ARINC Characteristic 765 defines an Ethernet Switch Unit (ESU), which fits in the general architectural philosophy and aircraft infrastructure for the proper use and interface of various information network related equipment. This document specifies an ESU intended for various aircraft information network related equipment. It provides a wired network connection among the connected devices based on interfaces defined by ARINC Specification 664 and IEEE 802.3 CSMA/CD (Ethernet).