A data communication system has: a cabin module with a transmission and reception unit; and a furniture module, which is fastened in a furniture item anchored in a cabin, and has a transmission and reception unit. The transmission and reception units each have a controllable light source and a light sensor. The furniture module is disposed relative to the cabin module such that light emanating from the light source of the transmission and reception unit of the cabin module is detectable by the light sensor of the transmission and reception unit of the furniture module and light emanating from the light source of the transmission and reception unit of the furniture module is detectable by the light sensor of the transmission and reception unit the one cabin module.