Advanced Operating Modes of Serial to Ethernet Device Server

Ethernet Modem

The Ethernet Modem Mode is designed for applications which use PSTN for the communication. TCP/IP Ethernet wasn’t ready at that time and applications used analog modem for dial in/out in the past. The connection speed was slow and the cost was high. With the Ethernet Modem Mode, the analog modem can be replaced by the device servers, one on each end. After the IP addresses are assigned, the user can dial the IP address with TCP port number (IP:TCP Port) instead of the phone number with the same modem AT commands. All users can enjoy the high speed of the Internet connection, and with almost no additional cost.

Terminal Mode

In applications with Terminal to the Servers (such as Windows or Unix), the serial link was the only way for it. However, the Terminal Mode offered by the device server provides an alternative method for the Terminal to connect to the servers over the Ethernet network. The terminals connect to the devices via a serial cable and the device server connects to the servers via the Ethernet connection. There are two types of Terminal Modes, the ASCII and Binary.

Terminal ASCII Mode: This is used for the text-based terminal application. The data should contain no binary (file transfer) or encryption. The Terminal ASCII mode can handle up to 8 sessions per port. It also allows users to switch between sessions on the same terminal.

Terminal BIN Mode: The Terminal BIN (Binary) mode allows users to transfer the file or encryption between the terminals and servers. In this mode, only one session can be perform at one time.

SSH: Some of the data or commands that transfer between the terminals and servers are sensitive, additional security should take place for these data. With the SSH mode, the data will be encrypted with SSH (Secure Shell) protocol over the Ethernet network. It allows only one session per port at one time.

Reverse Terminal Mode

This operating mode, Reverse Terminal, is similar as the Terminal Mode above. Both are used for the connection between a terminal and a server. The major difference is the direction of the connection initialization. The terminal is connected through the network and the server is connected through the serial port. The reverse terminal session typically involves a network administrator telnetting to a device that has a dedicate serial console port used specifically for the configuration purpose. This mode is common in configuring the devices such as routers, UPS (uninterrupted power supply), and other devices with console/AUX or com ports to which a terminal can be physically connected for console management. Administrators may use the serial console for security reasons for the legacy devices or as a backup configuration method when the network is down.

Reverse Telnet: Reverse Telnet is commonly used for device management in telecommunication control rooms. Since the control commands such as CR/LF can not be transmitted by the TCP Server mode, the Reverse Telnet is the best solution for this type of application.

Reverse SSH: The Reverse SSH model allows the user to use SSH utilities such as PuTTY for the remote connection.

Printer Mode

Lots of industrial printers come with the serial connectivities. The Printer Mode is an excellent solution for the huge printing demands. The printer mode allows the host PCs to send the printer data to the serial printers in either RAW or LPD modes.

Raw PRN: RAW Printing. The RAW printing is designed for printers such as receipt printers and barcode printers. Many terminal printers are able to accept the raw data as well.

LDP_PRN: The LDP is a printer protocol which uses the Ethernet to connect between the printers and workstation/servers. To use this operating mode, the printers should have built-in LPD software, and the LPR software must be installed in the workstations/servers. The LPR will send the print queues to the print server (device server in this case), and prints it when the printer is available.

The Dial In/Dial Out Mode

For the ISPs and enterprises that need a remote access solution. Users can use PPP dial-up connection to access the device server via PSTN over the analog modems. The device server works as a server and grant the user a legal access to the network regardless the operating system the user uses. The Dial In/Dial Out mode supports PPP, SLIP and Terminal modes for the access.


The Disable is not actually a operating mode. It disables the unused serial port for security purposes. When a serial port is set to disable, this port is not functional.

Here are the device servers with the above mentioned functions.

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