DSP (in an optical module)
Beginner
The chip inside an optical module that cleans up the signal on both sides, like a translator who also fixes typos.
Novice
A digital signal processor that retimes and equalizes the signal twice: once for the electrical link from the switch chip, and once for the optical link. It makes each half of the link independent, but it is the hungriest part of the module.
Expert
A full retimer per lane on the host side plus PAM4 transmit/receive DSP (ADC, FFE, sometimes MLSE) on the line side, with gearboxing and FEC monitoring. Often around half of module power. Removing it is the point of LPO.
Explained in Optics (Systems).
See also: Retimer, Linear-drive pluggable optics (LPO).