Relay connection unit and vehicle-mounted communication system

摘要

A Relay connection unit connects networks connected to ECUs via multiple communication lines and relays signals transmitted/received between the ECUs belonging to the different networks. The relay connection unit comprises a recording part that records the relationship between ECUs that currently transmit/receive signals to/from each other; a buffer part that records transmission completion times at which the relay connection unit transmits signals received from ECUs to the networks to which other ECUs of relay destination belong; and a communication abnormality determining part that determine a time difference (T) between the transmission completion time corresponding to a network, for which the signal transmission has been completed the earliest, and each of the transmission completion times corresponding to the other networks for which signal transmissions have been completed and that determines that the signal transmission to a network for which the corresponding time difference is equal to or greater than a predetermined time is a communication delay.