A communications management system service as an interface between an ADSL (Asynchronous Digital Subscriber Line) terminal and an ATM exchanger. The system includes a control section, an upstream cell processing section, and a down stream cell processing section. The control section receives user cell signals from a subscriber terminal and converts the user cell signals to ATM cells. The upstream cell processing section then converts the ATM cells into signals for transmission to a subscriber control system. The downstream cell processing section converts signals received from the subscriber control system to ADSL signals to be sent to the subscriber terminal. The ADSL signals may be E1 signals. To check for errors in the system, the controller sends a test cell through the system. When the test cell loops back to the controller, it is compared to the test cell as it was initially generated. A decision concerning system errors is then made based on this comparison.