interfaces, where the GBIC, XPAK and XAUI interfaces play a similar role.