Abstract: A data set connecting a data terminal to a data channel for concurrently transmitting and receiving data. Full duplex operation is achieved over the data channel which is typically a two-wire telephone line. In one configuration, a data set receives signals from a computer and transmits frequency shift keyed signals through a telephone central office to a display unit attached to a remote telephone handset. Multifrequency signals from the telephone handset are transmitted over the telephone line to the data set where they are detected, decoded and transmitted to the computer.