P$4\mathrm{.}13.$ Consider the block diagram of a typical digital transmission system. Speculate where one would use source coding or channel coding. Differentiate between them. Would they increase or decrease the original message size? $($Hint: We want to transmit most efficiently that is$,$ message size should be the smallest possible, but enough redundancy should be added to correct small errors so that retransmission is avoided as far as possible.$)$