Install isdnutils-xtools by entering the following commands in the terminal:
sudo apt update sudo apt install isdnutils-xtools
Description:
ISDN utilities - graphical tools
This package provides xmonisdn and xisdnload, which are graphical tools for ISDN. Each in its own way gives a visual indication of the status of the ISDN lines, so that (for example) it is obvious when there is a connection. . They have been split out into a separate package to allow the others in the suite to avoid dependencies on the X Window System.
Homepage: https://www.isdn4linux.de
Version: 1:3.25+dfsg1-9ubuntu2
Section: universe/x11