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Extra Characters When Connecting to the Serial Port on a Digi TransPort Using Telnet

This issue may arise when using Telnet when opening socket connections to a Digi TransPorts serial port.  This can occur when using the built-in Microsoft Windows Telnet client, or third-party terminal emulation software such as PuTTY.

This type of connection is most common when a TransPort is being used for out-of-band access.  An example of this would be accessing a Cisco's console port via the TransPort.  By default, the TransPort uses a base socket of 4000 for its serial ports.  By default, it is possible to reach the TransPorts serial port by using 'telnet Ip_address_of_transport 4000' from a Windows command prompt.

In some instances when connecting to the serial port, it is possible to get a double character echo on the terminal windows, which can prevent the terminal window from interacting with the end device properly.

Microsoft Telnet Issue

If Microsoft Telnet is used, the following settings need to be adjusted on the Digi TransPort:

1)  In the WebUI, navigate to Configuration - Network > Advanced Network Settings.

2)  On this page, locate the section titled Serial Port Telnet Modes, then Serial Port 0 Telnet mode, and change this parameter to Telnet no null stuffing, as shown below:

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3)  Make sure to Apply and Save the changes after they have been completed for this to take effect.

4)  Once this is complete, the double characters should no longer be occurring.


PuTTY Issue

If PuTTY is being used as the Telnet client, local echo will need to be disabled within PuTTY to prevent echo character issues.

1)  To disable the local echo option within PuTTY, launch the PuTTY program and click Terminal on the left hand side.

2)  Under the Terminal section, check Force off for the Local echo field, as shown below:

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3)  Now when the connection to the serial port is made, the characters should no longer echo as they previously would have.
Last updated: Aug 23, 2017

Filed Under

Cellular/Transport

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