Patent ID: 8255109

Claim:
A relay connection unit, mounted on a vehicle, which is interposed between networks connected with electronic control units via communication lines and which relays data signals transmitted and received between said electronic control units belonging to different networks of said networks, comprising: a reception part that receives a data signal from one of said electronic control units; a transmission part that transmits, from the relay connection unit, the data signal received from the one of said electronic control units to others of said electronic control units belonging to said different networks respectively; a buffer part that records points in time at which transmissions of said data signal, to said different networks to which others of said electronic control units belong respectively, are completed, such that a plurality of points in time are recorded, each point in time relating to a respective one of the electronic control units; and a communication abnormality determining part that uses the points in time recorded by said buffer part to find a plurality of time differences, each time difference being a difference between (i) an earliest one of the points in time and (ii) another one of the points in time, and for each time difference determines that if said time difference is not less than a specified time, a communication delay has occurred in said transmission of said data signals.