First-generation data transmission in a vehicle required that every input and output signal had to be allocated an individual conductor; that meant a dedicated wire and terminals. This was necessary because binary signals can only be transmitted using binary “on” or “off” states. On/off ratios worked fine to transmit continually changing values such as the status of an accelerator pedal-travel sensor. As data exchange volumes between controllers increased over the years, it no longer made sense to handle communications by conventional hard wire and plug-in connectors. Each module shown requires a direct connection to any other module it has to communicate with. It is a modification on a star network. In more recent systems, the objective is to keep wiring-harness complexity down to a minimum to reduce both costs and technical malfunctions. For this we use a serial data bus described a little later in this section.