To connect a node to the wire, an Auxiliary Unit Interface (AUI) is used from the node to a transceiver. The transceiver is attached directly to the wire.
Internetworking with Cisco and Microsoft technologies, pg. 228
Even the smallest LAN technically has a backbone, which could be any of the 4 basic topology types. Any time you need to connect various routers, switches, etc., together you connect them via a...