When there are unused communication channels, it is checked whether an attribute of an image associated with transmission image data indicates color image data or monochrome image data. If the transmission image data is monochrome image data, the image data is transmitted through one of B channels...http://www.google.de/patents/US5774654?utm_source=gb-gplus-sharePatent US5774654 - Communication terminal apparatus and communication method for communicating data through a plurality of communication channels 
