  Explicit characterization and computation of the multi-source network coding
capacity region (or even bounds) is long standing open problem. In fact,
finding the capacity region requires determination of the set of all entropic
vectors $\Gamma^{*}$, which is known to be an extremely hard problem. On the
other hand, calculating the explicitly known linear programming bound is very
hard in practice due to an exponential growth in complexity as a function of
network size. We give a new, easily computable outer bound, based on
characterization of all functional dependencies in networks. We also show that
the proposed bound is tighter than some known bounds.
