Vehicle-mounted communication system and communication method

An in-vehicle communication system is provided with: an optical coupler; a first in-vehicle device group composed of a plurality of in-vehicle devices connected to a first end of the optical coupler; and a second in-vehicle device group comprising a plurality of in-vehicle devices connected to a second end of the optical coupler, each of the in-vehicle devices of the first in-vehicle device group being capable of communicating with each of the in-vehicle devices of the second in-vehicle device group via a common transmission path in the optical coupler, each of the vehicle-mounted devices of the second vehicle-mounted device group can communicate with each of the vehicle-mounted devices of the first vehicle-mounted device group via a common transmission path in the optical coupler. 车载通信系统具备：光耦合器；第一车载装置组，由连接至所述光耦合器的第一端的多个车载装置构成；以及第二车载装置组，由连接至所述光耦合器的第二端的多个车载装置构成，所述第一车载装置组的各所述车载装置能够藉由所述光耦合器中的公共的传输路径与所述第二车载装置组的各所述车载装置进行通信，所述第二车载装置组的各所述车载装置能够藉由所述光耦合器中的公共的传输路径与所述第一车载装置组的各所述车载装置进行通信。