In information theory, there are two concepts that are widely used: source encoding and channel encoding.
I'm afraid I may not be capable of expressing my doubts clearly, but the thing is that I don't understand they interact between each other.
To try to make it clearer, I'll try to give an example of my doubts:
Every codeword for the channel encoding must have the same length. Why is this? If the source from which the channel is reciving its input used a Huffman code, for example, lengths might be different for each symbol. Isn't that a contradiction?