An Attachment Unit Interface (AUI) is a 15 pin connection that provides a path between a node's Ethernet interface and the Medium Attachment Unit (MAU), sometimes known as a transceiver. It is the part of the IEEE Ethernet standard located between the Media Access Control (MAC), and the MAU. An AUI cable may be up to 50 meters long, although frequently the cable is omitted altogether and the MAU and MAC are directly attached to one another.