Equalization
Beginner
Undoing the blurring a long wire does to a signal, by boosting the parts that faded the most.
Novice
Circuits that compensate for a channel’s loss. Because high frequencies fade more, an equalizer boosts them (or subtracts the smeared-out echoes of earlier bits) so the receiver can tell the levels apart again.
Expert
Transmit FFE, receive CTLE, and DFE or ADC-plus-DSP FFE/MLSE. More loss to equalize means more taps, faster ADCs and more power; noise is boosted along with the signal, so loss budgets cannot grow indefinitely.