Recently a supplier of ours announced that we could finally host their shitty java app on Linux instead of paying fucking Oracle for Solaris. So we were eager to hear the requirements. It was RHEL 8.4 or something, a version that was already EOL at the time.
They can't even update their distros apparently.
An OTDR sends pulses of laser light into a fiber optic cable and records the minute reflections that occur at every point of the cable over time. The time of arrival of the reflections corresponds to the position of where it was reflected. This way you can record the attenuation of an entire cable just from shining in pulses from one end. Good for checking if a new cable was properly installed, or for finding the location of issues in existing cables for debugging.