Communication system and communication method

A communication system comprising:

• a transmission-side processing device, and
• a reception-side processing device,
• the transmission-side processing device and the reception-side processing device communicating using a plurality of communication lines,
• wherein the transmission-side processing device concurrently transmits the same telegraphic messages via each of the plurality of communication lines, and
• the reception-side processing device is capable of concurrently receiving telegraphic messages via each of the plurality of communication lines, and when a same telegraphic message as a previously received telegraphic message is received later, invalidates said same telegraphic message received later while processing the previously received telegraphic message,
• the transmission-side processing device includes a priority determiner which determines a priority of a telegraphic message to be transmitted and transmits the telegraphic message via the plurality of communication lines or one of the plurality of communication lines according to the priority determined by the priority determiner,
• the reception-side processing device is provided in a transport vehicle which transports an article,
• the transmission-side processing device is provided in a controller which controls the transport vehicle, and
• the priority determiner determines that the priority is high if the telegraphic message contains an instruction which causes the transport vehicle to execute a predetermined transport or travel operation, and determines that the priority is low if the telegraphic message does not contain the instruction.