Common User Scenarios for Modem Emulation

The Digi device in modem emulation mode allows for the easy replacement of modems in almost any environment where there is a LAN or WAN.

User Scenario - Diagram A

In Diagram A, the Digi device replaces a modem connected to a workstation running an application. The Digi device allows you to use software applications without modification by responding to all the AT commands configured in the workstation application. The Digi device connects to the IP Address of the server when you issue the following command:

ATDT ipaddress:port (ATDT 192.168.25.5:50001) 

Once the remote device establishes the TCP connection, a CONNECT message is sent to the serial port and only then does the Digi device switch from AT command mode to data mode. Using the modem escape sequence or dropping DTR on either side terminates the connection. A DISCONNECT message is sent to the application if the remote side closes the TCP connection.

 

User Scenario - Diagram B

In Diagram B, two Digi devices replaces modems on both sides of the connection. The initiation of the connection occurs with either of the Digi devices. If both ends are Digi devices, the TCP listening port number is 50001 for port 1. An example of the connection command is:

ATDT 192.168.25.30:50001. 

Upon establishing a successful TCP connection, a CONNECT message is sent to the serial port, and only then does the Digi device switch from AT command mode to data mode. After the CONNECT is received, the transmission of data begins. Using the modem escape sequence or dropping DTR on either side terminates the connection.