Provided herein is a transgenic bacteria engineered to accumulate carbohydrates, for example disaccharides. The method displays a present advertisement, determines whether the present advertisement has been displayed completely, and adds an identifier of the present advertisement to a priority advertisement list if the present advertisement has not been displayed completely. The communication system also includes a communication node comprising an optical modulator optically coupled to a second end of the optical link, wherein the optical modulator is operable to receive a signal, to modulate the light from the laser with the signal, and to propagate the modulated light to the communication hub.