  In this paper, we study information transport in multiplex networks comprised
of two coupled subnetworks. The upper subnetwork, called the logical layer,
employs the shortest paths protocol to determine the logical paths for packets
transmission, while the lower subnetwork acts as the physical layer, in which
packets are delivered by the biased random walk mechanism characterized with a
parameter $\alpha$. Through simulation, we obtain the optimal $\alpha$
corresponding to the maximum network lifetime and the maximum number of the
arrival packets. Assortative coupling is better than the random coupling and
the disassortative coupling, since it achieves much better transmission
performances. Generally, the more homogeneous the lower subnetwork, the better
the transmission performances are, which is opposite for the upper subnetwork.
Finally, we propose an attack centrality for nodes based on the topological
information of both subnetworks, and further investigate the transmission
performances under targeted attacks. Our work helps to understand the spreading
and robustness issues of multiplex networks and provides some clues about the
designing of more efficient and robust routing architectures in communication
systems.
