  The propensity for synchronization is studied in a complex network of
asymmetrically coupled units, where the asymmetry in a given link is determined
by the relative age of the involved nodes. In growing scale-free networks
synchronization is enhanced when couplings from older to younger nodes are
dominant. We describe the requirements for such an effect in a more general
context and compare with the situations in non growing random networks with and
without a degree ordering.
