This paper assumes some knowledge of Ethernet, Cambridge Ring and token passing local area networks (LANs), and discusses the interfaces between LANs and attached devices. The emphasis is to some extent on hardware but mainly on the mapping of LAN protocol architectures onto physical realisations. Details for Ethernet and the Cambridge Ring in particular are described. An introduction is given to the notion of a transport box, in which software protocols up to and including the transport layer are built: this transport box consists of three logical parts, namely the network-dependent interface, the device-dependent interface, and the processor/memory unit in which the software resides.