Patent ID: 8126611

Claim:
A communication system to be mounted on a car, wherein a plurality of buses is connected to each other via a relay connection unit, and at least one electronic control unit is connected to each of said buses, said relay connection unit has a storage section having a ROM storing a basic routing table indicating a correlation between a message ID (identifier) to be relayed and a bus through which said message is to be sent and a RAM storing a rewritten additional routing table indicating a newly added correlation therebetween; a message creation section creating a transmission list report message indicating a correlation between said message ID (identifier) to be relayed and said bus through which said message is to be sent based on said basic routing table of said storage section and said additional routing table thereof; and a table creation section creating said additional routing table to be stored in said RAM, said relay connection unit sending said transmission list report message to all of said buses connected thereto; said electronic control unit which has received said transmission list report message via said bus sends a transmission request message of a message ID, of necessary messages ID, which said electronic control unit has not received to said relay connection unit; at said table creation section of said relay connection unit, said relay connection unit which has received said transmission request message creates a new routing table, of an added message, indicating a correlation between said message ID requested by said transmission request message and said bus, through which said message is to be sent, connected to said electronic control unit which has sent said transmission request message and stores said new routing table by rewriting said RAM.