Patent ID: 7948998

Claim:
A Local Area Network (LAN) system mounted on a vehicle comprising a plurality of LANs, mounted on said vehicle, each having at least one electronic control unit connected with a communication line to send and receive messages; and a relay connection unit, connected with said communication line, for relaying said messages between said LANs mounted on said vehicle, wherein each electronic control unit has a reception port having a function of sending a reception confirmation signal to said relay connection unit in response to a received message; and said relay connection unit has a relay management means for judging whether relay is necessary according to whether said reception confirmation signal has been sent in response to said message relayed to each of said LANs mounted on said vehicle, and updating relay processing information stored in a storing means, wherein when said relay management means of said relay connection unit receives identification information not included in said relay processing information, said relay management means newly registers said identification information in said relay processing information so that relay transmission is executed for all ports except said reception port.