  Information Theory concepts and methodologies conform the background of how
communication systems are studied and understood. They are mainly focused on
the source-channel-receiver problem and on the asymptotic limits of accuracy
and communication rates, which are the classical problems studied by Shannon.
However, the impact of Information Theory on networks (acting as the channel)
is just starting. Here, we present an approach to understand how information
flows in any connected complex network. Our approach is based on defining
linear conservative flows that travel through the network from source to
receiver. This framework allows us to have an analytical description of the
problem and also linking the topological invariants of the network, such as the
node degree, with the information flow. In particular, our approach is able to
deal with information transmission in modular networks (networks containing
community structures) or multiplex networks (networks with multiple layers),
which are nowadays of paramount importance.
