Attachment Unit Interface

The Attachment Unit Interface (AUI) is a physical and logical interface defined in the <a href="/facts/IEEE_802.3/Q9jxNSNT">IEEE 802.3</a> standard for <a href="/facts/10BASE5/vxgB15fH">10BASE5</a> Ethernet and the earlier <a href="/facts/Ethernet/nMfhU8tU">DIX standard</a>. The physical interface consists of a 15-pin <a href="/facts/D-subminiature/ygqtB3CQ">D-subminiature</a> connector that links an <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a> node's <a href="/facts/Physical_layer/WuATCrVw">physical signaling</a> to the <a href="/facts/Medium_Attachment_Unit/UHdofDhY">Medium Attachment Unit</a> (MAU), sometimes referred to as a <a href="/facts/Transceiver/S6HSzRPf">transceiver</a>. An AUI cable can extend up to 50 metres (160 feet), though often the MAU and <a href="/facts/Data_terminal_equipment/o7qvJVQq">data terminal equipment</a>'s (DTE) <a href="/facts/Medium_access_controller/hFpNzFFD">medium access controller</a> (MAC) are directly connected, bypassing the need for a cable. In Ethernet implementations where the DTE and MAU are combined, the AUI is typically omitted.
The IEEE 802.3 specification officially defines the AUI as an interconnect between a DTE and the MAU. However, devices like the <a href="/facts/Digital_Equipment_Corporation/ztxs6keA">DEC</a> <a href="/facts/Digital_Ethernet_Local_Network_Interconnect/9wnFzPvn">Digital Ethernet Local Network Interconnect</a> (DELNI) provided hub-like functionality using AUI-compatible connectors. Additionally, under certain conditions, it was possible to directly connect two AUI devices without the need for transceivers using a <a href="/facts/Crossover_cable/DSmnou6A">crossover cable</a>.
AUI connectors became increasingly rare in the early 1990s as computers and hubs directly integrated the MAU, especially with the rising adoption of the <a href="/facts/10BASE-T/2jRlgJb4">10BASE-T</a> standard. This shift led to the decline of <a href="/facts/10BASE5/vxgB15fH">10BASE5</a> (thicknet) and <a href="/facts/10BASE2/FfgUgSUz">10BASE2</a> (thinnet) which made use of the interface. The electrical AUI connection remained internally within equipment for some time.
With the introduction of <a href="/facts/Fast_Ethernet/YM5HjX0C">Fast Ethernet</a>, the AUI interface became obsolete and was replaced by the <a href="/facts/Media_Independent_Interface/CKB7edH3">Media Independent Interface</a> (MII). Subsequent Ethernet standards, such as <a href="/facts/Gigabit_Ethernet/1ItIoV2w">Gigabit Ethernet</a> and <a href="/facts/10_Gigabit_Ethernet/FvxUohpf">10 Gigabit Ethernet</a>, introduced the <a href="/facts/GMII/CKB7edH3">GMII</a> and <a href="/facts/XGMII/CKB7edH3">XGMII</a> interfaces, respectively. A 10 Gigabit Ethernet interface, known as <a href="/facts/XAUI/9wyTc2Yl">XAUI</a>, was developed to extend the operational distance of XGMII and reduce the number of interface signals.
A smaller variant called the <a href="/facts/Apple_Attachment_Unit_Interface/07N75RKb">Apple Attachment Unit Interface</a> (AAUI) was introduced on <a href="/facts/Apple_Macintosh/8GhnXTK0">Apple Macintosh</a> computers in 1991, and was phased out by 1998.

Attachment Unit Interface open-in-new

Attachment Unit Interface