Modem is designed to provide the user with trouble-free data transmission in both self-healing ring and multi-drop string configurations. It has self-diagnostic capabilities that can be monitored on a computer via the front-panel mounted RS-232 or USB ports. A front panel mounted RS-485 port is provided for interconnecting the network diagnostics on two or more master modems. The PC based network management system incorporates real time system diagnostics for monitoring various network and modem parameters.