The ADTRAN DSU III AR provides a reliable, high speed data connection for customer Data Terminal Equipment (DTE) through Digital Data Service (DDS) lines, DDS secondary channel services (DDSII), or 4-wire Switched 56 network (SW56) lines. The DSU III AR supports both synchronous and asynchronous data communication over the DDS or 4-wire Switched 56 networks. This manual outlines and the installation and operation of the device.