A communication protocol called “FlexRay” (trademark of Daimler Chrysler AG) is known as a type of protocol for a communication network system installed in a vehicle. FlexRay realizes a communication speed of a maximum of approximately 10 Mbps (megabits per second) while ensuring high reliability. FlexRay has attracted attention as an important technology for practicing electronic control (X-by-wire) of a portion related to vehicle running.
In FlexRay, a time trigger method is employed as a data transfer method, and frame transmission timing and frame receiving timing of each of nodes on a network are scheduled beforehand. In FlexRay, so-called “communication cycles” are used. One communication cycle defines a static segment in which each slot that is a time interval for transmitting a frame has a fixed length, and a dynamic segment in which each slot has a variable length. In FlexRay, each node on the network recognizes timing of each slot assigned to the node in the static segment and dynamic segment in each communication cycle in accordance with a global time that is common time recognition in the network, and that node transmits a frame to be transmitted to a different node in the slot. In addition, the node recognizes timing of each slot assigned for transmitting a frame to be received by the node and receives a frame transmitted from the different node in the slot. When each node on the network receives the frame transmitted from the different node, the node acquires reception status information representing a frame reception state in the slot, and, on the basis of the reception status information, checks whether to normally receive the frame.