Ring, star, trunk and drop, and daisy chain Bus refers to a concept for cabling devices together, part of a family of connection topologies that also includes the ring and star. The bus topology uses a main trunk cable that connects all devices linearly. the devices connect to the trunk using drop lines, the bus is called trunk and drop, such as thick Ethernet, Modbus+, AB+, ControlNet, and Proxox DH-II. If the devices connect directly onto the trunk with no drop lines, the bus is a daisy chain, such as thin Ethernet, Genius I/O, and ProfiBus-DP. Some buses, such as DeviceNet and Foundation fieldbus H1, can be either.