Virtual Serial Ports over Ethernet

Industrial automation systems and production lines gain significant benefits by routing their RS232 data over network. These solutions are also useful when dealing with serially-based point-of-sale equipment that needs to be accessed from a remote location. The point of using a virtual serial connection is that users interact with the hardware as if it was locally attached to the computer.

Virtual COM Port Usage Scenario

You need to access a peripheral device at a considerable distance from your computer. The application that will process the information from the device is installed on your machine, but it has no physical serial interface. Serial to Ethernet Connector can be used in this case to establish communication. It will create a virtual port that can be accessed by the program.

Serial to Ethernet Connector on Linux provides the same functionality as the Windows version of the application and is easy to install. But there are also alternative methods to send serial data over the network using tools that are included as part of most Linux distributions.

The first option is to use netcat to pipe serial data. This can become difficult to manage, since you need to open a separate instance of netcat for each serial connection. You can create a xinetd service (a text file called testservice in the xinetd.d directory) to create persistent connections like this:

service testservice
{
port = 5900
socket_type = stream
protocol = tcp
wait = yes
user = root
server = /usr/bin/netcat
server_args = "-l 5900 < /dev/ttyS0"
}

It will also be necessary to change /dev/ttyS0 to the name of the connected serial device.

Some other tools that have been tested and can provide virtual serial port over Ethernet on Linux machines are:

• ser2net - Serial to Network Proxy (ser2net)

This utility allows users to connect to a serial port from the network. It’s a tool for serial port setup and configuration. It is also useful for modifying port parameters as well as controlling and monitoring serial interfaces.

• remtty - remote tty

Short for "remote tty”, remtty uses pseudo ttys to establish network connections. Using this tool enables Linux users to replicate the functionality of Cisco's Windows-based Dialout application and use direct connections to machines with dial-out modems to fax and send messages.

When using a serial port emulator, data generated from a serial application or device is converted to information that can be transferred over an IP-based network. Once the COM signals are in TCP/IP format they can be transmitted over any IP-compatible network such as your company’s LAN or the Internet, and a virtual serial port provides all of the functionality of a physical COM interface. Data is converted in both directions to allow network transmission and then turned back to serial signals for interaction with devices and programs.

Serial over Ethernet software allows users to connect remote, network-connected serial ports and devices. It accomplishes this by creating virtual serial ports that emulate physical interfaces. With a serial port emulation utility, you can use computers without COM ports to connect to remote serial devices without any additional hardware or cabling.