Data flow, functional: datatstream -> encoder -> codestream -> decoder
Data flow, hardware: source -> source encoder -> channel encoder -> modulator -> (channel) -> demodulator -> …
Modulator converts a codestream into channel signals. The output from demodulator is typically not the same as what was inputted because of noise, distortion, interference…
Channel decoder uses redundancy to try restoring the codestream it got from demodulator.
codeword is a data + redundancy.