Before revision:  For the general form (no congestion, general weights, integral routing) {\sc   even the case of unit capacity trees which are stars generalizes the maximum matching problem for which Edmonds provided an exact algorithm.
After revision:  For the general form (no congestion, general weights, integral routing) {\sc edp even the case of unit capacity trees which are stars generalizes the maximum matching problem for which Edmonds provided an exact algorithm.