Medium Attachment Unit

Two Medium Attachment Units, or transceivers. (The units shown are backwards compatibility-oriented 10BASET MAUs, not the more typical 10BASE5 MAUs; cf. article.)

A Medium Attachment Unit (MAU) is a transceiver which converts signals on an Ethernet cable to and from Attachment Unit Interface (AUI) signals.

On original 10BASE5 (Thick) Ethernet, the MAU was typically clamped to the Ethernet cable. With later standards it was generally integrated into the network interface controller and eventually the entire Ethernet controller was often integrated into a single integrated circuit ("chip") to reduce cost.

In most modern switched or hubbed Ethernet over twisted pair 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 category 5 (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.

The following standard, Fast Ethernet introduces division onto Media Access Controller (MAC) and Physical Layer Interface (PHY) layers connected with Media Independent Interface (MII). Some early Fast Ethernet hardware had a physical external MII connectors, functionally similar to AUI connector. 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, XENPAK, XFP, and enhanced small form-factor pluggable (SFP+) pluggable transceiver modules using the XAUI interface play a similar role.

Objectives of MAU:

MAU Characteristics:

Services provided by MAU:

Two modes of operation:

MAU functional specifications:

MAU in this context is not to be confused with a Media Access Unit, which shares the same acronym.