When a signal propagates down a wire and reaches a change of impedance it will cause a reflection, it is one source of noise.

Ringing is when a signal changes level, then overshoots then settles back down , undershooting a little then finally coming back up to get to the final level it's supposed to be at.



Say you can or say you can't, either way you will be right.
Computers are like old testament gods: Lots of rules and no mercy.