  Complex systems are successfully reduced to interacting elements via the
network concept. Transport plays a key role in the survival of networks. For
example the specialized signaling cascades of cellular networks filter noise
and efficiently adapt the network structure to new stimuli. However, our
general understanding of transport mechanisms and signaling pathways in complex
systems is yet limited. Here we summarize the key network structures involved
in transport, list the solutions available to overloaded systems for relaxing
their load and outline a possible method for the computational determination of
signaling pathways. We highlight that in addition to hubs, bridges and the
network skeleton, the overlapping modular structure is also essential in
network transport. Moreover, by locating network elements in the space of
overlapping network modules and evaluating their distance in this "module
space", it may be possible to approximate signaling pathways computationally,
which, in turn could serve the identification of signaling pathways of complex
systems. Our model may be applicable in a wide range of fields including
traffic control or drug design.
