When modem control is enabled for a port, the PortMaster interprets the data carrier detect (DCD) signal as follows according to the type of ports:
| Login | If carrier is not asserted, the port is unavailable. If carrier is asserted, the PortMaster initiates authentication and displays a login prompt. |
| Device | If carrier is not asserted, the port is unavailable. If carrier is asserted, the port is available for the device service. |
| Twoway | If carrier is not asserted, the port is available for device services. If carrier is asserted, the port attempts to establish a network connection and disable the device service. |
| Network Hardwired | If carrier is not asserted, the port is unavailable. If carrier is asserted, the port attempts to establish a network connection. |
| Network Dialin | If carrier is not asserted, the port is unavailable. If carrier is asserted, the PortMaster initiates authentication and displays a login prompt. |
| Network Dialout | The assertion of carrier has no effect, but the transition of carrier from asserted to not asserted causes the port to be reset. |
| Network Twoway | If carrier is not asserted, the port is available for network dial-in. If carrier is asserted, the port attempts to establish a network connection and disable the network dial-in. |