How to Redirect Serial to Telnet? Serial toTelnet Windows and Linux guide

Telnet usage fields

The format of a Telnet command is as follows (use your actual computer name when connecting):

telnet your.remote.computer.name

After entering this command you would be presented with a login screen and need to provide a userid and password. If your credentials are correct, you are then logged in as if you were a local user.

Telnet is primarily used to satisfy the need to access designated applications or data that are located on a particular computer that is located remotely. Serial devices that are attached to a remote server can be accessed by using the Telnet RFC 2217 protocol. Examples of these devices are:

• industrial monitoring devices such as water flow control monitors
• medical monitoring equipment
• serial printers and scanners
• copiers, cash registers, and other serially attached equipment

General connection settings:

1. Open local real port only when connection is established – this option is available when you create a connection on a real telnet RS232 port. You can maintain this port’s availability for use by local applications when it is not connected to a remote machine.
2. Connect to remote end only when local virtual port is open – this setting is used when the connection uses a virtual telnet serial port. When enabled, the local COM port must be opened by an application before any connection attempts are made.
3. On error retry to establish connection every – when this option is chosen, retries of failed Telnet to COM connection attempts will be made based on a specified time interval.

Network protocol settings:

• Raw data transmission protocol: Use of this transmission mode enable the establishment of a raw TCP session. All data is subsequently sent with no protocol-specific or application layer formatting.
  
  
• Use Telnet protocol (RFC 2217):Telnet with RFC 2217 extensions allows server and client to exchange the telnet ip port configuration information. The remote end can be notified of changes made to the settings or the state of the local serial port.
  
  
• RFC 2217 mode was originally designed to be used with modems, but can also be used for serial printers, scanners, laboratory monitoring devices, and office equipment.

Serial to Ethernet Connector allows you to forward serial port over network easily when using RFC2217. Use the instructions above and you can soon be working with serial devices over the network.

Serial to Telnet Issue

Let’s take a look at an application that utilizes a serially connected device, and employs a COM port, like a GPS reader.

We would like to be able to use a device connected to a computer (server) to be accessed by an application that is running on a network-connected remote computer (client). An example would be having a device connected to the small, single-board PC ODROID. After connecting the ODROID to the network, we want to read the device’s data on our local desktop.

If, as we suspect, the application must use a serial port to communicate with the device, then the client computer needs a virtual serial port for the application to use.

Then the application interacts with the client machine’s serial port and is not concerned by the fact that the data is being sent over the network.

The solution in theory

One of the solutions to this problem is to use Telnet with RFC2217 - Telnet Com Port Control Option. There are many software tools that supports Telnet+RFC2217 serial port forwarding, enabling you to run server and client machines on the Linux or Windows platforms. The interoperability of RFC2217 and Telnet means that a Linux server and Windows client can communicate using completely different software packages, as the underlying protocol is the same. You also have the ability to configure parameters, for example to multiplex the serial ports or enact data encryption when using RS232 to telnet. This solution helps to forward serial port over network without any problems.