Abstract: A communication system which enables conventional telephone-type facsimile apparatus to reliably and efficiently communicate over a conventional two-way voice radio communication system. The system includes an interface unit which is connected to the facsimile aparatus and to the transceiver apparatus of the radio communication system without modification to either unit. The interface unit transmits and receives information over the radio system in the form of a series of data packets, each containing check digit information to verify transmission accuracy. To optimize data transmission in the presence of weak signals or noise on the radio channel, the packet speed for a link between two stations is selected adoptively as the highest available data speed which yields a predetermined minimum packet error rate.