Algorithms to Realize Directed Communication Nets

Necessary and sufficient conditions are formulated for a real square unsymmetric matrix R to be the terminal capacity matrix of a directed communication net. These conditions lead to a practical set of realizability tests and are used to derive easily tested sufficient conditions for realizability. The sufficient conditions include several previously known realizability conditions as special cases and answer some hitherto unsolved problems concerning the range of applicability of a number of realization schemes.