ISO 17458-4:2013 specifies the electrical physical layer for FlexRay communications systems.
The electrical physical layer for FlexRay is designed for time-triggered networks with data-rates up to 10 Mbit/s to connect automotive electronic control units (ECUs). The medium that is used is dual wires. Signalling on the bus is accomplished by asserting a differential voltage between those wires. Topology variations range from point-to-point connections via linear passive busses and passive stars up to active star topologies.
ISO 17458-4:2013 includes the definition of electrical characteristics of the transmission itself and also documentation of basic functionality for bus driver (BD) and active star (AS) devices.