User`s guide

Chapter 8 Special Features: Modem Emulation 67
Modem Emulation
Modem emulation enables a system administrator to configure a
networked Digi device to act as a modem. The Digi device emulates
modem responses to a serial device and seamlessly sends and receives
data over an Ethernet network instead of a PSTN (Public Switched
Telephone Network). The advantage for a user is the ability to retain legacy
software applications without modification and use a less expensive
Ethernet network in place of public telephone lines.
Note: Port one on the PortServer TS 1/3 M MEI is an actual embedded modem. The
remaining ports are capable of emulating a modem.
To use a Digi device for modem emulation, do the following:
• Use a cable with the correct wiring pinouts (see "Modem Emulation
Cable Signals" on page 68)
• Configure the serial ports and device type with the Web Interface
serial port profile - Modem Emulation
Note: Before AT commands are accepted, DSR must go high on the Digi device.
Common User Scenarios
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.
In Diagram A, the PortServer TS 1 MEI replaces a modem connected to a
workstation running an application. The PortServer TS 1 MEI allows for the
use of software applications without modification by responding to all the
AT commands configured in the workstation application. The PortServer
TS 1 MEI 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 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
Chapter 8
Special Features: Modem Emulation