User guide

Common User Scenarios
Chapter 8 Modem Emulation 36
Common User Scenarios
The Digi device server in modem emulation mode allows for the easy replacement of modems in almost any
environment where there is a LAN or WAN.
In Diagram A, the Digi One TS replaces a modem connected to a workstation running an application. The Digi
One TS allows for the use of software applications without modification by responding to all the AT commands
configured in the workstation application. The Digi One TS connects to the IP Address of the server when an
ATDT ipaddress:port (ATDT 192.168.25.5:50001) command is issued. Once the remote device
establishes the TCP connection, a CONNECT message is sent to the serial port and only then does the Digi
device server 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 will be sent to the application if the
remote side closes the TCP connection.
In Diagram B, two Digi device servers will replace modems on both sides of the connection. The initiation of the
connection occurs with either of the Digi device servers. If both ends are Digi device servers, 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 server 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.
Modem emulation has the ability to communicate to an infinite number of other devices.
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Server
Workstation
Digi One TS
#1
Ethernet
Serial cable
192.168.25.5
User Scenario-Diagram A
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192.168.25.30
Workstation
Digi One TS
#1
Digi One TS
#2
Ethernet
Serial cable
User Scenario-Diagram B
Serial cable
Workstation