The ADTRAN DSU III AR is a technologically advanced, high performance data service unit/channel service unit. This unit provides a reliable interface between the digital data service (DDS) or 4-wire Switched 56 (SW56) network and the customer's data terminal equipment (DTE). The unit is an all-rate DSU/CSU supporting synchronous and asynchronous data rates on the primary channel and asynchronous data rates on the secondary channel. Additional features of the DSU III AR include a DTE-to-service rate matching feature for both dedicated and switched modes, as well as various anti-streaming time-out values, to disable streaming terminals on a multi-point circuit. Private networks and modem tail circuits are accommodated through clocking/timing options.